Wow nice find. Someone just threw out a treasure. Looks like the battery leak is limited to itself and the board is not affected. Have you tried powering it up with a video card?

Thanks I thought so too! To be honest I didn't know that there's this much interest in 486's again. But when I saw it laying there with the Turbo button I had to take it home.
Unfortunately I have almost no old hardware anymore so no spare ISA video cards. First I want to clean everything up and check if the PSU's voltages are okay. This thing probably hasn't been powered on in 10+ years so I want to be careful.

I did buy an ISA video card on eBay, a Cirrus Logic GD-5428 with 1MB which is supposed to be quite good. I'll have to wait for it to arrive which gives me some time to clean up the rest and get a PS/2 to DIN adapter cable 😀

Remove that battery ASAP. Connect an external battery. Clean corrosion off motherboard with some Vinegar and water and scrub with a small brush like a tooth brush and clean with a Q-tip. Rinse with water.

I'm making an attempt at identifying the board (it's about all I can do with this weather)

There was (or even is) a manufacturer called "P&Q" that made 486 motherboards. They had a "L-9620-8" that looks quite similar, except that it also had VLB.

But I can't find much about these motherboards yet. Maybe they didn't sell them under their own name.

[edit]
I went through the 486 boards at Stason.org and I didn't find it. It's possible of course that I missed it. This one came closest I thought.

Yeah it's a good idea to make sure the PSU is OK. Once that checks out you can hook up a speaker and power up to see if it beeps.

With a BIOS dump or a POST screen photo it should be easier to id this board.

I don't think this board is on MTL/Total Hardware 1999 at all. The board @HandOfFate has found is actually a pcchips board.

Yes, and I'm also not sure it was manufactured by this P&Q company. P&Q did make things with UMC chipsets as well so if this M-423 came from P&Q, maybe "Ilon Usa inc." also sold their UMC chipset boards?

But otherwise it's very close, it even has that white tie wrap around the oscillator: https://f.aukro.cz/images/sk6956116747/0558d8 … ae-ab9b63a27496

I wonder what this was used for. I think the 486DX-50 was a fancy high end chip ideally suited for an ISA-only board like this since there are no VLB issues. An ISA-only system would be good for anything CPU-intensive but video and disk I/O will be hampered.
20ns cache chips are on the slow side for 50MHz, no? I wonder if the BIOS will default to the right number of wait states or if you will have to set some.

It looks like you have 6 RAM SIMMs, which is weird. Perhaps 2 got "borrowed" like the video card did. Those 30-pin slots either need to be half-full or entirely full on this machine. If you get the "bug" like many on here and start maxing this thing out, be aware that there can be issues with putting 16MB or more RAM in an SVGA ISA-only system (due to there being no room for the linear video frame-buffer) so don't go crazy with RAM. I'd stick with 4 or 8 MB, which would have likely been the two options offered when this system was bought new, those sizes in 1993 corresponding to about 8GB and 16GB today in terms of fanciness.

Back in the dialup days, finding this machine in a dumpster like that would have made a nice Linux system to share a home dialup connection among multiple machines 😁

I can see this being used for business/accounting purposes back about 1992-93 where the cpu and ram were important. That would be about same time VLB was just being released so figures no VLB, my earliest VLB board is from mid 1994. Just rambling...

I've taken this from a dumpster at work. I work in IT and we put old hardware that returned from customers in there for recycling. So I check it regularly for interesting hardware. This is the first time I've found something this old in there. This is the picture a colleague sent me that triggered me to check it out:

I took the Compaq Deskpro 2000 (Pentium 133, 48MB EDO RAM, 1.6GB HDD) as well. It's working fine after replacing the permanent coin cell with a coin cell holder and a new CR2032. The hard drive still works and has the Compaq diagnostic partition on there as well as a Windows 95 installation. Seems it was last used in around 1999. Last but not least I took the Dell Optiplex GX1 with a Pentium II. It has onboard video and sound but also a PCI video card and an Aureal Vortex sound card in there. I'll check that thing out later.

Back to the 486, so yes it must have definitely been used as an office computer. There were 8 SIMs in there, on that one picture I had taken two of them out to identify. There's 4x Hyundai 1MB and 4x Samsung 1MB so I guess the machine originally came with 4MB and was later upgrade to 8MB. I've cleaned up the battery residue and it came out quite nice. I still have to put some lacquer over the exposed traces.

The motherboard has an external battery pin header. There was a jumper over pins 2 and 3 which (I assume) connected the onboard battery to the RTC. I've removed that jumper, now it's just a matter of connecting a battery pack to pins 1 and 4? Can someone recommend a battery solution? I've seen a blog were someone wired up a coin cell holder to an internal speaker cable and that worked fine. But 3V is quite low?

Then I cleaned the rest of the board, should be ready to go:

To be continued!

I've cleaned the tower and the PSU. The PSU's voltages are not great but I guess it should work: 5.1V, -4,2V, 11.3V and -10.8V. The PSU is from 1997 so it's a replacement unit.
Ready to test:

I've powered it on and... Beep codes! 8 to be precise, which means: 8 short - Display memory read/write error - The system video adapter is missing or defective.
Looking good! Will have to wait for the video card to arrive 😀

Theodinator wrote on 2020-08-16, 11:48:

I've cleaned the tower and the PSU. The PSU's voltages are not great but I guess it should work: 5.1V, -4,2V, 11.3V and -10.8V. The PSU is from 1997 so it's a replacement unit.

Is that without any significant load? It looks like 5V is high and all other voltages are low. AT supplies usually have a single regulation loop for all of the voltages, with focus on keeping 5V in spec. If the load on 5V is way lower than expected (having a mainboard, a processor, a graphics card and a hard drive connected is expected), 5V might be so much too high that the control loop turns back the supply that all the other voltages get low. I don't think this necissarily indicates problems with the supply in the current state of the computer.

Theodinator wrote on 2020-08-16, 11:43:

I've taken this from a dumpster at work. I work in IT and we put old hardware that returned from customers in there for recyclin […]
Show full quote

I've taken this from a dumpster at work. I work in IT and we put old hardware that returned from customers in there for recycling. So I check it regularly for interesting hardware. This is the first time I've found something this old in there. This is the picture a colleague sent me that triggered me to check it out:
f47fce1a-dfc5-4a26-ba27-47bd59684f0e.jpg
cf26c180-b8bc-41bf-80a7-888c7c69939d.jpg

I took the Compaq Deskpro 2000 (Pentium 133, 48MB EDO RAM, 1.6GB HDD) as well. It's working fine after replacing the permanent coin cell with a coin cell holder and a new CR2032. The hard drive still works and has the Compaq diagnostic partition on there as well as a Windows 95 installation. Seems it was last used in around 1999. Last but not least I took the Dell Optiplex GX1 with a Pentium II. It has onboard video and sound but also a PCI video card and an Aureal Vortex sound card in there. I'll check that thing out later.

That case underneath the dell looks interesting too and well preserved, I wonder what was inside

mkarcher wrote on 2020-08-16, 12:12:

Theodinator wrote on 2020-08-16, 11:48:

I've cleaned the tower and the PSU. The PSU's voltages are not great but I guess it should work: 5.1V, -4,2V, 11.3V and -10.8V. The PSU is from 1997 so it's a replacement unit.

Is that without any significant load? It looks like 5V is high and all other voltages are low. AT supplies usually have a single regulation loop for all of the voltages, with focus on keeping 5V in spec. If the load on 5V is way lower than expected (having a mainboard, a processor, a graphics card and a hard drive connected is expected), 5V might be so much too high that the control loop turns back the supply that all the other voltages get low. I don't think this necissarily indicates problems with the supply in the current state of the computer.

I measured it without anything connected so that makes sense! I just wanted to make sure no voltages were way above spec and it seems fine.

Deksor wrote on 2020-08-16, 12:27:

Theodinator wrote on 2020-08-16, 11:43:

I've taken this from a dumpster at work. I work in IT and we put old hardware that returned from customers in there for recyclin […]
Show full quote

I've taken this from a dumpster at work. I work in IT and we put old hardware that returned from customers in there for recycling. So I check it regularly for interesting hardware. This is the first time I've found something this old in there. This is the picture a colleague sent me that triggered me to check it out:
f47fce1a-dfc5-4a26-ba27-47bd59684f0e.jpg
cf26c180-b8bc-41bf-80a7-888c7c69939d.jpg

I took the Compaq Deskpro 2000 (Pentium 133, 48MB EDO RAM, 1.6GB HDD) as well. It's working fine after replacing the permanent coin cell with a coin cell holder and a new CR2032. The hard drive still works and has the Compaq diagnostic partition on there as well as a Windows 95 installation. Seems it was last used in around 1999. Last but not least I took the Dell Optiplex GX1 with a Pentium II. It has onboard video and sound but also a PCI video card and an Aureal Vortex sound card in there. I'll check that thing out later.

That case underneath the dell looks interesting too and well preserved, I wonder what was inside

I did check it out briefly as the side cover was off. There's a Celeron badge on the front, it has a slot processor in it and two sticks of SDRAM. All cards were taken out so I decided to leave it.

PSU voltages are almost irrelevant when you deal with 20-30 years old hardware.
Just this week my test PSU started to smoke even though voltages were perfect (+12,03V, +5,08V). One of the filter caps died and I don't usually replace those.
It just didn't like a 30W monochrome monitor hooked up to it.
I tend to agree with those who refuse to use old PSUs and use modern, quality ATX types with a converter instead.

Theodinator wrote on 2020-08-16, 11:43:

The motherboard has an external battery pin header. There was a jumper over pins 2 and 3 which (I assume) connected the onboard battery to the RTC. I've removed that jumper, now it's just a matter of connecting a battery pack to pins 1 and 4? Can someone recommend a battery solution? I've seen a blog were someone wired up a coin cell holder to an internal speaker cable and that worked fine. But 3V is quite low?

My board has a separate jumper to select onboard vs. external battery, as well as the four-pin connector like you show here. One of the four pins is missing so that an appropriate battery holder will only connect the correct way. Apparently this was a common configuration as there is a premade 3xAA battery holder #BH3AA-211 you can buy that comes ready to connect. It even comes with velcro to stick in in the case somewhere.

You would have to use a multimeter to trace the outside pins of that ext batt connector and see where they go. You also have to be careful about making sure the board doesn't try to charge any battery you connect. Hopefully removing the jumper takes care of that. In a perfect world, the outer pins would be used for an external battery and you could clip off the correct inner key pin (never to use a NiCd battery again) and use the battery holder I mentioned to connect to the outer two pins.

Miphee wrote on 2020-08-16, 13:07:

PSU voltages are almost irrelevant when you deal with 20-30 years old hardware.

Not exactly. You definitely don't want to over-volt any PC components (if said PSU happens to be out of spec), I've had this happen to a few WD hard drives (they died).

Since then, I'm always checking the voltages on any PSUs that I get.

Today the video card came in and I got the computer to POST!

The computer doesn't seem quite stable however. If I plug in the power cord and flip the switch, it posts. But if I power it off, wait 10 seconds and flip the switch again it doesn't post anymore. After leaving the power cord out for about a minute and trying again it posts again. Bad PSU maybe?