At last I've sort-of managed to troubleshoot something using my oscilloscope. I posted a picture of this board the other day with the front and back traces overlaid - I got this board a couple of years back as someone else had attempted to repair it and not got it working. I couldn't do much better although I did repair a bunch of the vias it still wouldn't do anything.
This is a WTC POP-3254 and the example shown on the retroweb appears to be in a worse state than my one. It's a rather old and basic 386dx board with no cache and the battery had destroyed some traces and vias by the 82c206 chip. It was coming out of reset and the clocks were working, but it didn't do anything.
Checking with the scope on the BIOS EEPROM I could see that there were signals on both the address and data lines, but some of the address lines seemed to have the same signal patterns and went from 5v to 2.5v which didn't seem right, most signals went to a lower voltage for a low signal.
Washed it up in the sink because this board has clearly been exposed to the elements and there were some white marks around most of the pins where I think the lead was leeching out. It cleaned up nicely but that didn't fix anything.
One of the 74LS373 chips had been replaced and socketed by the previous owner so I decided to pull everything in that area off, test it and check the connections of the traces, including the 82C206:
The pads/legs of the 82C206 were a bit corroded so that had to be checked too - there were bad VIAs hiding underneath it. Laboriously tracing and checking each trace that the 74LS373s attached to. The 74LS373 that wasn't replaced was bad after all, but its traces were in better shape.
A front and back picture lets me trace all the lines in Krita and see all the points they pop up - this is doable because this is a comparatively simple 4 layer board with VCC and GND on the inner layers, with signal routing on the outer layers only.
You can see how it looks for tracing here: Re: What retro activity did you get up to today?
This has the underside as the bottom layer with a filter mask layer to adjust the tint. The topside layer goes above that with the Blending Mode set to Lighten - which gives a really nice kind of overlay and the layers are different colours so it's easy to tell what I'm following. Some more layers on top with the set of pins I'm tracing. I'll definitely use this method again in future, I was able to find a bunch of broken connections by following the traces on the screen.
Then drawing a marking by the pin so I can tell it's been checked - only one wire had to be run on the outside, that's the one marked X.
Put it back together and put the 82C206 back on, it powered right up! Yay 😀
For some reason it has a 33MHz Intel 386, but the clock crystal is 50MHz for 25MHz CPU speed. The BIOS doesn't appear to be online and it came to me with no sticker on the EEPROM window, there was a big gap in the ROM file so I was worried the ROM was damaged, but it's fine after all. It's an AMI BIOS with a BIOS string of EOX3-6069-083090-KM
This thing is old enough that it has bios settings configured either with easy OPTI setup which has few options like wait state, or advanced OPTI setup where settings are configured by changing register bits, it's guided but it shows which bits are being altered for 11H, 14H etc. The board's from mid 1991 going by the chip markings but the BIOS and design both say '90, so it's probably the oldest computer I've got along with the Tandon motherboard.
edit: ergh okay so it's not working entirely. Stuff like keyboard works and I can change settings / save settings in the BIOS, but the computer can't boot from a floppy disk. Could that be a problem with DMA? That's handled by the 82C206 and there's a cluster of damaged traces there that were repaired.
It just says insert BOOT diskette and I've tried two known good drives, it does the track seek on boot so I think it's solely down to being unable to read the data.