Ideas for further debugging faulty drives? \ VOGONS

Ideas for further debugging faulty drives?

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First post, by Inrit

Posted on 2024-07-17, 02:07

Inrit Offline

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Hi there,

I have a 486 that was working well for years, until recently the 3.5" floppy stopped working, and then the HDD stopped working (now won't boot). The AMIBIOS configuration cannot detect the HDD values either, whereas it previously could.

The machine has a real 5.25" floppy and 3.5" floppy, and a CF card to IDE adapter with a 512mb card for HDD.

I have tried:

Replacing the controller card
Replacing the CF card adapter
Touching up all the solder joints on the original controller card, cleaning its contacts, and trying it again
Moving the new controller card to a different ISA slot
Booting off a DOS 3.5" boot floppy

None of these helped until I moved the controller card to a new slot. When I did that, the BIOS configuration once again was able to auto detect the HDD values and after saving those, the machine started to boot into Windows 95. However, partway through startup it failed with a blue screen of death saying the C: drive was not writable. When I rebooted, the BIOS configuration could again not detect the HDD.

So that's when I decided to try booting off a 3.5" floppy (the drive light went on after each boot). But that failed, saying the disk was not bootable (I know it is).

What could be causing this set of problems? It all seems related to the controller card, but I've now completely replaced that, as well as the CF card adapter. Not sure where to go next, since that already seemed like the nuclear option!

Would love any ideas.

Thanks!

Reply 1 of 11, by dominusprog

Posted on 2024-07-17, 03:00

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Are you using an ISA riser? If so, post a photo of the riser.

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Reply 2 of 11, by Inrit

Posted on 2024-07-17, 03:02

Inrit Offline

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dominusprog wrote on 2024-07-17, 03:00:

Are you using an ISA riser? If so, post a photo of the riser.

No riser. If it helps, the motherboard is an Abit AT4.

Reply 3 of 11, by Deunan

Posted on 2024-07-17, 08:35

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No battery damage on that mobo? It sound like you have some ISA bus problems.

Reply 4 of 11, by Inrit

Posted on 2024-07-17, 11:55

Inrit Offline

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No battery damage at all, there was never leakage and I replaced the old battery with a safe one long ago.

What would be the best way to diagnose any ISA bus problems?

Reply 5 of 11, by rasz_pl

Posted on 2024-07-17, 11:57

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power supply

https://github.com/raszpl/FIC-486-GAC-2-Cache-Module for AT&T Globalyst
https://github.com/raszpl/386RC-16 memory board
https://github.com/raszpl/440BX Reference Design adapted to Kicad
https://github.com/raszpl/Zenith_ZBIOS MFM-300 Monitor

Reply 6 of 11, by Inrit

Posted on 2024-07-17, 12:57

Inrit Offline

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I just tested the output from the power supply, from the connector going to the motherboard.

The 5v and -5v are just about spot on, the 12v is 12.4v (which I imagine is close enough), but the -12v is -11.4v.

Could that be related, or is it likely a red herring?

Thanks again.

Reply 7 of 11, by kotel

Posted on 2024-07-17, 13:19

kotel Offline

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Maybe a bad BIOS chip?

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Let that be our legacy."
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Reply 8 of 11, by Deunan

Posted on 2024-07-17, 13:57

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Inrit wrote on 2024-07-17, 12:57:

The 5v and -5v are just about spot on, the 12v is 12.4v (which I imagine is close enough), but the -12v is -11.4v.

These are good. 12V will be a bit higher if there is no load - and without a mechanical HDD there won't be on 486 mobo. -12V rail is usually rather poorly regulated anyway and yours is still, if barely, within 5%.

Was the CF card still installed when you tried to boot from the floppy? Try a pure floppy boot, disconnect everything HDD related (including any cables from the controller). It's not impossible that you have 2 separate issues there, one is HDD and another is some floppy drive failure. So it's best to try to get at least one of these things working and take it from there.

Reply 9 of 11, by rasz_pl

Posted on 2024-07-17, 14:06

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PSU can produce nice voltage with no load, but terrible drops when something tries to actually draw power

Reply 10 of 11, by darry

Posted on 2024-07-17, 14:18

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rasz_pl wrote on 2024-07-17, 14:06:

PSU can produce nice voltage with no load, but terrible drops when something tries to actually draw power

That and ripple.

Reply 11 of 11, by kotel

Posted on 2024-07-17, 15:10

kotel Offline

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Try a different power suply.

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