Back when dinosaurs roamed the earth, I used to fix TVs in a TV repair shop. Maybe I remember some of what I knew then, but the jury is out on that one.
I'd take a look at the driver transistor for the vertical oscillator, or any of it supporting components. It sounds like the vertical sweep osc is having a hard time producing a nice, solid saw-tooth wave. Putting a scope probe on it would be a good idea. FWIW, the horizontal oscillator is often the culpret in these bad sweep problems, so take a look at it too, using the scope. HTH, Stuart On Fri, 21 Dec 2007, Peter Clifton wrote: > Hi, > > I'm fixing (or trying to) a TV for a friend, and wondered if anyone had > any wisdom relating to the following symptom. > > This is a Sony BE-3D chassis, and exhibits an intermittent fault. When > its doing it, the picture is still visible, but collapsed (jitteringly) > upwards towards the top of the screen. It doesn't stay collapsed for > particularly long. The sections of image which collapsed upwards also > narrowed horizontally, leading to a tapered looking screen > --------------- > |\ /| > | \ / | > | \_______/ | > | | > --------------- > > (Although this diagram probably exaggerates it somewhat). > > None of the obvious supply caps tested for bad ESR on my meter (main PSU > cap, the various secondary side PSU caps including B+, the flyback > derived 200V supply etc.) Even when raster / scan has been lost > completely, sound works fine. At one extreme I saw in person today, the > vertical collapse left three horizontal lines (R,G,B) separated by an > inch or so on the screen towards the top. No picture was visible (and I > turned it off). > > I know this set has a common fault with flyback transformers failing due > to internal arcing. I almost convinced myself this was probably the > case, but now I'm not so sure. Could it cause the symptom? (It usually > supposed to trip the sets overcurrent protect on the B+ line and shut > down H drive, throwing the set into standby though - which it didn't > seem to do for me today). > > Unfortunately its been several years since I last fixed a TV, and I > don't have my handy box of bits for insulated prodding / light-bulb > inserting / freezing / HV testing. I don't even have an oscilloscope > here (although I could borrow one from the lab). I'm working with > multimeter and ESR meter. I do have the schematics and service manual > though, which is a big plus. > > Best wishes, > > -- > Peter Clifton > > Electrical Engineering Division, > Engineering Department, > University of Cambridge, > 9, JJ Thomson Avenue, > Cambridge > CB3 0FA > > Tel: +44 (0)7729 980173 - (No signal in the lab!) > > > > _______________________________________________ > geda-user mailing list > [email protected] > http://www.seul.org/cgi-bin/mailman/listinfo/geda-user > _______________________________________________ geda-user mailing list [email protected] http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
