Greg Mayman wrote in a message to Roy J. Tellason:

 -=> Roy J. Tellason said to All
 -=> about "POWER SUPPLY" on 10-25-03  04:06.....

 RJT> Beats the heck out of me what parts I might be wanting to look at
 RJT> next,  to the extent that I can with my eyes in the shape they're in
 RJT> these days. 

 GM> There should be a couple of large capacitors rated at about 400v,
 GM> IIRC these should have about 150v on them when the unit is
 GM> powered up. Discharge these first before continuing with tests!

Yes...

 GM> Some of these power supplies have a mains fuse on the PCB. While it
 GM> appears at first to be a damn stupid place to put a fuse, it does
 GM> prevent someone replacing it with one rated for automotive use (10A
 GM> or higher).

That's in there,  and it's good.

 GM> You should first test for continuity from mains input through the
 GM> power switch and rectifier diodes to the big capacitors.

The fuse is good,  the thermistor is good,  and the bridge rectifier is good.

 GM> Check the two transistors that feed power from these caps to the 
 GM> transformer.

They check out good as well.

 GM> Note these are high voltage transistors, usually rated at 600v 
 GM> peak if you are thinking of replacing them.

At least!

 GM> A digital voltmeter usually has a diode test position which is 
 GM> fine for checking the forward and reverse voltage drop through the 
 GM> junctions. One of these transistors may have gone open circuit.

Nope.  Unless I'm getting a spurious reading from them still being
in-circuit. I didn't get anything suspiciously low,  though,  just normal
transistor type readings...

 GM> Connect power, measure voltage across the big caps. Should be about
 GM> 300v total IIRC. Check for high frequency signal from the power
 GM> transistors to the transformer - caution: HIGH VOLTAGE.

Somewhere I have an isolation transformer,  but having this board flopping
around loose while powered up doesn't have much appeal to it.  I've put off
that step until I can come up with a comfortable way of dealing with this. 
:-)

In the meantime,  if I can get some better lighting over here and maybe
better magnification,  then I'll have another look at it,  and test some of
the smaller passive components over on the primary side.

 GM> Beyond that, you're getting deep into more or less unknown 
 GM> territory.

It's known to some.  I think what I've got going on here is a startup
problem. I've read of some folks who have found similar problems to be
caused by a resistor (!) going bad,  usually changing in value way upwards
of what it's supposed to be.  What's on that board is quarter-watt and
smaller (!),  so although I can look at it and see that it's a resistor, 
that's about as far as it goes at this point without some further
assistance.  I can see that there are electrolytics,  resistors,  and
glass- and epoxy-cased diodes,  can even see the polarity band on those
last,  but that's as far as it goes.  I can't read the color-codes on the
bloody things any more...    :-(

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