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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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Hi all,
I did a little searching of the group and have read the posts and replies for a couple of similar situations. I Would like to add some notes of my conditions before I make my next move. UNIT: Sansui COM 0952 (Funai, Symphonic variant) Initial Problem: Power light comes on, but no startup. Troubleshooting: Replaced 2200uF 105deg electtrolytic on 11.3V supply. Result: TV powers on with video and sound, however, during startup, the CRT goes from black to White (is the correct term "full brightness?" then "fades down" into picture. Picture is nice and clear, colors are good, contrast is actually really good. Basically, it seems to me that the CRT is OK. This set has a 125V B+ line which I think is created via the flyback from the 11.3V supply. Anyway I monitored the B+ line and it is about 122V during startup. As the CRT comes into its "full white" stage, the B+ climbs to about 123.2V. Now as the CRT "fades down" down into the picture the B+ is simultaneously rising to the 125V. I Checked the electrolytics and rectifiers for the FB scan derived and power supply circuits and everything seems ok. When I adjust the Screen (brightness) Pot on the flyback I get a full raster like i should however when I turn it all the way down I cannot "dim out" the picture on the CRT. It just gets a "milky-white look to it". The focus works fine. I suspect the flyback may be bad (or more correctly-weak?). Perhaps the internal resistor network is failing or the HV diodes in the multiplier may be leaky. Anyone had a similar problem with these that turned out to be the flyback? The reason why I asked is that I repaired another sansui combo with the same problem, same bad capacitor and now the same acting CRT startup situation. It looks like a trend and because there is no separate B+ supply (I assume because of the AC/DC operation). I suppose it could be a scan derived supply pulling the B+ down, but I doubt it because of the unusal Screen control operation and the fact that the Flyback is having to help generate its own B+(It think...). (Excuse me if I am wrong here) A guess would be that as the flyback weakens it ceates a huge startup load for the 11.3V supply which eventually fails the Electrolytic? Any help would be appreciated. John Z. |
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