Tiido wrote on 2024-03-07, 01:57:

Bottommost one should have best performance, with worse in higher slots but the difference is probably small if visible at all. How does direct connection to mobo compare ?

Yeah, I also figured out that what I should do...but at this stage I definitely can't bother taking it all out again. 🤣
No way to test without removing the motherboard from the case with the horizontal back slots. I'll eventually get to it at some point...

kingcake wrote on 2024-03-07, 02:09:

What's the VGA card being used? I've encountered lots of them that were missing +5V bypass caps from the factory.

I tested an ET4000AX and a CL GD5426. Results are pretty much identical.

But honestly, trying again today after a day of work, it's so much better than before the caps that it almost feels like nitpicking at this stage. It's not *perfect* but more than good enough. Doesn't mean I'm not happy to read more ideas, of course 😀

Boohyaka wrote on 2024-03-07, 20:17:

But honestly, trying again today after a day of work, it's so much better than before the caps that it almost feels like nitpicking at this stage. It's not *perfect* but more than good enough. Doesn't mean I'm not happy to read more ideas, of course 😀

I recall something about adding a small ceramic capacitor in parallel to the electrolytics to battle against the higher frequency noise/interference.
worth a try or line of inquiry.

weedeewee wrote on 2024-03-07, 20:33:

Boohyaka wrote on 2024-03-07, 20:17:

But honestly, trying again today after a day of work, it's so much better than before the caps that it almost feels like nitpicking at this stage. It's not *perfect* but more than good enough. Doesn't mean I'm not happy to read more ideas, of course 😀

I recall something about adding a small ceramic capacitor in parallel to the electrolytics to battle against the higher frequency noise/interference.
worth a try or line of inquiry.

This can certainly help. 100nF would be appropriate for medium frequency noise. Sometimes, on very noisy backplanes, I put a 100nF ceramic directly across the +5V and GND pins of the ISA socket solder joints for each ISA slot.

Make sure to keep the leads of the ceramic as short as possible to reduce ESL, which will kill the ability to filter at med freq.

Some of this noise could just be radiated from poor PCB design. Which was common back in the day.