On 2/21/2016 9:34 AM, Cursitor Doom wrote:
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!!!

Pulling V1812 lets you see the clean output from the driver chip without
all the crap feedback from the transformers. Your frequency looks good.

I got the same crap and ringing/distortion on my PSU without a load. Put
a load on it. switchers don't work off load.