Congrats on the 486 board!

One question, your ATX->AT adapter, did it have two extra wires that led to no where? If so, those have to be connected to each other (or an ATX-style power switch) to tell the PSU to power on. My PSUs appear to work just having those two wired together, but I think some ATX PSU's need a momentary bridge, so the wired-together might not work.

Reason this is relevant is that AT style PSU's had a master on/off physical switch, ATX can be turned on/off via a front case button, usually connected to the motherboard itself. The way this works (IIRC) is the motherboard connection is directly wired to the two pins the ATX->AT adapter has wires for, thus allowing the switch on the case to close the circuit for the PSU, telling it to power up/down. AT motherboards don't have this.

The nice thing about this setup (if the wires can just be permanently connected) is the PSU switch itself then works like an AT-style power switch.

Try connecting the two wires together, briefly, or permanently. Only do this if the adapter had those two extra wires though, as obviously connecting two random wired might not give good results 😀

Thanks for the thought - yes the ATX->AT adapter has the 2 extra wires with a latching switch to turn on the PSU, i have a fan connected to it so I'm sure its on and putting out power.

While I have no idea as to your problem, I would like to thank you anyway. Reading your post made me realize how to deal with my 1993 PSU in my working 486. It never occured to me that there may be ready converters for this. But thanks to you, I found one on amazon and ordered it.
I rather test it when knowing the board is fine, than after a PSU meltdown with unknown follow-up damages.

Did your board come with cpu and ram or are these additional question marks?

Does the board have a power led or anything that indicates electricity present?

Did you install a beeper?

I dont have a beeper on hand, but will order one. No LEDs or anything on the board.

Everything is a question mark including me 😀 I've reasonable confidence in the board due to the seller, and I've tested the PCI video card in another system.

This is my only socket 3 board so the RAM / CPU were purchases for it.

J3 seems to have power led according to the manual. You need to connect an LED to it correctly though.

Pin1 is signal, pin3 is ground

ux-3 wrote on 2024-05-19, 13:42:

J3 seems to have power led according to the manual. You need to connect an LED to it correctly though.

Pin1 is signal, pin3 is ground

Nice spot, I've hooked up a LED to it and it does indeed light, so confidence in the board is fairly high.

CPU isn't rotated?

First where i will start is cleaning the board.. Seems to be to dirty.

Does the little heatsink south of the CPU get hot during operation?
If you have access to a multimeter, check the voltage at this heatsink.

Beeper is definitely your 1st step. Good chance the PC is trying to tell you whats wrong by giving you a beep code that you have a ram/video/whatever error
Even a cheap piezo buzzer will do. (proper speaker is preferred if playing PC speaker games though)

https://www.ebay.com.au/itm/182990065587?_trk … 5.c101506.m1851

Little update, both my Beeper and POST board arrived. The beeper gives a continuous stream of beeps, and the POST board says C6C1 which seems to mean an external cache error.

From my read of the manual it seems like the board requires all 4 cache slots + Tag RAM to be filled, so I suspect I'll need to buy some cache chips even to test which one might be at fault.