Does the PSU works when not connected to the mb?
I don't see the battery. Some mb refuse to work without them...

Unrelated... but, 'interesting' looking extra slot near that 8-bit ISA connector. Wonder what it is.

Edit: Ah, proprietary memory card.

I can see that you connected external battery. Is the battery polarity correct?
There are two oscillators and JP8 to choose between them. Try to close it if it's not or to open it.
Does the CPU getting wormer after start?

There are two oscillators and JP8 to choose between them.

No, one of those oscillators is for the coprocessor socket. The JP8 is for choosing 1:1 or 2:1 frequency from the CPU oscillator... i.e., a 50mhz oscillator could either run the CPU at 50 or 25mhz, depending on the JP8 setting. And an incorrect setting wouldn't prevent the thing from turning on at all, it just wouldn't make it all the way through post if it was set too high, and it would work fine but run the CPU slower if it was set too low.

I would first go over the thing with a magnifying glass and look for damage... especially around the mounting holes. Sometimes screwdriver nicks can be hard to see. Then take a multimeter to the pins of the power connector, see if any of the voltage lines have a dead short to ground. It's also possible there's an issue with the 'power good' line. I'd try tracing that out, and see what you find. Some boards have a jumper that switches it between 'signal detect from PSU' or 'signal detect from board', which could be one of the undocumented jumpers on yours... it'd usually be a three pin jumper somewhere near the power connector if your board has such a thing.

Could be a case of shorted tantalum capacitor. Use an ohmmeter to check the resistance on the different power lines.

Thanks for the replies, much appreciated.

Yes the PSU works fine, well and truly test that.
Yes that extra slot is for a memory card apparently; I don't have it but the documentation says that it's optional.
I'll check that the battery is connected correctly, I didn't realise some boards won't even boot without it. I've never seen a board that won't even beep at me.
I've tried opening and closing Jp8 with no difference, and infact I've toggled most of the undocumented jumpers just to see if I get any change.
If I still have no luck then I guess it's time to break out the multimeter...

thanks again!

I didn't realise some boards won't even boot without it. I've never seen a board that won't even beep at me.

I've never seen a PC motherboard exhibit such behavior either, but I guess it's possible... I know some of my old 68k Macs are finicky like that.

I've experienced something similar (PSU won't spin its fan, but would slightly buzz instead) with a 386 board after inserting the CPU wrongly oriented. It doesn't seem to be the case in this photo though...

Old Thrashbarg wrote:

I didn't realise some boards won't even boot without it. I've never seen a board that won't even beep at me.

I've never seen a PC motherboard exhibit such behavior either, but I guess it's possible... I know some of my old 68k Macs are finicky like that.

I've seen this situation occur when the MB was grounding out.

Yes, but grounding out is a different problem entirely. What I meant was, I've never seen a PC motherboard that wouldn't boot as a direct result of a dead/missing clock battery. Many will throw an error about a low battery or incorrect clock settings or whatnot, but they'll still at least power on and make it through POST.

I have an AMI Mark V Baby Screamer 386 board which would not turn on because it did not like the RAM for whatever reason. I swapped the RAM with another type and it worked fine. I noticed that you only have 4 modules inserted. Try filling all SIMMs with 1 MB pieces.

The PSU not fired up sounds to me like a short or ground issue. Perhaps this board is expecting a GND on one of the mounting holes. What happens if you put the board in a case?

I had an ATX PSU which did not turn on like this. I tried everything I could think of, including some silly ideas. For whatever reason, the board did not like one of the motherboard stand-offs. The stand-off was dead centre and had no visible possibility for a short. I even tried an insulative washer on the top. I ended up removing the stand-off and the PSU/motherboard fired right up. The symptoms never returned.

If you are testing the board in a case, try removing it. If you are testing the board out of a case, try putting it in one.

Old Thrashbarg wrote:

Yes, but grounding out is a different problem entirely. What I meant was, I've never seen a PC motherboard that wouldn't boot as a direct result of a dead/missing clock battery. Many will throw an error about a low battery or incorrect clock settings or whatnot, but they'll still at least power on and make it through POST.

I have. An Intel motherboard. At first i thought that it was a dead motherboard. When i replaced the battery it powered up just fine.

In my experience with 68k Macs and other odd pieces of hardware where the RTC battery can cause non-booting symptoms it's almost always due to the partially or totally dead battery being in-circuit and dragging the voltage down or something along those lines. With a good battery or no battery altogether the system boots up fine, but with a depleted battery in place it doesn't work.

Thanks for the ideas but I've tried it in / out of different cases, with no RAM, with a full bank of different 1mb sims. With battery, without battery. Different CPU's. With cache, and without, etc. Still nothing - hasn't beeped once.

I deem it dead unfortunately, so onto my wall of lost hardware it goes (in the outdoor toilet).

Thanks again for the ideas though, I'll have to keep that grounding issue in mind in the future. I didn't realise this could be a problem - would that be poor design, or a fault? Shouldn't the GND wires in the PSU's motherboard wires deal with grounding the motherboard?

So you are not checking the power lines for shorts? Maybe only one of the capacitors has to be removed.

I've spent enough time on this thing now. It's time to move on.

I have another ISA 486 board that I can use instead, the only downside being that it doesn't have a turbo button option. But then again I don't think I've ever really used the turbo button for anything constructive, and I can always turn the cache off.

Thanks again all for taking the time to reply.

Going to revive a dead thread because I'm just that kinda guy... right?

I swear I've hunted all over the web trying to solve the exact same issue on an Asus PVI-486SP3
Cleaned every contact, followed the traces I could... Damn I've looked at everything you can think of.

PS is definitely good. Vid cards I've tried are good, multiple CPUs, reseated/cleaned all cache & bios chips, new bios battery - the whole 9 yards.

After every test under the sun... BOOM!!!

A tantalum just sent my heart racing and blew clear off the board!!!
Guess I found the dead cap? Haha! Boy my heart's still going... that was loud!