My sisters TV had no speaker sound, a bad tuner and the thing was loath to turn on. Found out about the smps diodes and caps. Fixed that. Came on every time, and stayed on. Excellent picture using a VCR as the tuner. Sound available from the earphone connection, hooked to input of stereo. Found the voltage from U3101 not enabling the audio amp U900 at pin
- Trying to probe, I crossed two terminals, and it went into runaway and fried. Replaced with new audio, and lifted a resistor R901 to enable the audio amp. Got the THWACK in the speakers at power up, but worked other than that. Set on shelf to return to my sister, but our TV died, so put it into use. Worked for a few weeks, then would not turn on. I pulled the power connector to the audio board, and it came up. Replaced audio chip, and re-installed pulled resistor to pin 3. Found damaged trace between R908 and Q601, and jumpered using blue wire. Reinstalled chassis. Now, sound came up, no THWACK, went off fine. No video. Have OSD, have sound. Channels change, onscreen displays jump a bit vertically switching from 90 to 91 to 92 to VHF, as they should. Select out, both audio and composite, work as good input to another set. S-video input does not work, nor do the composite video inputs.
I think I fried something on the comb board, as the chroma is a straight(about 9 volts) line on the scope coming from pin 8 heading to jungle U1001, the luma out on pin 7 looks good. I errantly used the chopper heatsink to ground the jumper wire when I discharged the CRT. Only later to read, in my native ENGLISH, " heatsink is not grounded ". Ooops dummy!
Is there any possibility that is is not the COMB board? The raster is black, but HV and OSD are there. 238 Volts on the cathode drivers (HI?) with no picture. Other voltages I have checked seem good. Anyone have a clue? Spare COMB board? Is there any possibility of one of the COMB diodes shorting or is it the M50572APS chip? I don't have any schematic for the COMB, but plan on removing it to examine for obvious 'smoke escape spots'.
thanks for reading of my mistakes... tom