evasive wrote on 2020-12-11, 19:03:

I have added both boards to UH19, maybe someone recognizes them and will add info.
http://www.win3x.org/uh19/motherboard/show/6889
http://www.win3x.org/uh19/motherboard/show/6890

You could take the first picture of the board, which does not have red rectangles on some chips. 😀

😦

Done

Unless there are any good ideas to check anything more i'll try to find time during the weekend to unsolder the io controller chip and/or the chip right by it, which go very hot when board is turned on.
IO controller related stuff should not be required parts to make the board work, while it may be the thing preventing it to boot.

So!

After removing the DIP chip on the picture, the io chip and dip above the removed one still went hot. Then i removed the other DIP chip, yet the io chip still went hot. Then i removed the io chip (accidentally slightly melting the dip switches below) and now the board boots!
So i've found the problem and now it's only a matter to find a replacement UM82C862F chip! (If you have one and can't put it into use, maybe we can find a deal here? I have bunch of Goldstar 2c controllers but no UM chip based ones...)

Resoldering such chip can be done easily with soldering iron, right?

Also, one mistake i might have made with kapton tape is that probably you should not let half of the tape flap around in the air, right? The kapton tape itself started melting on the parts where it wasn't attached to anything. (it held nicely on the parts it was attached to the board) Aluminium foil should be used on those flappy parts, right?

EDIT: Found a pinout for UM82C862 (non-F) and checked with multimeter all the VCC and GND pins and it seems to match: https://ia803002.us.archive.org/BookReader/Bo … 453427&rotate=0
Also, under the chip, there's marking of "82C862", which maybe means, there are some chips around without the "UM" prefix that would still suit?

A small update to the whole saga.

With ISA Super IO controller card, the machine works perfectly. I have installed DOS 6.22, Windows for Workgroup 3.11 on it as software and i have ESS ES1869F sound card and 3COM 3C509B network card on it too fully working.

So unless i stumble upon this chip sometime soon, this is how this machine works today. Too sad, that the integrated IO ports don't work and i have only 2 spare ISA slots for additional cards. (Occupied now by NIC and sound card)

Well I guess you could always try to sacrifice a I/O card with that chip to replace it, it's up to you.
Or maybe there are pin compatible chips ? Who knows ?

Deksor wrote on 2021-01-12, 16:03:

Well I guess you could always try to sacrifice a I/O card with that chip to replace it, it's up to you.
Or maybe there are pin compatible chips ? Who knows ?

I wish i had an IO card with that chip. All my io cards are with Prime 2C chips and i have bunch of them... 🙁

I've found the appropriate Super IO card and transplanted the main chip there. The computer now boots while this chip is on the motherboard! (it did not, when the old chip was on the board)
HDD and FDD are working.

There are some driver chips getting very hot and i can't get 2 com ports to appear, but the same superio card contains the same supporting chips as the motherboard has.

It's too late today, but seems like i'm gonna get this motherboard fully working soon!

Good job !

I switched the 2 driver chips and voila - second serial port appeared for the machine and all ports are working!
In total, i replaced the IO controller chip, 2 driver chips (you can recognize them by seeing 2 "Goldstar" chips instead of Motorola chips) and 2x6 switch sets (red), because i accidentally melted them when i removed the IO controller chip. And of course the battery is also brand new Ni-MH type one.

I also documented few switches and am going to try to make sense of them to contribute for the documentation.

I'm gonna set it fully up with 8MB of ram, ~100MB of HDD, SoundBlaster compatible soundcard, 3com NIC and a good assortment of software starting with DOS 6.22, Windows for Workgroups 3.11, Microsoft Entertainment Pack and if there's more room, a Word 6.0. (There's definitely not enough room for full Office 4.3 suite)
... and then, because i already have my own 386 pc to play with, i need to find a good person to give a new home to this computer. 😀

But for now, here's the latest pic of the board in full working condition:

The saga continues, i've found 2 pins of io controller to be shorted and so the floppy drive doesn't properly seek. Couldn't get rid of the short with soldering iron, so it must be deep under the chip. Maybe during the weekend i have the time to completely remove and re-attach the chip once again...

Back in days when i soldered that chip onto the board, i had the worst equipment possible. Now i have a lot more and better tools so shouldn't be a big thing.

I don't even remember how many times i've had to completely disassemble the whole computer - you can not get the motherboard out without completely taking the whole case into pieces...

I feel your pain, I need to fix a really cool multysinc CRT monitor and I think I identified the problem, but so far I haven't been able to find the time and the energy to do it.

This crt is packed with PCBs, wires and metal shielding. The culprit I suspect ? Capacitors.

Oh I've already replaced most of them ...
But the capacitors I suspect are on the PCB that's the deepest in the monitor. To get it, I need to disassemble litteraly everything ...
I've managed to disassemble it once and iirc it took me like 45 mins to be finally able to get it free.

Sadly back then I didn't take the time to read the caps' values 🙁
So I'll need to spend a lot of time to disassemble it, note each cap's value, reassemble it and soon disassemble it again to install the fresh caps.

I don't know if it's a good thing or a bad thing that I discovered that I have specifically good memory in remembering how to put things back together that I took apart months, years, decades ago, so I've got a lot of stuff in parts in boxes waiting for parts to turn up cheap or opportunity to fix or whatever. However, today we have video cameras with ample storage, so you could video how it comes apart, set it all aside until the parts come in.

I'd do this, but I don't have the room and I'm pretty bad at this even with video, I can loose some parts.

Now, it is in full working order! It took quite some time, but it's beautiful in the weird way this machine is. 😀
Re: What retro activity did you get up to today?