29 Apr
2017
29 Apr
'17
10:59 p.m.
On Sat, Apr 29, 2017 at 7:36 PM, Aaron Jackson via cctalk
<cctalk at classiccmp.org> wrote:
Is this with the transistor soldered to the board or removed? If the latter then
the transistor is shorted base-emitter. If the former then you are measuring
the resistance of L200 and the secondary of T201 (horizontal drive transformer)
in seroes which will be essentially zero.
Since it
doesn't smoke, I'm thinking the horizontal sweep
transistor may have gone out. It may have shorted, which
then may have burned up the primary winding in the flyback
(if left on long enough). I'd check that transistor for a
short, and then you can trace a few traces to identify the
primary terminals on the flyback and see if they are an open
circuit.
Hmm, not good news. zero ohm between pin one and three of the transistor
you mentioned. To be fair the board around it looks a little brown, but I assumed this was just because it would have got hot.
Could replacing
this cause damage to the flyback? I seem to have a low resistance on
what I think is the primary coil.
Most flyback windings have a very low DC resistance. In any case the most
common failure is a short between a couple of turns of such a winding which
will ruin the AC performance of the transformer but have almost no effect
on the resistance. That's why you need to test such a transformer with a
ringing tester, not an ohmmeter.
-tony