b wrote:
On 11 nov, 08:37, Sylvia Else wrote:
Sylvia Else wrote:
I bought this on Ebay for $5.50 on the off chance that I could fix it.
It was described as having lost picture with a "pop", and with the
observation that a TV repairman said it sounded like it could be a power
supply issue.
I've determined that the sound works OK, as does the tuner and video
signal stage - it outputs the composite video on an AV out socket.
It's clear what produced the "pop" noise.
http://members.optusnet.com.au/sylviae/tv1.jpg
http://members.optusnet.com.au/sylviae/tv2.jpg
Presumably this diode shorted out. It's on a board close the EHT circuitry.
But what are the chances that that's all that's wrong with it? Just
getting the board out to gain access to the underside will be a fairly
major exercise.
Sylvia.
I've given up on this anyway. Having run out of other ideas, I pulled
apart the box mounted on the neck of the tube, to see whether the
reported "pop" might have come from there. Nothing of note inside,
except yet more large heat-sinks. Anyway, I decided that putting it back
together again was going to be more trouble than it's worth. So it's off
to the tip tomorrow.
Sylvia.
you shouldn't give up yet.
Any static on screen?
what happens if you raise the g2/screen pot on the line o/p
transformer?
have you got volts on the RGB o/p stage on the CRT neck pcb?
have you checked for open resistros in the frame circuit feed (very
common 'black screen' cause)? have you checked components in the line
driver cct?
these are all fundamental first steps - I think your troubleshooting
has not been very systematic if you haven't done 'em!
-B
The switching transistor for the EHT transformer has no base drive. I
traced backwards through a transformer, another bibolar transistor, a
pair of FETs, a pair of bipolar transistors and ultimately reached two
outputs from the programmable LSI circuit. So the reason there was no
EHT was that the outputs from the LSI were unchanging. I surmise that it
had probably detected some fault, and disabled the EHT for that reason,
but since it's programmable, I have no way of determining what it might
be objecting to. I couldn't find any dead transistors, or capacitors
that were evidently faulty, and the low resistance resistors that I
measured were all within tolerance. Nothing had obviously burnt out.
Anyway, it's in the car now. Given how heavy it is, there's no way it's
moving from there other than at the tip.
Sylvia.