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astamp
July 1st, 2017, 11:20 AM
Hello,

I recently picked up an AT clone that doesn't POST and was looking for advice on how to get it going.
After removing all of the option cards and drives and reseating the power cables I was able to get it to start up and beep 5 times (maybe 2-1-2 but I may be hearing things).

After scanning the motherboard I saw what looked to be a chipped ceramic capacitor so I pulled out the board to find a ton of corrosion under the power supply.
(The capacitor looks like it just had a clear top?, there are more than one on the board like this so it may be ok.)

The motherboard is an ATEGA-800 with an 8 MHz 286. The ROM chips read G2DS00 Rev. B (C) 1991 Micro Firmware. One had the erase window showing so I covered it up with some tape.

Has anyone worked with this motherboard before and know what the 5 beeps represent?
Also how do I clean up the corrosion without damaging the motherboard/components? There was an external battery pack (4xAA cells) attached to J33 so I'm not sure if I need to repopulate that battery if I clip it.

Thanks,
--Andy

3943539436

mR_Slug
July 7th, 2017, 02:07 PM
You may be able to find out what the beep code is by looking it up. Here is a good reference:
http://www.hp64000.net/scansioni/Pc_Engineers/Pc_Engineers_Vol1dl-BIOS_Companion.pdf

However I have never heard of the company Micro Firmware. It may be an updated BIOS, as that board looks like a design from way before '91. It may also follow the beep codes from AMI or Phoenix. If you remove the on-board battery you will need to add an external one to retain BIOS settings, but it should not require one in order to boot.

That corrosion is very bad. Careful scraping and vinegar can be used to remove and neutralize the corrosion. There are lots of guides on the internet. The corrosion is bad enough that I think your likely to have many broken traces. Assuming that those pin headers in the second picture are for serial and parallel, you may be able to leave this part of the motherboard broken. Those large chips behind them may be more important. What are your soldering skills like?

Generally for whatever corrosion you can see, there is at least 1/2 as much again. I would at least try re-seating the RAM, but to be honest I think you're going to have an uphill struggle with this one.

Stone
July 7th, 2017, 02:22 PM
... But to be honest i think you're going to have an uphill struggle with this one.ditto...

Chuck(G)
July 7th, 2017, 02:33 PM
Yes, it looks bad around the serial port headers, but maybe you don't need them. Get some plain white vinegar, clip the battery out and give the area a good scrub with vinegar and a soft toothbrush and see how much of the green crud you can remove. Rinse thoroughly with water.

Then take some more photos see what you've got. That the thing let out a string of beeps is (relatively speaking) good news.

T-R-A
July 7th, 2017, 04:44 PM
I clean up stuff as bad or worse every day at work. Isopropanol, a stiff brass toothbrush and tacky-flux with low-temp solder and solder wick---assuming your soldering skills are pretty decent and you don't hit the board too heavily with the brush. Clean as much as you can with the Isopropanol then whisk somewhat gently with the brush. Clean again with the Isopropanol. Use tacky-flux and low-temp solder to "re-tin" the pads. Wick-off with solder wick. Inspect with a good ring-light or microscope to make sure no pads are missing/traces broken.

T-R-A
July 7th, 2017, 04:48 PM
Should have added:

Tacky-flux:
https://www.digikey.com/products/en?mpart=SMD291&v=315

Low-temp Solder:
https://www.digikey.com/product-detail/en/chip-quik-inc/SMDSWLTLFP32/SMDSWLTLFP32-ND/5180411

Other items should be available locally.