Fault phenomenon: Konka color TV P21SK177 after the lightning strike three no-fuse fuse is good, the field effect transistor is normal, 16846 13 feet have a slight swing. Because it is a lightning striker, 16846 is very likely to be bad. After checking the sampling circuit for no abnormality, after changing to 16846, B+ voltage is 105V. The power indicator flashes and it will be off. This should be the startup phenomenon, but the line does not work, the TV has Slightly snoring (then thought that the high pressure package was issued).
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It is suspected that there is a short circuit after the lightning strike, and there is no short circuit in the secondary groups of the test transformer. The voltage of each chip is measured: 61 feet, 56 feet, 54 feet 3.. 3V. 14J feet, 39 feet 7.7V (lower 0.3V, because only a few volts, I use a mechanical watch, the table is not necessarily very accurate, so I did not care).
Test 2408 8 feet 5V, 5 feet, 6 feet voltage 2V swing, after changing the memory, the fault remains.
The power-on indicator can flash, and the 39-pin has a voltage, indicating that it is powered on, and the CPU part of the chip should be normal.
The line of the test pushes the voltage of the C pin to only a few tenths of a volt, at a saturated state, sometimes it can rise to a few volts, and quickly retreats. It seems that sometimes there is a line oscillating pulse, the lightning strikes the CPU part of the super chip, and the video conversion part is bad, but the line is oscillating. Some bad memories seem to have not been encountered before. There is no such chip at hand, and the repair has no clue.
Rest a bit, re-adjust the idea, the voltage of 39 feet is provided by 7808, the voltage should be 8V, the voltage of 1 foot of 7808 is only 9.5V, it should be 12V, obviously low, the field power supply plus or minus 12V is just the voltage of the circuit icon note The sound voltage is 20V, the circuit icon is 18V, B+105v, and the voltages in the latter groups are also low. Adjust the sampling potentiometer to adjust B+ to 120V, and the voltage of each group also rises to 1.8V. The fault is still the same.
B+ has been adjusted to 120V, 7808's 3 feet 7.9V or so should be very close! But the 1808's 1 pin is still only about 11.2V, the difference is about 1V, will this group of 12V power supply load have a slight short circuit? But this group of 12V is connected to the sampling circuit and cannot be easily disconnected. So decided to try it with the power module.
The short circuit pushes the transformer secondary, removes the FET, and connects to the module. Adjust the B+ voltage to 115V, disconnect the line to push the transformer secondary, “哧†a high-voltage start sound, the TV appears a grating, and the video is normal. It can also be played by adjusting the B+ voltage to 100V. Prove that the TV cold part should be no problem.
The module can be removed, the FET is soldered, and the fault is still the same.
The module can be placed, the fault should be in the power supply, and the power supply is re-examined. Some diodes that are easily damaged by lightning are normal. Will it be a problem with the 16846 soldering (in fact, it has been checked with a multimeter), pick up the magnifying glass, and observe it carefully. Found 1846 of 16846, and C917 of 2 feet, C913 seems to be a little off-weld, can not be seen carefully, re-weld, the test machine is normal.
In order to find out which capacitor is desoldered, the C913 is re-welded, and B+ has no output. The above failure occurred after welding C917. (Probably when I removed 16846, I encountered the C917 causing desoldering). Because it was a lightning striker, after switching to 16846, B+ had an output, neglecting the fault point and taking a detour.
To add, after this TV is repaired, I have measured 5 feet of 2408. When the voltage of 6 feet has a signal, it is about 2V. When there is no signal, it will swing around 2V. This voltage should have been around 3 to 4V. This is why I mistakenly believe that the fault is One of the causes of misjudgment on the CPU or memory.
