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Is that 486 motherboard dead?

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First post, by Fox_McCloud45

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Hello.

I have recovered an old 486 machine with a traditional 5-pin DIN connector.

I originally purchased a PS/2 to DIN adapter but it turned out none of the keyboards worked. The BIOS successfully POSTs, but I get the following two warnings:

Keyboard error or no keyboard present
CMOS checksum error - Defaults loaded

The CMOS error is obviously caused by the dead battery.
However, the Keyboard Error is weird. The keyboards' LEDs blink when the computer starts, but nothing else.
I tried with an actual DIN keyboard and no luck either.

Out of all the PS/2 keyboards I have, only one provided an interesting feedback: a Microsoft RT2300 keyboard which has the NUMLOCK LED toggle on and off when I press the key. CAPS LOCK and SCROLL LOCK do not function though.

I opened the case and I'm afraid the connectors to the DIN input are dead, but I don't have any multimeter to check that. But then, I find it weird that a single keyboard has a working NUMLOCK LED.

I attached pictures of the area on the motherboard. At first glance, I'd say it's unfortunately dead but I would like to have more experienced people say what they think about it.

BIOS is an Award Modular BIOS v4.50G.
The motherboard seems to be a CHAINTECH 486SLB VESA REV.2 486.

Thanks.

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Reply 1 of 5, by jakethompson1

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My IBM PS/2 has a fuse on the keyboard connector and I blew it connecting a keyboard that had been wet. However, once that happened the LEDs wouldn't come on at all.

Given that the battery corrosion is right next to the keyboard connector it wouldn't be at all surprising if some of the connections are weakened or broken. At one time I would have said give up on it, but if you look through the threads here you can see some of the efforts people go through to fix corroded traces on their board. If you do give up on it you ought to at least offer it to someone for the cost of shipping.

Only other idea is if the keyboard controller is socketed try pushing down on it to reseat all the connections.

Edit: you may also be able to use a multimeter to check continuity between the pins in the AT connector and where they go to on the keyboard controller, try looking up its part number to find a datasheet that gives the pinout

Reply 2 of 5, by Deksor

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Remove that battery asap and clean the area with vinegar and then look for bad traces.
You may want to move out and in the keyboard controller right underneath the RAM slots too and maybe even check for bad contacts there.

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Reply 3 of 5, by Fox_McCloud45

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jakethompson1 wrote on 2020-07-04, 20:41:
My IBM PS/2 has a fuse on the keyboard connector and I blew it connecting a keyboard that had been wet. However, once that happe […]
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My IBM PS/2 has a fuse on the keyboard connector and I blew it connecting a keyboard that had been wet. However, once that happened the LEDs wouldn't come on at all.

Given that the battery corrosion is right next to the keyboard connector it wouldn't be at all surprising if some of the connections are weakened or broken. At one time I would have said give up on it, but if you look through the threads here you can see some of the efforts people go through to fix corroded traces on their board. If you do give up on it you ought to at least offer it to someone for the cost of shipping.

Only other idea is if the keyboard controller is socketed try pushing down on it to reseat all the connections.

Edit: you may also be able to use a multimeter to check continuity between the pins in the AT connector and where they go to on the keyboard controller, try looking up its part number to find a datasheet that gives the pinout

I doubt it's the fuse since LEDs come on, yeah.

I don't have a multimeter and I believe I've already spent too much money on trying to get that thing working. But I honestly think those connectors are what's up.

Reply 4 of 5, by jakethompson1

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Multimeters aren't that much, looks like there's a cheap Harbor Freight one for $6
It's just a box with two probes and a dial to set the mode, and an LCD screen with the readout - not like an oscilloscope or anything

Reply 5 of 5, by Fox_McCloud45

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Deksor wrote on 2020-07-04, 20:48:

Remove that battery asap and clean the area with vinegar and then look for bad traces.
You may want to move out and in the keyboard controller right underneath the RAM slots too and maybe even check for bad contacts there.

I gently pushed down the controller to reseat it.

Unfortunately the motherboard does not POST anymore. I rebooted it and it only displayed preparation info (Trident etc.).

I rebooted it again and there's no VGA output now.

I'm pretty sure I broke something so there goes that.

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