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286 motherboard ident and troubleshooting

nixxon

Member
Joined
Jul 2, 2007
Messages
11
Location
Bucharest, Romania
Hello everyone,
I bought a lot of three boards especially for this one, as I have a soft spot for TACT chipsets, but so far it didn't prove a lucky buy - in what is my worst percentage so far, only one of the boards works (a KouWell-330 with an i386SX).
Here is a picture that will save me typing 1000 words:

TACT board.jpg

Seems to be made by Vtech (their logo is on the KBC chip, also the labels on KBC and BIOS say "VIDEO TECHNOLOGY INFO-TECH LTD.", but I couldn't find it on th99/stason or any other place.
The only other marking is a label on the first ISA slot, it says "L286-3 CIJC"
It came fully populated with 44256 and 41256 RAMs, around three megabytes I think. But as the board didn't pass initial testing (hang at code 16 on POST card), I removed all the chips and only populated bank 0 with known good chips. That didn't solve the problem, but at least I noticed that it beeps and stops with code 10 when no RAM is present.
It had some corrosion around the battery, not great, not terrible, so I proceeded to clean it as best as I could, removing parts to make my job easier. Found two traces eaten away, so I restored them with thin copper wire, checked every trace and via in the area and there were no other problems so I was quite sure the board is fixed. But after fitting back the parts it hung again, same code 16!

I started playing with the DIP switches, and after a few tries found some combinations that let the board move further during POST. Now it hangs with code 19 with a VGA card installed, or goes to 1A without a card.
The switch settings are "documented" on the board, but frankly it seems like gibberish to me. Here's a detail of the area:

TACT switches.jpg

There isn't a datasheet for this chipset, or at least I haven't been able to find one; maybe a datasheet would provide some info about what MEMSS, IOCHSS mean (and how they should be set up).
Apart from those switches, there are quite a few jumpers on the board, and so far I could only identify two of them. IB/EB near the external battery header toggles between internal and external battery, and 128/256 near the BIOS chips, well, to choose their type. Also there is a small switch labeled SW1 right next to the keyboard connector.

Another quirk of this board - it doesn't seem to have a Reset header (or it isn't working). Of the three white headers (lower left corner in photo), one is for speaker connection, and I've tried shorting the others in every combination, board doesn't reset.

So this is it, shortened the story as much as I could, I'm stuck now so every suggestion/idea is welcome.
Here are some more (full-res) pictures of the board:

https://imgur.com/a/YdNh1Ug
 
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