exxos's Atari, Amiga & retro forum

Steve wrote: 28 Apr 2023 10:08

rubber_jonnie wrote: 27 Apr 2023 20:16 Usually when I see weird results it's the probe GND that's the issue.

Make sure the leads gnd leads are good.

Maybe I need to connect to shield... Amigas have gnd/shield seperate, all these measurements were connected to gnd.

@rubber_jonnie I mentioned this early on in the thread. I tried both GND and Shield with similar/identical results.

Steve wrote: 04 May 2023 17:21

Steve wrote: 28 Apr 2023 10:08

Maybe I need to connect to shield... Amigas have gnd/shield seperate, all these measurements were connected to gnd.

@rubber_jonnie I mentioned this early on in the thread. I tried both GND and Shield with similar/identical results.

Ahh, ok, I must have missed that :dizzy:

@Steve I did a spot more testing this morning and the conclusion was that I don't see anything on the pins of my power plug with the PSU unplugged, just a flat line.

The only way I could provoke anything odd was to add a 1 foot long clip lead to my scope probe and leave it unconnected, then I could pick up 50Hz, but even with the clip lead, I saw nothing on the PSU power pins with it unplugged.

I can only suggest you are near something that your scope is picking up with the PSU as an aerial, but what I do not know.

@rubber_jonnie
Thanks for doing that... my next idea is to do the obvious: test a known-good Atari PSU I've previously worked on, just to see if I see the same weirdness. If I do I'll try and get some kind of isolation device for my scope, like the kind in that video I posted. I don't have much choice about where my equipment is anymore, or the other devices connected near it. So I either find a way to mitigate the problem, or just stop using it altogether.

Steve wrote: 05 May 2023 12:46 @rubber_jonnie
Thanks for doing that... my next idea is to do the obvious: test a known-good Atari PSU I've previously worked on, just to see if I see the same weirdness. If I do I'll try and get some kind of isolation device for my scope, like the kind in that video I posted. I don't have much choice about where my equipment is anymore, or the other devices connected near it. So I either find a way to mitigate the problem, or just stop using it altogether.

No worries.

Out of curiosity, have you calibrated your scope/probes? Pretty sure mine expects you to clip onto a test point on the scope (Gound and probe) and then you run autoset and if the trace varies from what the manual expects, then you need to adjust the grub screw on your probe until it does match.

Might be worth a try.