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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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KP48S65 Horiz sync problem
We have a word for problems like this one, but I'll refrain from using
it in public. On a high brigthness signal it jitters about an inch back and forth. On a test pattern there is a slight wave in it, but it is hard to see on normal video. That is so slight that it almost could be left alone, but it's surely related to the jitter. I changed C 338 which is the low freq portion of the AFC filter network. Also changed IC 301 to no avail. I also bypassed C333 which didn't do anything. I see pin 38 is also fed by Q 314. It seems to get an inverted ABL signal there. To eliminate that as a suspect I disabled it temporarily by shorting Q 314 E to B. Still doing it. Looking further, with the spec sheet for the CXA2025AS I find pin 37 is called L2LFIN. The spec sheet says to bypass it and that you can use DC to shift the H sync phase. I have also bypassed that with a .01, which is plenty since it is fed through a 470K resistor (R 375). There is also something not quite right abut the picture. It looks like the video is slightly clipped on the whites. Naturally I checked the signal at the HSIN pin 44. From the sync tips to the top of a staircase waveform it is exactly 2.0 V P-P, as called for in the print. Anything you might have on this would be greatly appreciated. JURB |
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