Some traces are busted around battery area, that's for sure, even ISA slot corroded.

I've checked the corroded traces, non of them are faulty (although far from pretty). That's the first thing I checked when I noticed that corrosion.

Remove the BIOS chip and check for corrosion. You might also want to desolder the DIP socket for the BIOS and check for corrosion. Often, there is quite a bit of hidden corrosion around there when it is this close to the battery.

The proper approach to dealing with busted traces is to use a multimeter on the continuity setting to check for them. Find a trace that looks busted, test it, and if it's broken, try to solder a wire from one point to another.

Since these are multi layer boards, you might have to get a bit more creative with it. If you can find a wiring diagram, you can test everything. I ordered a Mach64 from Ebay which had looked like it was dragged across the road behind a car, but all I had to do was identify one busted trace, put a wire across it, and boom.

it exploded!

http://imgur.com/gallery/E0x4J/comment/1070463503

Yea, under the bios there is a lot of corrosion...

that doesn't look all that bad at all, to me. I'm surprised it's not working.

Ampera wrote:

The proper approach to dealing with busted traces is to use a multimeter on the continuity setting to check for them. Find a trace that looks busted, test it, and if it's broken, try to solder a wire from one point to another.

Since these are multi layer boards, you might have to get a bit more creative with it. If you can find a wiring diagram, you can test everything. I ordered a Mach64 from Ebay which had looked like it was dragged across the road behind a car, but all I had to do was identify one busted trace, put a wire across it, and boom.

That was what I was thinking, have now checked all traces I can see and 1 was busted but fixing that one didn't change anything.

And as Feipoa suggested, I desoldered the socket to see if there was much corrosion but non that I could find (was possibly already removed by the vinegar at that point), and put in a new socket.

To me it seems either the SN74F138N is busted or some traces that I can't see are...

Sorry for the double posting, got another motherboard from the same seller as a replacement from the 4DVS one, the new one being a PAT48PG4 (VER. 1.2A). It seems to have the exact same issues...
I also bought a diagnostics ISA card from ebay (those super cheap ones) and that doesn't give any sort of error code (just:"----") and no activity light what so ever on the "irdy" LED, as with the 4DVS (but blinks like crazy on my working socket 2 board and shows the code while the computer runs fine).

Now I was thinking it maybe is the power supply, but according to the card it should be fine but measuring it myself the -12V line might be a bit weak as it's -10V. However it does power my socket 2 board fine. Considering I can't test my CPU (am486DX4-100) on my socket 2 board nor can I test my 486DX-40 on my newer boards (unless that's compatible with intels 486DX), could it possibly be my CPU?

Any ideas on what I can try?

Is the CPU getting hot after some minutes? Double checked the jumper settings for CPU configuration?

On the Zida, yes. But not on the new board, just keeps cold.

Jumpers on both boards are fine, triple checked. Although I don't understand the DRAM settings here http://stason.org/TULARC/pc/motherboards/T/TM … 4-VER-1-2A.html (but considering the seller used the ram I have here to test it and has the setting in the same location I assume it's fine)

What I might be able to do is check if the board works with the dx40, but I'd need someone that can tell me if I can actually use it on that board considering it's listing doesn't say anything about an AM486DX, just AM486DX4 and AMD enhanced.

Edit:
For some reason I now get error codes on the 4DVS when using the dx40, specifically FD and on rare occasions F9. F9 doesn't exist, according to the little manual. FD means "next programming the flash rom", which doesn't seem to help me with repairing it as far as I can see.

Also clarity edit.

Edit2:
1 motherboard is still non funtioning, (the one that gives F9 or FD). The other works. Apparently the CPU was faulty...

Update, Zida board still isn't funtioning. But think I've got a breakthrough on the second.
I started noticing that literally every 3.3V CPU didn't work and didn't become warm. Which got me thinking, maybe it doesn't get the right voltage (and at this point I was praying it wasn't always 5V and near fried the CPU's). So I got my trusty multimeter and checked pin A16 as that should be a power line to the CPU socket. 1.39V, Which explains why the CPU's don't get warm or function as their simply massively undervolted.

So looking for a voltage regulator that isn't the 5V one I noticed that someone removed the old 3.3V regulator and it's heatsink. (also afterwards I noticed online that the 1 picture that isn't my board has a heatsink there)

So my question now, what part can I put in it's place? The spot is marked R-O-I (next to it they have the exact same but reversed), I being a 5V input, O being output and I a 1V line of some sort.

Edit:Now works, with a LT1086CT