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.
Cool, thanks... I'll see if I can borrow a scope tomorrow before the lab shuts for the holidays. I'm getting a scaredy-cat in my 20s.. don't like working on live equipment much any more (not TVs anyway.. very difficult to probe things safely in the jungle of wires / boards propped up), and its always tricky to get at the right caps to discharge. Seems like something I need to do though. If I can manage, I'll leave if off for a while, hook up the probes (might have to borrow an isolated differential probe), and then power up with everything attached. I remember dismantling a big TV to fix once at secondary school in our IT department (replacing a soldered on settings battery). I remember reaching for the anode cap to pull it off. I'm not sure what pulled me back as I started to peel the rubber (might have been the hairs on my hand or something), but I suddenly decided / remembered to ground it first. (Draw nearly an inch long spark... my fingers hadn't been much further away!) That TV taught me two important lessons: 1) Always ground / short things if they had a chance of being live 2) Take notes what plugs / wires went where... the manufacturer had re-used a connector type for two plugs. I swapped them (connecting a deflection yoke across a PSU.. blowing a rectifier diode). The set went to a proper repairer after that - he confirmed my juvenile diagnosis of blown diode, and the set was fixed ;) After that I stuck to fixing computer monitors for a while.. nothing sweeter than free hardware you fixed yourself. I could scrounge old SLOW reject computers at the time, but working monitors were almost never thrown out. -- 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