If it is OK after warming up, what is the ambient temperature in the room when you turn it on? I know cold affects some systems, but as I keep constant temps at home I never have that issue.

Marginal capacitors tend to perform closer to spec once warmed up. Could be an explanation .

I have a server which is difficult to start in cold weather. The CPUs aren't detected. I have to take off the side panel and push the CPUs down and wiggle them about in their sockets for them to be detected.

In summer it starts without issue. I guess contacts are looser in cold weather.

The room temp was normal (21'C) but the PC may have been cold last couple times I've tried - it's winter and it gets cold in here!

Playing with it last night and it seemed to be getting worse... It had been on for a couple hours and I still get maybe 1 in 4 key presses doubled up. I've tried scrubbing the motherboard around where the keyboard connector is with contact cleaner but if anything it's worse for a little while after doing that! I can't see any physical damage or corrosion or anything around that corner.

I don't have another PS/2 keyboard to hand to test (have one on order), but this one tests fine in another PC (an old ThinkPad) so I don't think it's the keyboard.

Thing is that worries me is that I did a BIOS update soon after receiving this PC and it didn't seem to have this problem back before I did it. It might be a coincidence, or it might not. I can't downgrade back to the version it was on before - it doesn't seem to support going back a major release. I'm sure the BIOS is stable though as it was a very common office PC back in the day. I was on v1.o5 when I got it and now I'm on latest 2.02.I can go back to 2.01 easily enough but the issue is still there.

Today I turned it on this morning and it did the same thing, but left it alone for an hour and it's absolutely fine now. Maybe I'll have to take a closer look at these surface mount capacitors all over the place...

Cheers,
Steve

Oh well I was just playing with it, did a reboot and saw only half the RAM was counted and it hung. It won't come back on any more - it's dead! I don't even get any beep codes. Tried swapping RAM and CPU but no good 🙁

Gave the mobo a proper scrub clean and gone over every centimetre, found a manufacturing defect of a capacitor not soldered properly but that's not it. I can't find anything obvious 🙁 Back to eBay then!

Maybe a dry solder joint somewhere? I have a board that is completely lifeless (---- post code) but if I put pressure on the chipset it starts going through the post.

I've been pushing it and twisting it all ways! Once in about 20 boots with no RAM in I can get a beep code telling me no video!

I'm wondering if another AST motherboard off eBay will fit as I can't find the exact one. It's the riser card I'm worried about

I think I'm gonna try make this 6 simm board work. The mounting points look the same, and the riser slot is in the same place (lined up with right hand screw hole on left hand COM port), I can make some auxiliary AT power connector up if needed, and this one has onboard audio so if the riser card doesn't work I still have sound and video. The picture's poor on eBay though so hard to see - I think it's a socket 5 or 7! The other picture is the existing board I have.

I have found that a failing hard drive can dramatically slow booting. Had a drive fail recently that extended boot time on my FM1 system from 35 seconds to 150 before it finally died. It didn't affect anything after booting though.

OK I've made some progress with the original board. It must have had a corrupt BIOS or something as the beep codes I could once-in-a-blue-moon get it to do I finally discovered were telling me it wanted to update the BIOS (thanks to this amazing site - https://matrix.home.xs4all.nl/beeps/ast.html), so I reflashed the latest BIOS and I got a POST!

Now how did I get it to POST and do the BEEP codes? By heating up the motherboard! If I apply lots of heat (30 seconds from a small 1000w fan heater - everything there almost too hot to touch) to the top right of the motherboard (rear right of the PC) only this area then it boots, and once booted it stays booted. Now I still get some repeated characters when pressing keys (I got a new keyboard to confirm it's the PC and not the keyboard) until the PC's been running for ages, so could a faulty keyboard controller stop a PC booting? Is it one of these chips as the keyboard controller is one of the silver things far right of the image. What's the 1977 copyright Intel chip? I can see the other main ones are the BIOS and floppy controller.

Is it worth sticking the whole board in the oven (wife permitting!) to see if it needs a little reflow?

Cheers,
Steve

Just checked then and double keys (in DOS or BIOS or just crashes Windows) and it literally stops doing it if I heat that area while the PC is running and I'm typing.

Yep traced a PS/2 keyboard pin back to the Intel 1977/AST 1994 chip labelled "237021-902" but I can't find any info on that chip!

The SMD caps look OK but I've just ordered a load to replace them. Not sure I can bring myself to do the 'twist off with pliers' method some people use!

OK I've recapped the board but to no avail, still the same. However I've been playing with heat again and I've been making cardboard ducting to apply heat to particular chips! The culprit is the BIOS chip! This kinda makes sense as as few times I've had the beep codes saying it needs to flash. It only seems to want to work when it's about 45'C or hotter!

All these problems seems to start around when I did a flash update too....

Question now is though if I buy a blank one, can I flash it in the board using the force flash jumper setting? How can I remove the old one and solder it in without a hot air gun?

It's an Intel N28F001 BX-T150

Cheers,
Steve

Have hair dryer or heat gun? Gently warm the power supply then try again, if not, Heat one chip at a time on the motherboard and try. If not, heat another chip then try. So on.

Cheers,

pentiumspeed wrote on 2021-01-10, 23:27:

Have hair dryer or heat gun? Gently warm the power supply then try again, if not, Heat one chip at a time on the motherboard and try. If not, heat another chip then try. So on.

Cheers,

Yeah I found it was the BIOS chip and I don't have the tools or equipment to replace it 🙁

But good news! The replacement motherboard from eBay fits! Just needed to drill two holes for the audio sockets in the back. Thanks AST for keeping your motherboards to standards. So now I have an AST MS-T 5100 motherboard inside with a P133 CPU so it gets a little speed boost too. Only problem is the old riser card doesn't fit so I can't put any PCI or ISA cards in. This board has a sb16 with a Mach64 videocard onboard though so all good. I can't have an ethernet card which is a shame but the IDE-SD adapter will let me get files across easily enough.

Cheers,
Steve

I've knocked up a video of the 'fun' I've had with this PC https://www.youtube.com/watch?v=bNTd069iwZ4