A dim image may occur due to filament emission from the kinescope. The same reason can cause a gradual attenuation of the glow and its restoration when the TV warms up. This problem can be eliminated, although not for long, by bridging the protective resistor in the power circuit kinescope filament . Another option kinescope restoration in case of such a malfunction, this means winding an additional winding on the core of the winding transformer and using it as a supply winding for the filament. But don't forget, this won't last long. And in the future, you will still have to replace the screen. If the screen glows brightly and reverse lines are visible (these are thin horizontal light lines that are located throughout the entire screen or on some part of it), then such a kinescope cannot be restored. However, I would like to note that such a malfunction can occur for other reasons. Therefore, you should check all components of the TV before deciding to replace the screen.
Checking for a broken filament is very simple: first, you need to pay attention to whether the filament in the neck of the kinescope is lit when the device is turned on. If not, then you need to turn off the TV, remove the picture tube panel and check whether there is a circuit between pins 9 and 10 (the filament, designated Heater). If the circuit is missing, then a break has occurred and the screen cannot be restored.
With the kinescope panel removed, it is necessary to apply the supply voltage to the filament (6.5 - 7.5V), i.e. to pins 9 and 10 and wait a bit until the kinescope warms up. After this, you need to take a device (ohmmeter, multimeter), set its scale to measure a resistance of at least 20 kOhm, connect the negative terminal from it to the modulator (G1), and connect the positive terminal one by one to the cathodes (KG, KR, KB) and see if there is resistance between the modulator and these cathodes. With a working kinescope, the resistance should be close to infinite, i.e. the device should not show anything. If there is some resistance that is visible on the device, then a short circuit has occurred between the modulator and the cathode on which this resistance is visible. This reason also contributes to the disappearance of all colors, just one or two.
In the same way, the closure of the accelerating voltage contact (G2) with the other contacts and the focusing contact (G3) is also checked with other contacts. Only in these cases should the negative terminal of the device be connected to the accelerating or focusing terminal, depending on which contact you are checking. The resistance parameters during these tests should be the same as when testing a modulator with color cathodes, i.e. the resistance should be close to infinity.
Take an independent power source with an alternating voltage of 6...8V and, with the TV turned off, supply this power to the kinescope filament (use a separate kinescope board).After supplying power to the kinescope filament and warming up, you need to take a capacitor with a capacity of 100...220 uF and a voltage of 350...450 V, solder the leads from the wiring to it and charge it from the outlet (while observing safety precautions when working with high voltage). Then connect one terminal of the capacitor to one of those contacts between which a short circuit has occurred, and touch the second terminal of the capacitor to the other closing contact, so that at this moment the capacitor is discharged. You will hear a characteristic click - this means that a discharge has occurred and the phosphor particle that caused the short circuit has burned out. This method is also called “kinescope shooting”.
20/08/2009 - 21:25
Picture tubes and their problems.
I suggest writing in this thread about the problems of kin and how to restore them.
The first method of eliminating a short circuit. Applicable ONLY to tube TVs, color and b/w, which have scanned lamps, of which we still have a lot in our region. So, if a short circuit is diagnosed, no matter between which electrodes, we do this.
We disconnect the kinescope board from the BC (or unsolder the cathode from the UPCH board), remove the suction cup from the anode, take it with something well insulated (God forbid you drop it!) and turn on the TV. After the scanner has warmed up (the suction cup begins to hiss), we bring the suction cup to the kinescope board and begin to have fun. At a distance of 2...3 cm, sparks begin to fly between the PC and the suction cup - no need to be scared! We move the suction cup AROUND the board, ensuring that a spark hits all the electrodes. In this case, there must be a filament on the kinescope and a ground on the board itself. Turn off the TV, connect the PC and make sure that everything is normal. This is not a joke, the method was proposed by a master (I think his name is Alexander Lopatkin, he worked in Peterhof) from St. Petersburg. The method has been tested many times - nothing bad has ever happened to the remaining elements of the circuit, but the short circuit is knocked out in one go. Picture tubes also live happily after such an operation.
Let me remind you about safety precautions - SOMEONE MUST BE NEAR, AND YOU NEED TO HOLD THE SUCKER WITH SOMETHING ELECTRICALLY RELIABLE (I clamp it between two long boards).
The second way to eliminate the short circuit. If the kinescope is hooked (especially on Soviet TV), and the owners don’t have money for a new one, don’t push it. In many cases, it is enough to add voltage from the MP. ZUSTST and the like normally hold 145...150 V, the kinescope after that lasts another 1.5...2 years.
The third way to eliminate the short circuit. Many methods have been proposed in the literature for protecting picture tubes based on delaying the supply of high voltage. If the TV has one power source, which, when switching to standby mode, does not change the output voltage too much, I recommend that you simply turn on the kinescope heat from the power supply through a six-volt KREN, screwing it to a suitable piece of hardware in the TV for heat removal. At the KREN output, a KS168 zener diode is required to protect the kinescope in the event of a breakdown of the microcircuit. The switching procedure becomes a little more complicated - first we turn on the TV in standby mode, wait 1...2 minutes, then turn on the TV. Switching off is in reverse order. The beauty of this method is that the image appears immediately, without cloudy heating. There is one BUT - it is not recommended to run the heater on for days - the kinescope is sideways, but the magnets on the neck may begin to lose their properties after 1...2 years.
Important addition.
There was a case of a red filament cathode shorting in a SHARP 21" with the same classic manifestation. However, when installing its filament winding, the TV began to go into protection immediately. It behaved the same way with the kinescope filament leads disconnected. When considering the filament circuit It turned out: one terminal is grounded, the second goes to the TDKS winding. From there, an inconspicuous semiconductor leaves and goes into the depths of the circuit (voltage control?). We got two options:
1) its own filament winding and a 10 Ohm 5 W resistor to the TDKS winding as a load for deception. Tried (short term) - works:
2) isolation transformer. It was wound on what was at hand - the fuel assembly core of a portable TV. Wound with wire in PVC insulation, exchange. I -10...20 turns, II - resp. 11...21 turns. It is not critical to select the turns of winding II based on the equality of voltages on the windings when a kinescope is connected and measured with a voltmeter in both directions. Windings should only be wound on top of each other! The assembled core is fixed on the kinescope board.
Comment.
With an isolated filament circuit, even during long-term operation, breakdown of the kinescope does not occur - measured with a voltmeter and ohmmeter. So there is no deterioration in clarity.
The fourth way to eliminate the short circuit. On the SHARP TV, the kinescope (green incandescent) has shorted out. The standard thing appears - a few seconds after turning on, the screen turns greener and brighter, reverse lines appear, then the power supply turns off abnormally. This malfunction may be caused by a voltage leak in the video amplifier transistor - this can be checked by replacement. The problem is resolved by changing the filament circuit. On board
kinescope, cut the routes leading to the filament, wind 1...3 turns of mounting wire in fluoroplastic onto the TDKS core. The number of turns must be selected, starting from the 1st, usually two turns, monitoring the heat by eye. It is impossible to miss - after all, the TDKS itself has an integer number of turns. In the circuit in series with the resulting winding, connect a resistor of the same value that was used to limit the filament current (usually 0.5...3 Ohms) and solder the entire structure to the filament terminals of the kinescope. The method is applicable to any picture tubes and has been tested many times, incl. on Soviet TVs. The number of turns in this case needs to be selected. There were no repetitions, the operation is done at home in half an hour. The idea was taken from “Radio”, but there it was proposed to include a pulse transformer in the filament gap (also tested, also effective).
Picture tubes - anti-aging
It is known that the kinescope, like any other part on the TV, is subject to aging. And since this is the most expensive part, it makes sense to try to extend its life. Aging does not occur due to a decrease in the thickness of the cathodes, as some believe, but because, due to the low chemical purity of the metal used to make the cathode, the metal itself is knocked out with the flow of electrons, moving to the anode and mask of the kinescope. The slag remains on the cathode. On imported picture tubes, it is almost impossible to remove them using standard spark methods. I have used a development that allows this to be done using a cathode-modulator plasma discharge. To do this, it is necessary to apply negative pulses to the cathode of the tube relative to the modulator (frequency 2 kHz, amplitude 300 V, burst duration no more than 3 seconds, pulse shape - meander).
It should be remembered that the modulator-cathode current can be approximately 2 A and, accordingly, choose the circuit design. The voltage at the kinescope filament during restoration is initially about 8 V (about 5 pulse trains),
The process can be observed through the neck of the kinescope (a red-yellow glow is formed in the cathode-modulator zone of the restored gun). I have tested this method in practice and found it effective in 100% of cases.
SONY KV-G21T1. Malfunction: the screen lights up brightly in blue with reverse lines, and the beam current limiting protection is triggered. The power supply goes into standby mode. The voltage on the blue video amplifier in standby mode is 114 V; at the moment the kinescope is opened, the voltage drops to zero and the protection is activated. After heating, the filament, which has one contact on the ground, sags and shorts to the cathode of the kinescope. It is necessary to cut the track on the kinescope panel, which is connected to ground, and lay it with a separate wire to the 6th leg of the horizontal scan transformer. Leg 6 of the transformer, in turn, also needs to be cut off from the body.
SONY KV-G21M1. DEFECT. After warming up for one minute, the screen becomes hoarse with white slanted lines. After this, the TV turns off.
FAULT. This defect is most likely associated with the closure of the blue cathode to the filament and, consequently, to the housing. I turn on the TV and check the voltage at the blue cathode. At the moment the blue screen appeared, the voltage dropped to almost zero. The diagnosis was confirmed. Now the repair comes down to the following. I turn off the kinescope filament terminals on the video amplifier board. I wind about two turns of wire with good insulation around the core of the line transformer and solder them to the free filament terminals of the kinescope. I use an ohmic resistance to select the exact filament voltage.
SONY 21 Ml, FUNAI TV2000A-MKII. Within a month, two SONY and one FUNAI TVs came in for repair with the same fault. After 1-2 minutes of operation in the kinescope, the filament shorted to the modulator. One TV is set to blue, and the other two are set to green. The screen glows brightly, one color, and the reverse lines are visible. The protection on the SONY TV was triggered and it turned off. It was possible to restore normal operation by winding an additional incandescent winding directly onto the TDKS core (the winding contains 3.75 turns of MGTF wire, it is secured with glue or mastic). The filament power should be supplied through a limiting resistor with a resistance of approximately 0.5 ohms. All three TVs work fine, the image quality has not deteriorated.
SAMSUNG CS-21AWQ. The TV is 3 years old. First repair after purchase in the second month. The D5073 was damaged from overheating (without a radiator - as they wrote at that time, it was made using new technology). According to the second repair - the TV turns on, there is a high-pitched sound, there is an image and sound, but the picture is very dim and blurry, there is very strong tugging - it feels like a pipe has collapsed, when adding SCREEN the effect is almost zero, when adding FOCUS the brightness is adjusted within small limits, but all the same, all signs of a dead pipe. When checking the kinescope, it was discovered that the blue spotlight was leaking relative to ground. If on a SONY TV, when the modulator is closed, one of the colors is flooded, reversed, and in protection, then here it is a little different. There is only one output, an additional filament winding of about 4 turns, not connected to ground. The quality is quite normal. (If the brightness does not change when the accelerating voltage is reduced, the kinescope is faulty, an interelectrode short circuit has occurred. Moreover, if the defect occurs immediately when the TV is turned on, then particles of the cathode material probably got between the electrodes. Such a short circuit can be tried to be eliminated using a spark discharge. For this purpose, use a charged capacitor with a capacity of 100...200 μF for an operating voltage of 450 V. If the defect does not appear immediately, but after the kinescope warms up, then the filament on the cathode is likely to sag. very little and the kinescope needs to be replaced).
INSTALLING A CINESCOPE WITH A NECK DIAMETER
29mm.
1) Instead of a kinescope with a neck diameter of 22mm.
2) INSTEAD OF A CINESCOPE MADE IN CHINESE (29 mm)
Picture tubes with a neck diameter of 22mm are produced mainly by factories in Japan, South Korea, Malaysia and South America, therefore, due to the distance of these manufacturers from Russia, such picture tubes are more scarce and cost $5-20 more. We can offer installation of a picture tube with a neck diameter of 29mm instead of a picture tube with a neck diameter of 22mm if the following recommendations are followed: It is necessary to purchase a socket for a 29mm picture tube and install it instead of the old socket, or on the back side of the picture tube board, according to the table below (pin numbering is shown when positioned kinescope with the neck towards you).
Picture tubes with a 22mm neck have a filament current of 300 mA. If the filament current again
the installed kinescope is larger (usually 630 mA), then it is necessary to adjust the filament voltage on the TV by reducing the resistance of the quenching resistor in the kinescope filament power supply circuit.
a) European standard 29mm.
b) Asian standard 22mm.
c) Russian standard 29mm.
d) Chinese standard 29mm.
Finally, minor adjustments to the horizontal image size may be required by changing the capacitance of the “flyback capacitor” in the collector circuit
c: horizontal scan input transistor.
On Chinese picture tubes, the focusing voltage is usually somewhat lower,
than on all others.
Panasonic TC-215OR (MX-3 chassis)
The image shows a gray “curtain” from below, which moves up and down when adjusting the accelerating voltage. Where the “curtain” is, the image is out of focus.
Replacing the TA5192K video processor (analogue - AN5192K) did not help, the supply voltages of the power supply were normal. The kinescope turned out to be faulty.
Faulty kinescope - solving the problem
Dmitry Smirnov
A failed kinescope threatens the TV owner with significant financial expenses, since, as a rule, it must be replaced. What if you try to fix it? On the pages of our magazine we have already talked about the restoration of picture tubes and in this article we continue the topic we started.
When starting an article about repairing picture tubes, the author believed that this was a thankless task. Many such articles are written. They offer for consideration devices for restoring the emission of picture tube cathodes (for example, in RET No. 4, 2000), give advice on eliminating interelectrode short circuits in picture tubes, etc. The defect of Trinitron picture tubes, which occurs when the filament sag and shorts to the cathode, is well known. The method proposed below for eliminating this defect is certainly not universal, but in the author’s practice it helped in 70% of cases. Perhaps this article will help someone with repairs, especially since it will not require serious expenses from the technician.
The interelectrode short circuit between the cathode and the heater of Trinitron picture tubes manifests itself in the same way as in any picture tube from another company. The screen is “flooded” with one of the primary colors in the cathode of which a short circuit has occurred. The reverse lines are also visible on the screen, and after 1...2 s the TV goes into standby mode, because the protection is triggered. The LED on the front panel flashes 4 times.
Rice. 1. Position of the kinescope when eliminating the defect
The essence of the method for eliminating this malfunction is to deform the filament in the direction opposite to the sagging. Obviously, this becomes possible only by heating the filament to a certain temperature, at which the filament becomes light yellow in color.
To implement this method, the master will need a filament transformer with switchable windings for voltages of 6.3, 9, 12...14 V. The transformer must be designed for a power of at least 20 W. It should allow receiving a load current of up to 1 A in the secondary windings at the specified voltages.
Before starting work, you must place the TV screen down, using foam rubber to prevent scratches on the body, and remove the back cover. In order for the filament to deform when it is heated, it is necessary to place a stand 10...12 cm high under the kinescope on one edge, as shown in Fig. 1.
The board is removed from the kinescope and a voltage of -6.3 V is applied to its filament terminals. The cathode heaters must be under this voltage for 15...20 minutes. Then, for 1...2 minutes, a filament voltage of 9 V is applied. In this case, you need to tap on the neck of the kinescope in the area of the filaments, for example, with a thick rubber handle of a screwdriver. Tapping is necessary in order to get rid of small particles on the heater, which during further operation of the kinescope can become a source of short circuit.
After heating the filaments at a voltage of 9 V, it is necessary to increase this voltage to 12 ... 14 V. It should be applied for 15 ... 20 s, and then return to the filament voltage of 9 V. All these manipulations must be accompanied by tapping on the neck of the kinescope . The number of transitions to 12...14 V and back to 9 V can be limited to 4...5. During this time, the filament heats up to a high temperature (light yellow color).
Then you need to turn off the transformer and allow the heaters to cool completely without changing the position of the TV. At the end of all these procedures, you should “run” the TV within 24 hours. If during the “run” the short circuit does not appear, consider that the client is lucky and his wallet will not seriously lose weight. However, it may happen that the short circuit remains. In this case, it is necessary to obtain permission from the client to modify the diagram (preferably in writing). This is necessary for the following reasons:
The master changes the standard design of the product.
The result of the modification may not satisfy the client, and he will try to find a more “qualified” repairman, etc. In practice, the client agrees, especially if the cost of the kinescope is mentioned, and gives any written permission. The diagrams given below are directly related to SONY TV, but the general idea is suitable for devices of other brands, you just need to determine from which transformer windings the filament circuit of the kinescope is powered.
The main idea of the modification is to isolate the filament circuit from the common wire. In the general case, the filament circuit diagram has the form shown in Fig. 2.
Using a sharp knife or cutter, you need to cut off one terminal of the FBT filament winding on the common board and terminal H1 on the kinescope board from the common wire. Then the insulated terminals must be connected with a conductor, and the cathode itself, through which the short circuit occurred, must be connected through a 220...270 kOhm resistor to the filament as shown in Fig. 3.
This modification allows the TV to “live” for quite a long time. Image quality remains satisfactory. True, if the short circuit of the filament to the cathode occurs periodically, then the white imbalance is noticeable at the moment when there is no short circuit. In addition, the effect of “smearing” of the color whose cathode is closed is noticeable. This is due to the significant capacitance between the heater filament and the cathode.
To eliminate, or, more precisely, reduce the influence of this phenomenon, you can introduce an additional transistor into the cathode amplifier by removing some parts.
The changes made to the circuit are shown in Fig. 4. The results of the refinement are quite satisfactory. If the brightness and focus vary, then this is a short circuit between the focusing and accelerating. And if it’s brightness, then it’s an accelerating modulator.
In short:
Step 1: We connect all the pins on the base of the kinescope together (on some kind of socket).
Step 2: We take an unnecessary semi-working chassis (as long as the line works).
Step 3: We hook the casing into the place of the suction cup, and the suction cup onto the prepared kinescope panel. ATTENTION!!! The kinescope ground should not be present on the chassis.
There are just two wires coming out of the camera to the kinescope and that’s it.
Step 4: Start for 1-2 seconds (sparks fly) and immediately cut out.
Step 5: Remove everything, unload the pipe. You put the original chassis in place.
Step 6: Turn on the TV - if the pipe is dark and shooting (garbage cathode modulator),
then you shoot the RGB cathodes with an ordinary shot.
Pay attention to the heat!
This technology is successfully used at the Lvov CRT Plant.
And if it doesn’t help, then let’s go.
By the way, this defect is inherent in Chinese-made picture tubes with a narrow base from IRICO. And all because the heat is not set correctly. Checking kinesis 1. Disconnect the cathodes from the video amplifiers.
2. Turn on the TV.
3. Take an ordinary tester with the DC measurement mode turned on.
4. One probe to the ground, the other to the cathode (the better the cathode, the brighter the screen glow).
5. We look at the readings.
1.2mA* -1.8 mA* - Excellent.
1 mA* -1.2 mA* - Good.
0.7 mA* -0.9 mA* - Satisfactory. Then I think clearly;) Technology for restoring color purity and convergence of rays in “deformed” picture tubes with a diagonal of 37-54 cm.
So we have a picture tube with the mask deformed after a strong impact during transportation, or after a fall. Fill in a different color in the upper corners up to 10cm. See Figure 1.
Step one.
1. Using a scalpel, carefully cut off the compound from the OS alignment spacer wedges.
2. Loosen the clamping screw of the OS mounting clamp.
3. By slowly turning the OS along the left-right axis, we free it from the fasteners and wedges. It is necessary to release it so that it can easily move along the base of the kinescope (it is advisable to carry out this operation while standing facing the screen or from the side).
Step two.
1. Turn on the TV and send a green or red field signal from the GIS (I personally work on the red field).
2. Demagnetize the kinescope with an external loop.
3. Move the operating system along the base to achieve the most “dense picture” (in this case, this happens when the operating system is closest to the so-called “watering can”), simply put, almost close to the pipe (we are not placing wedges yet). We secure the OS with a clamp.
4. Using ring magnets of MSU color purity, we “turn” the spots to the bottom of the screen. See Figure 2. If this cannot be done, then we work at the location of the deformation.
5. Turn on the “mesh field” and use the MSU convergence magnets to converge the rays, while controlling the “angular geometry” by axial (up-down, left-right) movement of the wide edge of the OS. If the result is satisfactory, we wedge.
Step three.
1. Turn on the red or green field.
2. We take four-pole magnets pre-glued to adhesive tape (I use imported high-quality fabric tape), and glue them in the most “problematic” places on the kinescope bulb, having previously adjusted them until the stains completely disappear. Typically there are one or two magnets per spot. See Figure 3.
3. If necessary, we remove the angular mismatch of the rays with magnetic petals. And the raster correction can be corrected within small limits with magnetic rubber strips by gluing them along the edges of the OS.
4. Demagnetize the kinescope. Rotate the TV 90 -180 degrees. If the stains appear slightly, then in this position of the TV you need to turn the magnets a little until the stains completely disappear. If this does not help, then you need to add more magnets or perform the adjustment again.
5. We turn the TV to its original place, demagnetize it again, and if the purity of the color and the convergence of the rays suits us, then the operation can be considered complete. We fix the wedges, OS, MSU with construction silicone or hot melt adhesive.
In a similar way, the operation is carried out on picture tubes that do not have MSU (Philips, Thomson and the like). Then, in addition to the ring magnet (if there is one), I install the MSU, or I remove (if necessary) the ring magnet and install the MSU.
Notes:
1. Four-pole magnets - magnets manufactured using special technology and are widely used for these purposes.
2. Ordinary magnets - such as from dynamic heads, etc. NO GOOD!
3. Eight-pole strip magnets (on a rubber base) - used for correction and color purity within small limits at the corners and edges of the raster. It is mainly glued to the edges of the OS. But gluing on the flask itself is also practiced (for a slight adjustment of color purity). Available in different shapes and sizes (mostly strips of different lengths, widths and thicknesses).
4. Magnetic petals - used to converge rays at the corners and edges of the raster. If you don’t have original ones, you can make them yourself. A strip of the required size is cut out of a PET bottle, and a magnetic petal is cut out of a beer or coffee can; thin permalloy from old Soviet transformers also gives a good effect. They are attached to each other with adhesive tape or thin electrical tape.
ATTENTION! All operations to restore color purity in picture tubes with mask deformation are designed for experienced professionals, and they DO NOT ALWAYS give a positive result. For masters who have no practice in this matter, I advise you to read about static and dynamic convergence of beams in picture tubes with self-convergence of beams. And first, practice adjusting color purity and convergence of beams on a working kinescope. More complete information about this can be read in the book by S.A. Elyashkevich - “Color TVs 3USTST”, or in the magazine “Radio” No. 3 for 1987. TV LG CT-21Q42KEX (MC-019A)
A51QDJ279X KOREA (LG.PHILIPS DISPLAYS)
There is no accelerating voltage, a strong mod-acceleration leak.
Was opened by supply e.g. focusing in the opposite direction (only the accelerator output was put on the ground, for example, the focus was fed 2-3 times to the mod output for a short time). Most experts believe that only two types of malfunctions occur in picture tubes - a short circuit between the electrodes, or reduced emission, since many recommended methods and instruments for testing picture tubes reduce the variety of possible tests to measuring the emission of the cathodes and determining whether there is an interelectrode short circuit. However, each of these broad categories includes a number of intermediate, defective conditions that must be identified for reliable diagnosis and repair.
Broken filament
A broken (burnt out) filament cannot heat the cathodes. A kinescope with such a malfunction cannot be restored. However, this happens quite rarely, since the filaments are made of quite high quality and reliable.
Closing the filament with the cathode
Short circuit of the filament with the cathode occurs when these two elements come into contact due to deformation of at least one of them (as a rule, the filament as a result of sagging, during operation, due to high temperature conditions), or as a result of falling into the gap between them particles of conductive material. The symptoms of this fault depend on how the filament is powered. If an alternating voltage of 50 Hz is supplied to it from the filament winding of the transformer, then when the filament is short-circuited with the cathode, “toffees” appear in the image, the contrast is weakened, and reverse lines may appear. Often the filament voltage is removed from a separate winding of a line transformer, then a short circuit may go unnoticed if this winding does not have a direct galvanic connection with the common wire. The presence of such a connection in combination with a short circuit of the filament will, of course, disrupt the kinescope mode, the image will disappear, the left side of the screen (about half or a third) will be flooded with white light, and on the right side the raster will be less bright.
Often an N-K short circuit appears only after the TV has been running for some time. In this case, it is detected by the sudden appearance of the defects mentioned above in the image.
It is very easy to detect a short circuit in the kinescope filament, if it is permanent, by connecting the ohmmeter probes to the corresponding terminals of the kinescope. Of course, before this you need to remove the socket from the base. If the transition resistance is low (from units to tens of Ohms), this means that the short circuit is caused by sagging filament, and higher resistance values indicate, as a rule, that a foreign particle has entered the H-K gap. In both cases, you should not try to eliminate the short circuit by burning, as is done with cathode-control grid short circuits, since there is a real danger of damaging the filament and completely ruining the kinescope.
The most effective way to eliminate the consequences of a shorted filament is to apply filament voltage through a low-capacity isolation transformer. This is achieved most simply if the cathode is heated from a line transformer. An isolating transformer, in this case, can be made by winding two identical windings of 22 turns each with PEV-0.75 wire on a 1X8.5X6 KZ ring made of M2000NM ferrite.
Closing the control grid with the cathode
Most control grid shorts occur when a piece of conductive material gets caught between the cathode and the control grid. Short circuits between the control and accelerating grids are possible, but occur much less frequently. The control grid, which is closed with the cathode, practically loses its function, the beam current becomes maximum possible, and as a result the screen is filled with bright white or one of the primary colors. Excessive beam current may cause the protection to trip and the TV to turn off.
Like filament shorts, control grid shorts can be permanent or appear some time after the TV is turned on. In the first case, they are detected using an ohmmeter, and in the second, by a sudden increase in the brightness of the screen and often the subsequent turning off of the TV. Unlike filament shorts, control grid shorts can be eliminated, and it makes sense to try. The particles that fall into the cathode-control grid gap are usually very small, so they can be removed by burning. To do this, an electrolytic capacitor with a capacity of about 100 mkf, charged with a voltage of 450 V, is connected to the closed gap between the cathode and the control grid. The positive terminal of the capacitor is connected to the control grid, and the negative terminal is connected to the cathode. The discharge current of the capacitor is so high that the shorting particle evaporates. Sometimes, to eliminate a short circuit, you have to charge the capacitor several times and discharge it through a closed gap. If after several attempts the short circuit cannot be eliminated, then the kinescope cannot be restored.
Nonlinearity of the transfer characteristic (“gamma defect”)
Each electronic kinescope spotlight is characterized by the dependence of the beam current on the displacement on the control grid by a gamma characteristic. For a good transfer of all gradations of brightness, this dependence should be as linear as possible. Violation of the linearity of the gamma characteristic is called a “gamma defect”. A picture tube with such a malfunction produces oversaturated bright areas of the image and deep dark areas, and the number of grayscale levels is small. The image takes on a “silhouette” character. Contrary to popular belief that this fault is characteristic of gas tubes, it is actually caused by a defective cathode.
A “gamma defect” occurs when the central region of the cathode loses its ability to produce sufficient current due to damage to the emissive layer. The center of the cathode usually wears out earlier than the peripheral areas, because the edges begin to contribute to the beam current only in the bright areas of the image, and therefore retain their emissivity longer.
The appearance of a gamma defect when the cathode center is depleted
The only way to restore acceptable quality of operation of such a cathode is to reduce the absolute value of the bias voltage. Cathode control grid. This is done by increasing the DC voltage on the control grid, as a result of which the working area of the cathode in the initial section of the gamma characteristic expands. In color picture tubes with a planar arrangement of electronic spotlights and self-convergence, such an operation, as a rule, fails, because all three control grids are electrically connected to each other, and in order not to disturb the white balance, it is necessary to adjust the bias by reducing the DC voltage on the defective cathode. In this case, the video signal is limited from below, and the brightness of the light areas of the image is lost.
“Poisoned” cathode
The reason for reduced image brightness is often cathodes with a contaminated surface (so-called “poisoned” cathodes). Contaminants, which are usually the products of chemical reactions of the interaction of residual air in the picture tube container with the hot cathode material, act as a coating that prevents electrons from leaving the cathode surface. If contamination covers the entire surface of the cathode, the kinescope produces reduced brightness in all gradations. Often, contaminants are found only at the edges of the cathode, because they are not retained in the central part due to constant emission. As a result, with normal blacks and grays, there is a reduced brightness of the white areas of the image (as opposed to a “gamma defect”), which leads to a weakening of contrast.
You can try to restore a kinescope with such a malfunction. The recovery method is as follows: a reduced filament voltage is supplied to the heater, and a positive voltage of about 200 V is applied to the control grid. The cathode current should be limited to 100 mA, and the exposure time should be no more than 1.0 - 1.5 seconds per avoiding overheating of the cathode. The surface of the cathode “boils”, contaminants are torn off from its surface under the influence of a positive bias voltage and settle on the control grid, where they are no longer dangerous. This operation is repeated, if necessary, up to three times, and after each cycle it is necessary to control the cathode emission current, i.e., check how effectively the recovery process is proceeding. If after three recovery cycles the emission current does not increase to an acceptable level, this operation should be repeated with a cathode current of 150 mA
To control the emission current and to restore “poisoned” cathodes, it is convenient to use a device, the circuit diagram of which and design are described in the magazine “Radio” No. 10, 1991.
Temperature sensitive cathode
Some picture tubes produce a good image during normal operation, but exhibit a sharp decrease in emission if the filament voltage is reduced slightly. All cathodes reduce their emission as the filament voltage is lowered, but a good cathode produces many more electrons than are needed to form an electron beam. Therefore, a slight decrease in the filament voltage does not lead to a decrease in the beam current, since in this case the missing electrons are borrowed from the “reserve”. The smaller amount of emissive material, combined with a thin layer of contaminants, causes the cathode to deteriorate more than usual. Both of these factors reduce the number of reserve electrons and ultimately limit the current of the electron beam at normal filament voltage. Therefore, increased thermal sensitivity is a sure indication of a cathode malfunction.
You can also try to restore a cathode with increased thermal sensitivity using the technique proposed above.
Distorted color rendering
Distorted color problems arise when the three electronic projectors of a color picture tube cannot be balanced to produce normal tones of white and gray. Instead, the black-and-white portions of the image appear to have some color tint, and the colored portions have an incorrect coloration that cannot be adjusted correctly. Distorted color rendition is also possible with normal emission from all three cathodes of a color picture tube. CRT manufacturers specify that the beam current of any of the three cathodes must be at least 55% of the beam current of each of the other cathodes. An electronic spotlight whose current is below this limit is out of the range of permissible adjustments and does not make it possible to correctly set the white balance.
Secondly, even if a TV with raster correction is in service, then at the factory the memory is “written” using some average values and therefore, due to the same scatter in the parameters of the parts, sometimes the geometry is crooked and oblique.
Conclusions:
A) Roughly (approximately) the horizontal size can be rated B+, definitely not!
B) Adjusting B+ by size is not entirely correct!
Practice. I assembled a simple attachment device for measuring the rms value of the kinescope filament voltage. I took the Panasonic TX-21F1T NN as a standard. Attachment: from the filament, two wires to a bridge of 4 high-frequency diodes, the rectified voltage is smoothed out at 10.0X100V. Between plus and minus, a divider of two resistors with a total resistance of about 500 kohms. At one of the resistances at the limit of 10 volts I connect Ts43101 and select the resistances in such a way that 6.3 alternations of the standard correspond to 6.3V of the device. Accordingly, the set-top box together with the device does not reduce the heat and it is possible to estimate the LV spread in different TVs quite accurately. The attachment is mounted in a box, 4 wires come out of it. And let's measure the filament voltage on all repaired TVs in a row and also measure B+ on them. I checked more than 20 TVs, all B+ are normal, but the filament voltage is from 6.1 to 6.5 volts. (TVs FunaiMK7, FunaiMK8, Rodstar 570, LG chassis MC64A, etc. These TVs are 10 years old or more. All picture tubes are at least good in terms of emission).
Theory.
Service manual TV HORIZONT 63CTV671 chassis ShCTS-671M-2. Page 63. “Connect a voltmeter type F5263 to pins 1.2 of connector 1X5(A3) and check the kinescope filament supply voltage of (6.3±0.3) V. If necessary, adjust this voltage by closing (opening) the jumper 1SA12, 1SA13 . Opening the jumper reduces the voltage, closing it increases it;”
page 62 “6.2.3 Check the voltage +115 V (+140 V) between test point 1SA3 and the housing with a voltmeter. By rotating the slider of the variable resistor 1R804 on the color TV chassis, set the required voltage value +115 V, +140 V (depending on the type of kinescope) with an error of 5 V.”
Conclusion: The main filament voltage for this B+ model can be adjusted by jumpers.
Another service manual: HORIZONT 63CTV690 chassis ShCT-690.
Page 83 4.4.2.1 Check the +140 V voltage on the
output of the power supply. Rotating the variable resistor motor
R828 on the color TV chassis set the required value
voltage +140 V (depending on the type of kinescope) with an error of +-1.5 V.
Page 98-99 5.2.3 Adjusting horizontal and vertical scanning
- connect a voltmeter type F5263 to contacts 3.4 of the connector
X5(A3) and check the kinescope filament supply voltage
value 6.3 V. If necessary, adjust this voltage
voltage regulation 140 V within specified limits;
Conclusion: The main filament voltage for this model, B+, is regulated relative to it.
Another service manual ONYX 21 INCH (CHASSIS F2177HUE “HIS”) “+V voltage should be equal to +110 Volts +/- 0.5 Volts
6. check the kinescope filament voltage, it should be in the range from 5.7 to 6.6 volts. Typical = 6.15 volts”
Conclusions:
A) not all picture tubes have a typical NLC value of 6.3 volts, but for all of them the limit from 6.0 to 6.6 volts can be considered the norm.
B) With an NOC of 6.3 volts plus minus 5%, the plant guarantees the longevity of the kinescope, according to theory and tested in practice.
C) A B+ can only be assessed roughly based on NNK, unless the service manual states otherwise.
D) It is possible to regulate B+ accurately using the NOC only in cases where this is recommended by the manufacturer.
Further…
The circuit is designed in such a way that at B+ nominal or with a strictly defined permissible percentage deviation, the reception quality is optimal and the parts work in optimal mode (with the exception of factory defects, which are usually indicated in the bills of lading from the manufacturer).
In theory, all secondary power supplies are equivalent to NOCs. But part of the circuit is powered from the secondary circuits of the power supply and setting B+ via the NOC can lead to an undesirable (critical) change in one of the primary voltages.
Some power plants operate in severe thermal conditions. Changing B+ can lead to failure of the power supply.
So don't rush to turn the B+ knob with good intentions, because those intentions can lead to the worst.
Next, what if the individual entrepreneur is not regulated. Remake it to NNK standards? ...
There is another option to change the NOC. With a nominal B+. Selection of resistance in the divider circuit. But is it necessary to do this? Yes, in cases where the NOC is below 6 volts or above 6.6 volts. And in other cases? Have a resistor store for selection? Decide for yourself...
Kinescope, first identify the cause of the problem in its operation. The performance of the device is significantly affected by the occurrence of a short circuit between its electrodes, as well as reduced emission. Often the channel thread breaks or the cathode is peeled off, which ultimately leads to color distortion. Next, study the kinescope diagram specified in the operating instructions for your. In repairs, use the principle based on thermal training of the cathode, as well as shooting off spent particles located on its surface.
Firstly, having decided to restore the picture tube, first assemble the unit with which you can install the unit for your TV. You will need transformer T1, located on an old tube TV, diode VD1 or diode bridge, capacitor C1, two-section and three-section switches. From these parts, quickly assemble a special device with which you will repair your kinescope in the future, and then check according to the diagram whether you have assembled all the necessary parts correctly, and test the unit for its suitability.
Secondly, the method of restoring a kinescope involves supplying the unit with incandescence of various sizes in a clear sequence, which must be strictly observed. First, apply 6.3V heat to your kinescope and wait fifteen minutes to sufficiently warm up the device, then apply 8V heat for just two minutes, and then apply 11V heat for two seconds. Do not exceed the heating time, otherwise the kinescope may completely burn out instead of the necessary warming up. Carrying out the last step, apply a filament of 6.3V, and then briefly press the SA2 button so that the capacitor is discharged to the cathode modulator.
Repeat this operation several times, and after that connect the wires to the modulator and cathode, but remember that you no longer need to change the heat when performing this operation. It is better to switch the wires using a P2K type switch, which is usually used to switch the filament itself to the desired voltage. Remember that a restored kinescope will work for no more than a year, and its performance depends on both the type of kinescope itself and the resource remaining in it. If the kinescope is almost completely dead, increase the heat to maximum, but the unit itself may burn out.
The main malfunctions of the kinescope that you may encounter can be identified even before the start of operation. Moreover, this can be done at home using a special device.
Instructions
Before using the kinescope, it is advisable to check it. In the store, such testing is carried out on a special test bench. Often, many faults can be identified if you use a special device that is connected to the mains terminals. If you are checking a picture tube that is already inserted into the TV, remove the panel from the picture tube base.
A little about working with the device. For example, if you check the condition of the insulation between the filament and the cathode, then if it is good, you will see only one light bulb light up. And if there is a short circuit, two lights will light up.
If the insulation between the filament and the cathode does not reveal a fault, move the device switch to position 2 and determine the state of the insulation between the grid and the cathode. If the insulation is normal, you will see only one electrode of the neon lamp glow.
Typical faults of a kinescope include: broken filament; .loss of emission by the cathode; vacuum violation; phosphor burnout; break of the modulator output or cathode; short circuit between electrodes; failure of contact between the terminal of the second anode and the internal carbon coating.
If the filament breaks, the kinescope screen does not light up. In this case, troubleshooting must begin by measuring the voltage supplied to power the kinescope filament: it should be 6.3 V. The absence of alternating voltage indicates a malfunction in the power transformer.
When the cathode of the kinescope completely loses emission, the screen does not light up. With partial loss of emission, the brightness of the screen is insufficient and the focusing quality deteriorates. Additionally, as brightness and contrast are increased, the white parts of the image become negative. Partial loss of emission leads to a decrease in the beam current in the kinescope. This usually happens after long-term use, but can also appear in the initial period, especially if the TV is used incorrectly. The degree of emission loss is determined by measuring the cathode current. To do this, a microammeter is connected to the cathode circuit of the kinescope and the current is measured when the brightness control is set to the maximum position of the screen glow and with an image contrast corresponding to 5-6 gradations of brightness, distinguished on a television test table. Under these conditions, the cathode current must be at least 200 µA for 47LK picture tubes, 300 µA for 59LK picture tubes and 350 µA for 61LK picture tubes.
Violation of the vacuum in the kinescope is possible due to overheating of the electrodes or fittings when high voltages are applied to the electrodes. If the vacuum is partially broken, a milky coating forms on the inside of the picture tube neck, and a violet glow may be observed inside the neck. Partial disruption of the vacuum leads to an increase in beam current, deteriorating the quality of focusing. Troubleshooting is carried out by external inspection.
Burning through the luminescent layer of a kinescope screen usually occurs when the scanning is faulty, when the electron beam remains at one point on the screen for a long time. Burnout of the kinescope phosphor is also possible due to a frame scan malfunction, when a bright, focused horizontal line appears on the screen.
To prevent such burn-in, when repairing or checking the TV, do not allow a focused bright line or dot to appear on the screen.
When the cathode lead breaks, a dark or white blurred horizontal strip half the width of the screen appears on the kinescope screen or only part of the image is visible. The brightness of the screen is not adjustable or changes only slightly, and the contrast is insufficient. In such cases, the kinescope must be replaced.
If the modulator output is broken, the brightness of the screen cannot be adjusted, and the image quality is poor. In this case, you need to check the brightness control circuit, the cathode circuits of the picture tube and the contact of the lamp panel with the legs of the picture tube. In order to determine the cause of the malfunction, you need to connect a voltmeter to the modulator and cathode terminals on the kinescope panel. If, when turning the brightness control knob, the voltmeter readings change, and the brightness of the screen remains unchanged, this will indicate a break in the output of the kinescope modulator, and the kinescope must be replaced.
The cathode shorts to the filament spontaneously. It may appear and disappear periodically. Very often, when you turn on the TV, the kinescope works normally, and then after a long warm-up the cathode shorts. The image becomes blurry and its clarity is significantly reduced. Sometimes this defect can be eliminated? by lightly tapping the neck of the kinescope near the base.
However, after some time it appears again. The same defect can occur when a resistor connected in the circuit between the cathode and the filament breaks. If this resistor is working properly and the contacts in the kinescope panel are secure, it is necessary to replace the kinescope.
When the cathode is shorted to the modulator, the kinescope screen glows excessively brightly, and it is impossible to reduce the brightness with the regulator. This defect is also possible with a working kinescope, when there is a fault in the brightness control circuit. If, when you rotate the brightness control knob, the reading of the voltmeter connected to the sockets of the modulator and the cathode of the kinescope panel changes, then the brightness circuit is working. The presence of a short circuit between the modulator and the cathode can be determined using an ohmmeter.
If the contact between the terminal of the second anode and the aquadag (internal carbon coating) of the kinescope bulb is broken, with an increase in the brightness of the glow, horizontal lines in the form of a spark are visible on the kinescope screen with a faint crackling sound heard in the loudspeaker. With a significant decrease in the brightness of the glow, the defect becomes invisible. If sparking is observed inside the bulb near the anode terminal, then the kinescope is faulty and must be replaced.
Malfunctions in the kinescope circuits, according to external signs, manifest themselves in the absence of glow of the kinescope screen with normal sound, uneven glow of the screen, defocusing or distortion of the image.
The absence of screen glow is possible: in the absence of filament voltage or breakage of the kinescope filament, absence of constant voltage in the brightness control circuit, increase in the cathode-modulator voltage (the kinescope locking voltage), the absence of high voltage on the accelerating electrode and on the second anode of the kinescope.
Troubleshooting should begin by measuring the voltage on the filament and on the accelerating electrode. It is also necessary to correctly adjust the value of the kinescope locking voltage. It should be in the range of 20-70 V and depends on the position of the “Brightness” potentiometer. Next, check the presence of high voltage on the second anode of the kinescope, and if it is absent, check the operation of the horizontal scanning output stage.
An uneven glow of the kinescope screen is possible if the diode or other elements of the beam reverse suppression circuit are faulty, or if the deflection system is incorrectly positioned on the neck of the kinescope. If the diode in the flyback suppression circuit fails, the upper right corner of the image will be dark and the lower left corner will be light. In this case, there is no limitation of the positive emissions of pulses arriving at the modulating electrode of the kinescope when the reverse stroke of the vertical and horizontal scanning beam is suppressed.
If the deflection system of the kinescope is incorrectly positioned, the corners of the image are darkened. The deflection system must be pressed tightly against the cone part of the kinescope, and the defect must be eliminated.
Poor focusing may be a consequence of a decrease in the high voltage on the second anode of the kinescope, a decrease in voltage on the accelerating electrode of the kinescope, as well as malfunctions in the focus control circuit.
On TVs using electrostatic focusing picture tubes, there are several points for setting the required focusing voltage. The best focusing mode can be achieved by switching the focusing electrode to the 0, 200 or 600 V contacts.
Keystone image distortion occurs when there is a break in one of the horizontal deflection coils.
If there is a break in both horizontal deflection coils, the position of the trapezoid on the kinescope screen changes; at the bottom of the image the trapezoid is wider than at the top. Keystone distortion of the image is also possible when there is a short circuit in one of the sections of the low-voltage winding of the fuel assembly. This significantly reduces the brightness of the screen and the size of the raster. Sometimes keystone distortion of the image occurs due to the short circuit of part of the turns of the frame deflection coils. In this case, the position of the trapezoid on the kinescope screen changes: the left part of the image becomes larger in height than the right.
In order to determine which of the frame coils has short-circuited turns, you need to turn them off one by one and measure the vertical size of the raster. A smaller vertical raster size will indicate the presence of short-circuited turns in a given coil.
Image distortion, which has the shape of a “tie,” occurs when the ends of the frame deflection coils are incorrectly connected during the repair period, as a result of which the magnetic fields of the coils are directed towards each other and compensate each other.
“Barrel-shaped” image distortion is observed when the corrective magnets located on the body of the deflection system are incorrectly installed, as well as when a capacitor connected in series with the horizontal deflection coils is faulty.
If the corrective magnets are installed incorrectly on the deflection system, a distortion of the pillow-shaped image may appear. The horizontal and vertical lines of the image are curved outward at the edges of the screen. "Pincushion" distortion occurs due to the fact that the amount of beam deflection is not proportional to the amount of the deflection field in all areas of the screen. If by adjusting the correction magnets it is not possible to obtain a normal image, it is necessary to replace the deflection system.
"Reanimation" of black and white picture tubes.
A. RUBAN, Novosibirsk
Currently, television radio mechanics and some radio amateurs use devices to restore the emission of cathodes of picture tubes of the Quintal and PPVC types. They are quite difficult to repeat, and it is advisable to use them mainly to restore the operation of color picture tubes.
This is economically justified, which cannot be said about black and white picture tubes. Simpler devices and simplified techniques are suitable for them. The author of the published article shares his experience on these issues.
The fleet of portable and stationary black-and-white televisions produced in the 1980s - early 1990s remains quite large. Unlike picture tubes on color TVs, the service life of black and white picture tubes is usually longer. However, over time, the question arises about their “reanimation”, since buying a new kinescope for old TVs is already problematic.
In the literature, for example, in, methods for restoring the emission of color picture tube cathodes are repeatedly discussed. Based on them, knowing the electrical characteristics of black-and-white picture tubes, you can assemble a simple device for restoring emissions and their cathodes.
In those years, the domestic industry produced black and white televisions with a screen diagonal of 8 cm - models MAGNETON - MT-501D and ROVESNIK - up to 61 cm - unified models FOTON-234 (ZUST-61). The kinescopes used in them can be divided into three groups:
1) 8LKZ(4)B, 11LK1B, 16LK1(8)B with a filament voltage of 1.35 V and a filament current of 0.3 A;
The second group also includes imported picture tubes with screen diagonals of 13-35 cm, such as 5KTU4 (manufactured by SAMSUNG), 19SX3Y, 27SX8Y, 35SX1B (CRT) and others with a filament voltage of 12 V, installed in black-and-white TVs produced in the CIS countries and South-East Asia.
The pinout of their terminals in most cases also corresponds to domestic picture tubes of this group.
CRTs of the first and second groups are used in portable TV models, which could operate both from a built-in transformer power supply of mains voltage 220 V/50 Hz, and from an external source of constant voltage 12 V. CRTs of the third group are installed in stationary models with a unified switching power supply BPI-13 or similar.
The recommended method for “reanimating” these picture tubes consists of two stages. But first of all, disconnect all TV circuits from the kinescope panel. Restoring cathode emission at the first stage consists of “training” the kinescope cathode in the following sequence: first, the full filament voltage Un is applied for 5...15 minutes, then 1.5 Un - 1...2 min and, finally, 2 Un - 1 ...2 s. Next, the application of increased voltage values of 1.5 Un and 2 Un for the same periods of time is repeated two to three times. After this, the voltage of 1.5 Un is left applied.
At the second stage, a normalized dose of energy accumulated in the capacitor destroys the barrier layer on the cathode of the kinescope. This operation is carried out three to five times with an interval of 5...10 s. With a smaller interval, irreversible deformation of the electro-optical projector (EOP) of the kinescope is possible.
5...10 minutes after the end of the second stage, the filament voltage is reduced to nominal, and after another 5...15 minutes the kinescope is de-energized and connected to the standard TV circuits.
The filament voltage is supplied to the kinescope from the emitter of transistor VT1, the base of which is connected through a divider R2R3 to the rectifier output of the TV power supply. The lower terminal of capacitor C1 is connected to the cathode of the kinescope, and on probe X1 there is a constant voltage of approximately +300 V relative to the cathode. Resistor R1 limits the current through diode VD1 while charging capacitor C1. Low-resistance resistor R4 protects the kinescope filament from overload.
The device is assembled by mounted mounting on a circuit board, and the elements VD1, C1, R1 are well insulated, and the transistor VT1 is installed on a heat sink with an area of 60... 100 cm2. It is advisable to place the entire device in a dielectric housing.
Before starting “reanimation”, all the wires going to the TV are unsoldered from the X2 kinescope panel. The stabilizer and all other secondary circuits are disconnected from the rectifier of the TV power supply (if the power supply is transformer). In some TV models, the standard power filter capacitor is temporarily replaced with another with a rating of 470 μF for a voltage of 25 or even 35 V, if at idle the rectifier provides a voltage greater than the maximum voltage of the standard capacitor. Resistor R2 is selected based on the output voltage of the rectifier (usually 15...24 V) and the filament voltage of the kinescope.
On TVs with a switching power supply (ZUT-40, ZUST-61 and others with picture tubes of the 3rd group), remove the connector going from the power supply to the main board of the TV, connect the equivalent load to a 96 V voltage source - an incandescent lamp with a power of 60 W at voltage is 220 V, and the repeater input (collector of transistor VT1 and the upper terminal of resistor R2 in the diagram) is connected to a voltage source of +15 V. Do not forget to connect the filament terminal 2 of the kinescope through limiting resistor R4 to the common wire of the TV power supply.
Before connecting the emitter of transistor VT1 to the kinescope panel, markings corresponding to the values of 1, 1.5 and 2 voltage Un are applied to the variable resistor R3. In this case, between the emitter of transistor VT1 and the common wire, a resistor with a resistance of 4.7 Ohms and a dissipation power of 2 W is temporarily connected for the 1st group of picture tubes, 180 Ohms and 5 W for the 2nd group, 20 Ohms and 10 W for the 3rd group. th group. The capacitance of capacitor C1 is 0.5, 1 and 2 µF for the 1st, 2nd and 3rd groups of picture tubes, respectively.
Restoration of cathode emission is carried out according to the method described above, and at the second stage, probe X1 touches the terminal of the kinescope modulator on panel X2.
It is convenient to use the standard probe from the M-830 multimeter or similar. Diode VD1 - any with a forward current of at least 100 mA and a reverse voltage of at least 400 V, capacitor C1 - MBGO or MBGP for a voltage of 400 or 630 V. Transistor VT1 - any of the KT805, KT815, KT817 series.
As is known, the brightness of the phosphor of a kinescope is determined by the number and energy of electrons striking the phosphor. The number of electrons depends on the emission of the cathode, the speed (energy) depends on the voltage on the accelerating electrode of the kinescope. A simplified fragment of a typical circuit for connecting the accelerating and focusing electrodes of a black-and-white kinescope is shown in Fig. 2 (part numbering is conditional).
If you connect the output of the accelerating electrode instead of the right (according to the diagram) output of the resistor R1-focus regulator (marked with a cross) to its left output, i.e. directly to the output of the rectifier (VD1, C1), you can increase the brightness of the kinescope screen. In those TV models in which it is not possible to increase the accelerating voltage in this way, it is recommended to assemble a voltage doubler using a circuit similar to the anode voltage multiplier circuit. For the doubler, KD410AM diodes and K73-17 capacitors with a capacity of 0.01 μF for a voltage of 630 V are suitable. Sometimes it may be necessary to replace the filter capacitor in the accelerating voltage circuit installed directly on the kinescope panel with a higher voltage one.
If the above measures do not bring a visible result, there is one last way to briefly prolong the operation of the kinescope - increase the filament voltage first by 20%, and if the image intensifier is very worn - by another 20%. It should be noted that this measure only leads to a short-term positive result.
For picture tubes of the 2nd group, for this purpose, assemble a circuit similar to the voltage follower on elements VT1, R2, R3 in Fig. 1. The TV can only operate from a -220 V/50 Hz network.
For kinescopes of the 1st and 3rd groups, the filament voltage of which comes from a line transformer, an additional step-up transformer is made on a ring of M1000NM ferrite. The primary winding of the transformer contains 8 turns, and the secondary winding contains 10 or 12 (if the image intensifier tube is very worn) turns of any insulated wire with a diameter of 0.3 mm. The primary winding of the transformer is connected instead of the standard kinescope filament connection, and the voltage from the secondary winding through a resistor with a resistance of 1 Ohm and a dissipation power of 0.25 W is supplied to the kinescope filament. The standard size of the transformer ring for picture tubes of the 1st group is K10x6x5, for picture tubes of the 3rd group - K20x10x5.
After carrying out all the above operations, you may need to slightly adjust the focusing voltage of the kinescope.
To “reanimate” picture tubes of the 1st group, you can use the “exnpecc” method, tested by the author back in his student years, when only the minimum necessary components and devices were at hand. First, as always, unsolder all the wires from the kinescope panel. Then, a voltage of 1.5 V is applied to the kinescope filament from a “fresh” AA-size element. After 5 minutes, the next operation is performed. First you need to prepare a power cord with a plug at one end. One of the two wires at the other end of the cord is soldered to the cathode terminal on the picture tube panel, and the end of the other wire is tinned. Carefully holding this end of the wire by the undamaged insulation with one hand, with the other hand plug the cord plug into a power outlet (-220 V/50 Hz), and with the tinned end, “one-touch” the output of the kinescope modulator twice and disconnect the plug from the outlet. 10 minutes after this operation, remove the voltage from the kinescope filament.
Despite the primitiveness of this method, the kinescope was reanimated quite well. During at least one year of further operation, there were no complaints from TV owners.
Literature
1. Adamovich V.N. et al. The second life of color picture tubes. - M.: Radio and communication, 1992.
2. Elyashkevich S. A. Color TVs 3ust. - M.: Radio and communication, 1990.
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