On Thu, 2007-12-20 at 20:46 -0500, Stuart Brorson wrote: > 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 > Dinosaurs eh?.... Noah was my regular customer... Never got that depth sounder going for him... Might have missed that mountain if I did...
also do a visual of the electros around the vert linearity/feedback area. Look for a convex top (indicating excess pressure). If the top is not flat then it has probably blown out electrolyte. If there are any N.P caps there I would check them for esr. -- Greg (who also spins anti-clockwise) > > 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 > > geda-user@moria.seul.org > > http://www.seul.org/cgi-bin/mailman/listinfo/geda-user > > > > > _______________________________________________ > geda-user mailing list > geda-user@moria.seul.org > http://www.seul.org/cgi-bin/mailman/listinfo/geda-user -- Greg Cunningham mailto:[EMAIL PROTECTED] _______________________________________________ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user