The point you observe the hang is when the BIOS does the latest steps of the POST. At that point, ROMs from Controller Cards (like Network, SCSI) get initialized and the settings from the Advanced Chipset Setup get applied. If your RAM or cache timing is to aggressive, or your tag RAM is broken, you may observe behaviour like that.

Try disabling L2 cache and setting maximum wait states in the chipset setup.

Good tip there, unfortunately I did that;
1 loaded optimum settings, set auto config on so no aggressive wait states
2 disabled internal external cache
3 actually moved the tag cache chip + all my cache to my backup board as it didn't have cache.

My backup board is now in the system and working, so it has the same ram, cpu, cache+tag and hard drive as the original board that fails boot.

But what you said about roms from controller cards getting initialised is interesting. Since hard drive error 20 is all I can go by, could this be a failure trying to initialise the onboard hdd controller?

Is it possible to disable the onboard hdd controller?

Just skimmed through some specs and manuals, it looks like the UM8663BF is responsible for eide

treeman wrote on 2022-04-18, 11:53:

But what you said about roms from controller cards getting initialised is interesting. Since hard drive error 20 is all I can go by, could this be a failure trying to initialise the onboard hdd controller?

Is it possible to disable the onboard hdd controller?

If you get to the message "hard disks fail (20)", the onboard fdd + hdd initialization is over. If the system locks up after showing you that message, it is not related to HDD initialization. The onboard hdd controller has no dedicated ROM, the IDE support is part of the mainboard ROM and already initialized slightly earlier.

IIRC you can only disable the second channel, but not connecting any HDD should be close enough to disable the controller for all practical troubleshooting purposes.

treeman wrote on 2022-04-18, 12:16:

Just skimmed through some specs and manuals, it looks like the UM8663BF is responsible for eide

It's not. The EIDE interface on the 8433UUD is part of the south bridge, the UM8886. The 8663 is an ISA super-I/O chip that is used for parallel, serial and floppy interface. While that chip might be able to do ISA-based IDE, too, the MB-8433UUD doesn't use that capability. The speed of the PCI-connected southbridge-integrated IDE is way higher than the ISA solution would be able to achieve.

I see, thanx for the great explanation. I guess back to start then I'll try to figure out what else could be locking it up while loading

I now started getting the same issue on my second motherboard. I was thinking about the rom initialisation so took out the sound card and it started booting. Could it be the sound card or it is luck? It is a isa sb16