darry wrote on 2021-01-27, 02:25:
This may be relevant to the PS/2 port problem .
P3B-F PS/2 ports stopped working
Yeah, so I did some voltage testing this morning. So in testing the voltages on both ports I was initially getting voltages jumping all over the place, from millivolts to around 2-3V. While testing the voltages, I kind of manipulated the ports, pushing on them, pulling on them, etc. and eventually I started getting a stable 4.9V on the power pins and 5.02 (about) on the clock and data pins. So then I powered down the system again and tried plugging in the keyboard and once again it failed in PS/2. I turned off the system and powered back on checking voltages and found near 0V again.
So obviously something has gone haywire in that section of the board (or even with the ports themselves). In doing some searches based on the link you provided, it seems some people have had issues with other boards with a C151 cap pack (looking at badcaps.net, here at Vogons, etc.). Here's a link to a post containing an image of a motherboard containing such a pack that I found (something PARKE posted): Re: PS/2 ports (mouse and keyboard) stopped working.
Anyway, mine looks like this:
I'm guessing the 4 surface mount items are a discrete cap version of the C151 pack. Interestingly, if you look at the USB port stack immediately above the PS/2 port stack in my image, it looks like those surface mount caps were removed. So I'm wondering if doing the same here might help. I've got a new (much better) soldering iron coming tomorrow that I could use to take a crack at this and probably try resoldering the port stack.
I'm a bit hesitant, though, to just ditch the caps entirely. Based on what I'm reading for the USB ports, apparently they put 47pF NPO caps across the data lines and ground to filter out RF interference. My hunch is that the same sort of thing (different, perhaps higher, values in all likelihood, though) is highly recommended here for the data and clock lines for the PS/2 ports.
EDIT: Fixing image link.
