You can always swap the RTC from a working board to verify the old RTC is the cause of this error.
We don´t know what - corrupt - data is stored in CMOS right now and resetting isn´t possible.

I have to add to my previous statement.

While the BIOS stays inaccessible, the system is still somewhat functioning.
I'm able to reset the board by pressing the reset switch.
It also detects when no keyboard is attached.

Unfortunately, I can't verify if the RTC causes the problem, since it's the only one I have right now.

However, I could try something else.
My first idea would be to attach a CR2032 to the RTC module.
The second idea would be to flash the BIOS chip, using my GALEP-4 programmer.
I was able to find a ROM on theretroweb.com.
But before I do any of that, I want to make sure that I'm not missing anything.
Maybe someone else had a similar issue before and knows how to solve it.
Perhaps the best thing to do would be to find a replacement for the DS12887A chip.

What do you think?

To avoid confusion: When I said earlier that the RTC is dead, I was referring to its built-in battery.

Do the "Dallas-MOD" with a CR2032. Make sure to disconnect one of the connectors of the old battery while dremeling.
You have to enlarge the opening at one of the contacts up to the top of the RTC housing (and a little deeper) until you see the wire that leads to the old battery. Cut it right there - not at the bottom of the housing where the DIL pins are!
By doing so you reset CMOS before the new battery is connected.
You also prevent the new battery from being slowly discharged by the old one.

Okay, I'm going to try this.
It shouldn't be too difficult.
Please bear with me, this may take some time.
I'll get in touch with you once I'm done.

There are lots of tutorials online...
Good luck!

Today, I successfully modified the RTC.
Unfortunately, the same problem persists.
At least, it no longer reports a dead system battery.
Judging by the fact that no keystroke gets detected, I assume that the keyboard controller might have died, but I can't confirm that.
My keyboard definitely works.
I could try to reseat every socketed IC and give the board a good clean.
What do you think about that?
Tomorrow, I'll also check the jumper settings. Maybe some jumpers are set incorrectly.

There is a small fuse next to the keyboard connector, right in the corner of the PCB. It looks like a green or yellow resistor and is marked as "F1" on the PCB. Maybe it has blown, this would prevent the keyboard from getting any power. You might want to check that fuse for continuity.

The fuse was fine. I checked it earlier.
It's odd that the board detects when no keyboard is attached.
However, as soon as I plug in a keyboard, it does nothing.
I don't think the board locks up, instead it seems that the keyboard won't get initialized at all.
I also checked the jumpers, and they seemed to be set in the correct positions.
This is far beyond my understanding. I don't know what to do anymore.

Surely you don't have the keylock (J14) locked? No jumpers on it in any position?

There's no jumper on j14. That was the first thing I checked.

ECS implemented quite an unelegant design here.

Besides the "CMD" PCI IDE controller there´s a SMC "FDC37C665GT ", a super I/O with FDC, (ISA-) IDE, LPT and 2x COM ports.

Then there´s a UMC "UM82C865F", another super I/O (I can´t find a datasheet of this chip). I think it can provide 2 x COM, LPT and gameport - but no FDC.
All this (except gameport) could be done by the SMC chip that already provides a FDC - so why did they add it? Does it have a KBC?

The alternative would be the KBC is in the peripheral-chip = UMC "UM8886F". But I can´t find a datasheet for that also.

Just take a closer look where the traces from the keyboard connector go. On the photos I found they *seem* to go to the UM82C865F.

While at it you should carefully test all solderings at the mentioned chips (except the CMD) for secure contacts. You can tick each pin with a pointy toothpick from the side applying a little force to make sure there are no loosened pins!
And a high-res photo of this area of your board would be useful.

https://theretroweb.com/motherboards/s/ecs-um … 10p-aio-rev-2.x ?

does the keyboard flash its leds when resetting computer?
does pressing capslock light up the led?

majestyk, there's an IC near the CPU, labeled "AMIKEY-2". 
Could this be the keyboard controller?
Also, I will check the contacts of the mentioned IC and take some photos of the area.

rasz_pl, the keyboard doesn't flash its LEDs when resetting the computer.
It also doesn't light up when trying to press the caps lock, scroll lock and num lock key.
It only flashes briefly when I turn on the computer.

Wilius wrote on 2022-09-14, 12:53:

majestyk, there's an IC near the CPU, labeled "AMIKEY-2". 
Could this be the keyboard controller?

It definitely is.
What revision is your UM8810PAIO? Probably 1.x...

You guessed it right. It's revision 1.1

Is the Amikey KBC soldered or sitting in a socket?

If it´s in a socket (as it should be) you can replace it easily. Keyboard controllers fail quite often.

Luckily, the IC is in a socket.
I do have a broken ASUS p/i-p6np5 in my hodgepodge.
It has the same AMIKEY-2 KBC.
Do you think I can simply swap it over?

Just in case anyone is wondering why I'm sacrificing a socket 8 board, it's because it suffered severe damage during shipping.
Trust me. It's beyond fixable, I tried.

You can simply swap the KBCs.
And you´re not sacrificing the nice Socket 8 board - just borrowing a KBC from it 😉

I can confirm that the KBC is not the problem.
While I was at it, I also checked some of the other components.
The following components are working.
- CPU
- RAM
- L2 Cache
- GPU
- RTC
- KBC
At this point, it can only be a faulty component, or the BIOS is corrupted.
I could try flashing the BIOS with my GALEP-4, but never used it before.
Can someone please explain to me how to use this tool?
I also noticed this board has some electrolytic capacitors.
Should I try to recap this board before I'm tinkering around with the BIOS chip?
At this point, I'm also uncertain if the jumpers are set correctly.
Can someone provide me with the jumper settings for the A80486DX4-100NV8T?
I have already tried setting it up for the DX4.
I followed the instructions on this website: https://stason.org/TULARC/pc/motherboards/E/E … M8810P-AIO.html