Maintenance of special faults of Panasonic color T

Maintenance of special faults of Panasonic color TV

I. grating fault of M11 color TV

a Changhong cj-37a color TV (M11), with normal startup sound, there is a broken horizontal line in the middle and upper part of the grating, below which is the compressed and disconnected image of the lower half, and there are two gratings when there is no image, as shown in Figure 1

according to the preliminary judgment of grating phenomenon, the fault is in the line field part. The voltage of the output part of the measuring field, Q402 collector 50V, q403 base 0.45V, emitter 0.1V, all deviate from the normal value. It is estimated that Q402 and q403 are abnormal, but their bvcbo and BVCEO are qualified. The difference in magnification between the two tubes is too large. The magnification of Q402 is 100 times and that of q403 is only about 50 times. Replace q403 with a 100 times one, but the fault remains the same. From the above measurements, it is also suspected that the field excitation signal is abnormal. There is no problem with the peripheral components of ic501, and it is invalid to replace ic501. After that, the voltage of each pole of q401 was measured. The collector was 41.2v, the base was 26.2v, and the emitter was 26.3v, which deviated greatly from the normal value. However, q401 is also normal, and no problem can be found by checking the surrounding components. Later, we broadened our thinking and considered that the voltage of the field output part was low, which should be 57V, but now it was only 50V. Since there was no problem found everywhere in the field output part, could it be caused by the power supply department 5. The ring stiffness tester should keep the jaw of the fixture or the relatively sliding surface of the fixture clean? Check that D804 and r805 are also normal. Finally, measure that c809 has basically no capacity and becomes a leakage resistance. After replacement, the voltage at all parts of the field output part returned to normal, and the fault was eliminated

II. M12 machine center color TV grating failure

a Panasonic tc-430d color TV automatically protects itself about an hour after cold startup, and the grating disappears. Turn up the volume, although there is no accompanying sound, there is still noise. Turn off and cool down for a while, and then turn on and return to normal, but the working time is short and the above phenomenon is repeated, and the working time is shorter than once, resulting in no grating after turning on

when the grating disappears, the measured ic501 ⑤ pin is 0.75V and greater than 0.7V, indicating that its internal protection circuit has acted. At this time, the measured collector voltage of q801 is 15V, which means that the protection circuit action is initiated by q801. At this time, ic501 ⑥ pin is 0V and the line push signal is cut off. Check the line output stage, line push stage, + 12V generation circuit ic802 and picture tube circuit, and no problem is found. The measurement line output tube and line push tube are also normal, and it is useless to replace ic802 and line output transformer. Later, q801 was welded down, and the above fault phenomenon was still repeated when the machine was turned on in cold state. When the fault occurred, the ⑤ pin of ic501 was measured to be 0V, and the ⑥ pin was 2V, indicating that the internal protection circuit did not act, and there was already row push signal output. The base voltage of q501 push tube is 0.4V, and the collector is 80V, which works normally. The base pole of q551 measuring tube is 0V, indicating that the driving signal has not been added to the tube. Before measuring r560, it was also 0V, indicating that the root cause of the fault was inside the secondary of the line pushing transformer. After the temperature rose for a period of time after starting up, a thermal short circuit occurred, so that the line pushing signal could not be added to the line tube and the line tube stopped working. At the same time, the + 12V generation circuit ic802 has no 12V output, causing D502 breakdown, making q801 conductive, and starting ic501 to cut off the line driving signal by the protection circuit. After replacing the row push transformer, the fault is eliminated

III. m15l mobile color TV III has no fault. A Panasonic tc-2186 color TV has a standby light on after it is turned on, and the manual remote control fails, with no light, no picture, and no sound. It is a common fault of the machine

unplug the standby light plug-in E4, turn on the machine, the image and sound return to normal, and the local keys and remote control can also operate normally. Because the standby light can be lit, it indicates that the standby light itself is normal. The problem lies in the microprocessor circuit, standby circuit or remote control circuit. This part of the circuit is shown in Figure 2. Restore the standby light, turn it on, measure 113v without output, and measure the standby power supply + 5V, which is only 3.2 ~ 3.8V and unstable. Obviously, the microprocessor cannot work normally. This voltage is applied to the base of the main power control tube q811, and q811 is turned on, forcing ic801 to have no 113v output. Disconnect the standby control tube q814 and force the standby power supply + 5V to work. The negative terminal of d814 is measured to be only 3.2 ~ 3.8. Therefore, the performance of Corvette C7 will be improved by 1 floor v. the emitter voltage of overcurrent protection tube q812 (on r815) is measured to be 0.64v, which proves that the standby power supply + 5V is overloaded. Disconnect the negative pole of d814, that is, disconnect the + 5V load, measure its positive end + 5V and return to normal, indicating that the + 5V standby power supply itself is normal, which further proves that our judgment is correct. It indicates that the load is so heavy that the overcurrent protection tube q812 is in the conduction state of different degrees. Control the emitter voltage of standby power supply adjustment tube q810 to reduce its output voltage to 3.2 ~ 3.8V. Next, cut off the load of ＋ 5V standby power supply step by step to judge the fault point. There are three loads, namely ic1106 reset circuit, ic1102 microprocessor circuit and remote control receiver circuit. Among these three channels, it is most convenient to cut off the remote control receiver. First restore the negative end of d814, and then unplug the E1 plug of the remote control receiver. When the machine is turned on, the image and sound are normal, and the panel buttons can operate normally. This indicates that there is a problem with the receiving head. Replace it and eliminate all the faults

on the contrary, why did you unplug the standby light and take the receiver with you, the image and sound are normal, the panel keys are normal, and why is the remote control normal? Isn't there a problem with the receiver? The problem is, after unplugging the standby light, the main power control tube q811 base display electronic universal experimental model adopts the LCD display measurement system, and the + 5V standby power supply cannot pass through. It is at zero potential, q811 is cut off, ic801 can output 113v normally, and the TV can work normally. The host + 12V can be added to the input end of the ① pin of ic1105, and the ② pin can output + 5V, so that the microprocessor, reset circuit, receiving head, etc. can work normally. The decisive factor for normal operation is the host + 12V power supply provided by ic802 and the host + 5V power supply provided by ic1105. Its capacity is sufficient for the normal operation of key curve detector and other equipment and the measurement range that can maintain the best accuracy. However, this special case is that the receiving head is not completely short circuited, only a certain degree of leakage, but the standby power supply + 5V capacity is limited, which is not enough to bear. Therefore, as long as you bring the standby light, you will bring the receiving head. Its slight leakage is enough to reduce the standby power supply + 5V, so that the standby power supply cannot work normally, the main power supply cannot be established, and the remote control will naturally fail. This case of failure is difficult to understand, which is the reason

IV. mx-2 mobile color TV three no faults

a Panasonic tc-25v40rq 25 inch color TV, boot three no, and the power indicator is not on

after inspection, the AC fuse is intact, but P82 ① pin has no 5V output, and P83 ⑥ pin has no 142v (＋ b) output