On Wed, 17 Feb 2016 10:05:38 -0000 (UTC), Cursitor Doom
wrote:

On Wed, 17 Feb 2016 01:09:27 -0500, legg wrote:

C1827 is 'Select On Test' (SOT) to trim some operating parameter in the
functioning unit - possibly the HT tolerance under load or even just
display noise. You'd need a manual to figure this out. The more often
you mention the actual model number (PM3264 ?), the more likely it is
that you'll get someone to cough one up. It's $20 from jetecnet.

Ceramic disc caps of this size were typically 500VDC rated at that time.
Only smaller square plate types were less (and some offshore stuff).
Lower voltages will generally be marked as such, or colour coded for
identification in the mfrs spec sheet.

You still haven't identified the diode substitutions made in the
primary, or reported on secondary winding amplitudes loaded/unloaded.

You still need to report IC pin3 voltage when loaded. (it is reported as
normal, when unloaded, indicating a regulated condition exists.)

RL

Thank you for your observations.
I can only reiterate that testing under mains power is not practically
possible, loaded or unloaded, given that I only have about 15s before
that power resistor starts to burn up in either case. I really have to
try to crack this by other means.
There is no way on earth the subbed caps are anywhere remotely close to
500V rating; they'd be lucky to withstand a tenth of that. I'm going to
pull them out later today and replace them with a properly rated part
then I'll scope for noise again. I suspect it's this noise, fed back,
that's causing the primary circuit to fire falsely regardless of the
signal from the pwm chip; the excess switching energy therefrom showing
up as excessive heat in the power resistor which is only rated to
dissipate the *expected* switching energy from a properly functioning
primary circuit. Anyway, we'll see....

Your concern for this resistor's health is touching, but it really is
misplaced, as the part is easily replaced, relocated, temporarilly
beefed up or whatever.

If you know what you want to do, in 15seconds, you can do a lot,
particularly if you're prepared to repeat the process at intervals,
until all the necessary info is accurately recorded.

RL