On Sat, 20 Feb 2016 15:45:34 -0500, JC wrote:

Have you posted this before on another thread related to this? Either you
have or it's deja vu. Sorry if you did, I didn't note it properly.

I managed to find a PM3264 PSU to try out.

Unloaded it squeals as expected so I tried a makeshift load with what I
had lying around, 6 x 470R 5Watt w/w resistors.

You can pull one of the connectors out of the scope for a connection.
(See photos)

Yeah, those Stocko connectors. On another Philips manual I have for a
different scope, they actually publish the proper values for a dummy load
which would be really helpful to have on the current problem I face.

Just for fun (and I'm running this off an isolation transformer), pull
V1812 and scope T2 with T1 as probe ground. you should see a nice drive
waveform for a few seconds and you can check the frequency is 20KHz.

Not sure why you say pull V1812, but here's the waveform I got between
those two points when I did this test a few weeks ago:

https://www.flickr.com/photos/128859...n/photostream/

But then it goes downhill. Here's V1812's C/E junction:

https://www.flickr.com/photos/128859...n/photostream/

And the B/E junction of the main chopper transistor:

https://www.flickr.com/photos/128859...n/photostream/

Not surprising it doesn't work properly with control voltages like that!!!