This could be an IRQ or memory conflict between the card and something else, but the fact that the problem doesn't go away immediately after power off makes me suspect something more hardware-related.

Do you have another I/O card (ISA is fine for these purposes) to test with?

If you do, swap it out and see what happens.

If you don't, consider that a multi I/O controller like this is just a couple of independent chips on one card. Start by disabling all functionalities and see if behaviour continues. Then activate components (IDE, floppy, serial/parallel/game) one by one and see where it fails. When you know which component causes it, take a look at the settings of that.

It would be useful to know what else is in the system that could use memory addresses or IRQs (i.e. which other cards).

Also, never underestimate how weird the symptoms can be of a failing PSU; if messing around wiht settings on the card hasn't fixed it, testing with a different PSU could.

dionb wrote on 2025-02-13, 09:22:

This could be an IRQ or memory conflict between the card and something else, but the fact that the problem doesn't go away immed […]
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This could be an IRQ or memory conflict between the card and something else, but the fact that the problem doesn't go away immediately after power off makes me suspect something more hardware-related.

Do you have another I/O card (ISA is fine for these purposes) to test with?

If you do, swap it out and see what happens.

If you don't, consider that a multi I/O controller like this is just a couple of independent chips on one card. Start by disabling all functionalities and see if behaviour continues. Then activate components (IDE, floppy, serial/parallel/game) one by one and see where it fails. When you know which component causes it, take a look at the settings of that.

It would be useful to know what else is in the system that could use memory addresses or IRQs (i.e. which other cards).

Also, never underestimate how weird the symptoms can be of a failing PSU; if messing around wiht settings on the card hasn't fixed it, testing with a different PSU could.

Unfortunately I do not have another spare controller 🙁
I'll try disabling the individual functions to see if anything changes.

No other cards in the PC, just the CirrusLogic VLB Video card, and the I/O Controller VLB card.

Have another PSU that I can also test

Have disabled all functions on the I/O Controller, issue still exists. I guess its just a busted card...

Cheers,

dionb wrote on 2025-02-13, 09:22:

This could be an IRQ or memory conflict between the card and something else, but the fact that the problem doesn't go away immediately after power off makes me suspect something more hardware-related.

Agreed ... simple/quick test - reset the system without power-off... Does it stay hung, or start POST again...

Also, never underestimate how weird the symptoms can be of a failing PSU; if messing around wiht settings on the card hasn't fixed it, testing with a different PSU could.

Always worth checking, but I think unlikely ... how much "extra" load does this card make?
The fact that it runs perfectly without the 1 card doesn't seem like possible PSU to me.

(although at one time I did have a PSU fail in such a way that the system would die after a
few seconds with a hard-drive installed, but would boot/run from floppy just fine...
so you never know)

Dave ::: https://dunfield.themindfactory.com ::: "Daves Old Computers"->Personal

DaveDDS wrote on 2025-02-13, 12:28:

Agreed ... simple/quick test - reset the system without power-off... Does it stay hung, or start POST again... […]
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dionb wrote on 2025-02-13, 09:22:

This could be an IRQ or memory conflict between the card and something else, but the fact that the problem doesn't go away immediately after power off makes me suspect something more hardware-related.

Agreed ... simple/quick test - reset the system without power-off... Does it stay hung, or start POST again...

Also, never underestimate how weird the symptoms can be of a failing PSU; if messing around wiht settings on the card hasn't fixed it, testing with a different PSU could.

Always worth checking, but I think unlikely ... how much "extra" load does this card make?
The fact that it runs perfectly without the 1 card doesn't seem like possible PSU to me.

(although at one time I did have a PSU fail in such a way that the system would die after a
few seconds with a hard-drive installed, but would boot/run from floppy just fine...
so you never know)

Dave ::: https://dunfield.themindfactory.com ::: "Daves Old Computers"->Personal

Reset without power off did nothing, it remained in that locked up state with no POST.
swapped out the PSU with one from my working Pentium system and no change...

The fact that it doesn't die right away but needs 20-30s of warmup, and that it stops responding to reset afterwards, would suggest to me a thermal issue. There's usually 3 things that react to temperature and can cause that:
- solder joints, and possibly micro-cracked traces and vias
- the chips themselves
- capacitors

My money is on the first item on this list. First clean the edge connector as VLB is notorious for having bad contact. Also make sure the is no corrosion or dust (or any other unwanted stuff) in the slot as well. Use compressed air, perhaps along with some IPA to wash it first, to clean it. Do not use any abrasive methods to clean the contacts in the slot, the gold plating on these can be very thin and easily damaged.
If cleaning does nothing start looking for scratches and other damage on the card. Especially the main chip(s) - any bent pins and/or corrosion (dull, grey solder) is suspect.

I've had a few instances of I/O chips going flaky and on inspection the pins and solder looks rough and dull grey or even white powdery corroded. Reheating the solder has fixed them. Maybe some metallurgical imbalance between factory "tinning" and assembly solder that shows up in decades.

Finally got a replacement I/O card, PC now working without any issues 😀

Thanks all 😀