Place holder for some Pictures.

More Pics

If you think you've flushed out the vinegar with the alcohol, you should be OK. I usually just rinse the board in water afterward. Thoughts on that vary, but I live in a dry climate with good water quality, so it's pretty easy to dry the board thoroughly, and I don't really need to worry about mineral deposits.

My advice is to check on it regularly. Maybe pop the hood in a week, then a month, then a couple months, then next year. Some people have had issues with corrosion "coming back", if it didn't get cleaned well enough. Be vigilant and catch any relapses before it causes damage. Other than that, just enjoy it. 😀

That's a nice find. As much as well all love to customize and tweak our rigs, there's something special about finding a pristine OG specimen out there in the wild.

Thanks! I will be keeping an eye on it. We shall see.

As for keeping it stock, will just be adding a soundcard, cdrom, maybe a NIC, have not decided on that one and will upgrade the drive with a CF adapter.

Lovely rig, no doubt.

But I don't believe you've flushed all the acid out. Not if you can plainly SEE it in the pics. Something like this needs some localized scrubbing and then neutralization. Also the solder should be reflowed. Traces checked, sanded, coated/replaced, and then sealed again.

The acid migrates over time and continues to spread if not removed. The damage right now looks easily fixable, but in time things that are silver, will turn grey. And that surface acid will eventually make its way into the PCB layers. More work needs to be done. I speak from direct experience on this.

CMOS stuff is rather sensitive and hi-impedance. This means that the slightest trace of acid can generate current when in contact with metals.

I just repaired a board where a drop of acid so small as to be seen only under a microscope at angle was generating power between ground and PWRGOOD and PSRSTB#. Improper voltage levels/signals here cause the RTC in the 82C206 to not cleanly take itself in and out of circuit properly. And to not cleanly reset ether.

So this causes high current draw if the 82C206 stays in-circuit, leaking power to the rest of the mainboard address lines. Or it could corrupt several registers as the system transitions between power-on and power-off. Especially if the signal is in-between what it's supposed to be. The chip and stay half-in and half-out of circuit.

Granted this is specific to my board, but the concept applies to acid and metal and CMOS all exhibiting erratic operation due to stray currents in the uA or less range.

Some circuits are never affected by this because they need mA range current and several volts to trigger. No so with high-impedance CMOS inputs.

I marked the areas that look like remaining acid deposits. And what's under the chip?

If the bright splotches will not come off, they may be on the inside of the board. If a bright piece of the board is nicked with a pin in the suspect area, a bright speck of lamination may crack off, reveling corrosion underneath.

Or the acid may have been concentrated enough to attack from the top, but not making it all the way through. Best case! Seen both conditions.

The topmost surface usually turns green where it broke free of the underlying copper and now reflects light differently. So.. Using specialized tools, a neutralizing agent can be injected and then flushed. Probably not something for the home hobbyist to do, but the first layer of insulation can be removed, the work done, and then re-coated over. Practice on a scrap board.
l
Other experiments I've done include a quick activation and quick dry accelerant. What else do I call it? Brush it on and it kicks the surface acid into conduction and it generates enough voltage and current to flip gates and make your DMM happy. Lasts about a minute. Once pinpointed, repair can then be done.

A friend of mine simply pours on the flux and solder, brush clean, and repeat, till everything is shiny. The claim here is that the high temps speed up years of slow-acting corrosion into mere minutes or seconds. Burn the stuff away, has a sweet cardboard'y smell most of the times. Seems to work well on some sufaces or vias, but will soften the enamel coating on resistors and tantalum capacitors, which then can eventually re-harden. Which is good.. But IMHO they're now compromised and more susceptible to ambient humidity. Replacement of such parts is usually in order.

I suppose it's a matter of examination and experience that says what technique to use where.

Very nice find indeed!
-I'm not sure abut this exact case but rails are hard to find for anything after a few years, Your best bet is to get "creative"
-Cooling wasn't even a consideration when these were built, It's probably not needed but cant hurt mounting a fan to increase air flow or add a heat-sink on hot chips.
- RAM also has different speed measured in ns on the chip 80ns is fine for a 486 with 30 pin ram
- Yes the extra holes are for different CPU's Nothing to worry about.
- You may have to set a jumper to tell the motherboard to use an external battery, after that your good to go.

Thanks for the write up, ok, I will pull the board again and try to clean more, for a n00b like myself trying to clean battery acid from pcb first time ever, what do you suggest I scrub with? What fluid if any should I use?

Keatah wrote:

I marked the areas that look like remaining acid deposits. And what's under the chip? […]
Show full quote

I marked the areas that look like remaining acid deposits. And what's under the chip?

If the bright splotches will not come off, they may be on the inside of the board. If a bright piece of the board is nicked with a pin in the suspect area, a bright speck of lamination may crack off, reveling corrosion underneath.

Or the acid may have been concentrated enough to attack from the top, but not making it all the way through. Best case! Seen both conditions.

The topmost surface usually turns green where it broke free of the underlying copper and now reflects light differently. So.. Using specialized tools, a neutralizing agent can be injected and then flushed. Probably not something for the home hobbyist to do, but the first layer of insulation can be removed, the work done, and then re-coated over. Practice on a scrap board.
l
Other experiments I've done include a quick activation and quick dry accelerant. What else do I call it? Brush it on and it kicks the surface acid into conduction and it generates enough voltage and current to flip gates and make your DMM happy. Lasts about a minute. Once pinpointed, repair can then be done.

A friend of mine simply pours on the flux and solder, brush clean, and repeat, till everything is shiny. The claim here is that the high temps speed up years of slow-acting corrosion into mere minutes or seconds. Burn the stuff away, has a sweet cardboard'y smell most of the times. Seems to work well on some sufaces or vias, but will soften the enamel coating on resistors and tantalum capacitors, which then can eventually re-harden. Which is good.. But IMHO they're now compromised and more susceptible to ambient humidity. Replacement of such parts is usually in order.

I suppose it's a matter of examination and experience that says what technique to use where.

IMG_20190119_203935markup.jpg

chinny22 wrote:

Very nice find indeed! -I'm not sure abut this exact case but rails are hard to find for anything after a few years, Your best b […]
Show full quote

Very nice find indeed!
-I'm not sure abut this exact case but rails are hard to find for anything after a few years, Your best bet is to get "creative"
-Cooling wasn't even a consideration when these were built, It's probably not needed but cant hurt mounting a fan to increase air flow or add a heat-sink on hot chips.
- RAM also has different speed measured in ns on the chip 80ns is fine for a 486 with 30 pin ram
- Yes the extra holes are for different CPU's Nothing to worry about.
- You may have to set a jumper to tell the motherboard to use an external battery, after that your good to go.

Found some rails, they came with a seagate HD originally as a kit to upgrade a PC-AT. They fit perfectly. So it seems it was possible a spec at some point that no one really followed officially.

Holds that modern DVD Burner perfectly 😀 Not that the system could ever burn a dvd!

I ordered some 4x9 60ns simms for this the manual recomends 80ns or faster. BTW I have the original manual for this board if anyone ever wants it.

I did remove the jumper for the onboard battery, that just disconnects it, with the battery gone, does basically the same thing. Installed the external one seems to be holding out!

I did install a DX4100 Overdrive, system is much snappier with some games I tried now, yay to dukenukem 3D! I was able to keep the 128kb L2 cache enabled too, which I heard was a problem for some people.

Also fixed the fan on the PSU, realized after the system got super warm, that it was the PSU overheating 😀

Don't worry system was shut off at the powerstrip before working, this was for ease of testing. Fan was soldered on, so had to butt solder, shrink and shrink again.

Old one span, but needed a kickstart to get it moving, oiling it didnt help (even though all the old oil was gone)

32bitdx wrote:

- The 386 socket is of course empty, but why does the 486 socket the CPU in have extra empty holes in the socket? Is this for Cyrix or other CPUs? Manual is not clear on this.

These combo boards often re-purpose the 486 socket as a socket for 387 FPU when a 386 CPU is present. Then the inner holes are used instead of the outer ones (387 FPUs are much smaller than 486s), which are for the 486 CPU. If they overlap - well, that's funny but these combo sockets do exist.

alvaro84 wrote:

32bitdx wrote:

- The 386 socket is of course empty, but why does the 486 socket the CPU in have extra empty holes in the socket? Is this for Cyrix or other CPUs? Manual is not clear on this.

These combo boards often re-purpose the 486 socket as a socket for 387 FPU when a 386 CPU is present. Then the inner holes are used instead of the outer ones (387 FPUs are much smaller than 486s), which are for the 486 CPU. If they overlap - well, that's funny but these combo sockets do exist.

You are indeed correct, have not had much time to play with the system since I got it up. Will deep dive on the board again in a month or so to clean some more.