Re: gEDA-user: Any TV repair gurus lurking?

[Peter Clifton <pcjc2@xxxxxxxxx>]

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!)



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