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Reviving an unbranded/unknown CPU-3216SX AT motherboard.

GearTechWolf

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Joined
Apr 24, 2015
Messages
264
Location
Washington
This is the board: https://theretroweb.com/motherboards/s/unknown-cpu-3216sx
InfonetPC-1.pngInfonetPC-2.pngInfonetPC-3.png
(funny thing, the latching switch was in the location for the Reset switch and the momentary was in the Turbo-switch spot, from the factory!)
I was checking the old stored computers from my younger days to see if any still had their CMOS batteries in them and this one did, it was even a Varta!
It had leaked, of course, but the damage was surprisingly minimal! Mild green surface-corrosion on a couple 74xx/74xxx-logic chips and a couple ISA slots.
Pulled the keyboard controller to clean it and its socket, even though it wasn't green, and everything cleaned up really nice with just some white vinegar!
Everything came back to clean enough to make good contact except for the socket at U55, holding some kind of PAL chip, which itself cleaned up with mild sanding.
I don't have the greatest setup for de-soldering multi-pin stuff like this DIP-20 socket and wasn't looking forward to futzing about with de-soldering braid.
Then I had an idea, I could cut it free and then pull one pin at a time! Using an old/dull/broken Stanley razor utility blade, I cut the pins between socket and board.
InfonetPC-4.pngInfonetPC-5.pngInfonetPC-6.png
(bent/rusty pin I found in the shed works great to pull out the bad contacts in the socket!)
Worked great! I can even clean and repopulate this socket with new pins/receivers since it's intact and I have a bunch of used pins from sockets where the plastic melted when I salvaged them from junk boards. Sure, sockets don't cost much, but I'm currently working on a zero-cost budget until I get a job again. And it's fun!
If this 386 system works, partly determined by getting a power-supply for it working, I can test my piles of ISA cards!
More to come as I get around to it, and I'll post the hi/lo BIOS dumps when I get those read. (once I find where I put them...)
 

GearTechWolf

Experienced Member
Joined
Apr 24, 2015
Messages
264
Location
Washington
Thanks, @ajacocks ! I was very happy with how well it worked. It cut through the mildly-corroded pins easily and left stumps that pulled through the board without damage. Just have to clear the solder from the holes (probably use some fine-tipped round toothpicks) and I can fit a new socket.
Then I just have to find the danged BIOS chips and the PAL chip that goes in this socket! I've misplaced them. Then I'll be close to testing!
 

GearTechWolf

Experienced Member
Joined
Apr 24, 2015
Messages
264
Location
Washington
Well, as I said in my other thread on the power-supply for this computer, the power-supply doesn't have a fault!
I just wasn't providing it the load it needed to start-up. Sadly, I didn't realize this prior to cutting off the P8/P9 connectors to build an ATX-to-AT adaptor.
So I'll have to undo/fix that as well as finish the mobo repair before I can finally test this thing.
However, I did at least find where I'd put the BIOS chips! So I dumped those and the files will be available in my BIOS-dumps thread.
Also got the case/bezel washed up, scraped out most of the rust hiding under damaged paint, and got it as clean as it needs to be.
So I'll be able to slap it all back together once everything is fixed. Then I'll find out if all this effort was worth it or not! Hopefully it was.
 

GearTechWolf

Experienced Member
Joined
Apr 24, 2015
Messages
264
Location
Washington
Okay, got the connectors reattached to the power-supply, got the socket replaced, and got the mobo and the power-supply put back in the case.
Hooked up the speaker and did a smoke-test, it works! Haven't tested with any cards, a keyboard, or a screen yet, but it gave beep-codes!
Eight short beeps, a pause, and a single beep. Which, according to this page: https://www.computerhope.com/beep.htm is a video memory read/write error and that makes sense as there was no video card installed. One beep is a DRAM refresh failure. Odd that would have an error after the video memory was tested. Further testing will have to be done. But hey, the mainboard seems to work fine so far!
 

GearTechWolf

Experienced Member
Joined
Apr 24, 2015
Messages
264
Location
Washington
Tested all of the ISA video-cards and floppy-controllers/multi-IO cards I had immediately on-hand, then later tested all the 3-1/2 floppy drives I could find.
Most of them worked! Only a couple VGA cards and a several floppy-drives refused to work fully, or at all.
Was going to use ImageDisk to run diagnotics on the flaky floppies but ran into an aggravating issue.
Running the cleaning-disk through my USB 3-1/2 floppy drive knocked it out of alignment and now I can't make disks with it!
At least, not ones that the 386 will read, or vice-versa. The USB-floppy can only read disks formatted by itself now, and no other drives can read those disks.
So until I replace it or find a workaround (maybe setting up an XP-box with a floppy-drive and USB ports for flash-drives), I'm stuck.
USB floppy-drives sure are fragile, ain't they? I got this one for $3 at a thrift-store, but it originally cost $50-ish!
 

GearTechWolf

Experienced Member
Joined
Apr 24, 2015
Messages
264
Location
Washington
They really don't hold up all that well, do they? If they weren't made to run off of USB power they could be made more sturdy.
Sure, they'd be heavier and require a separate power-supply, but I'd be fine with that!
I don't care about the portability, I just want to connect a floppy to a modern computer!
 
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