Do all the chips look OK as well (no corrosion, rust, broken pins, and so on)? I looked at the photos and they look pretty good, but, it's hard to tell. As I stated, it could be a bad or corrupt BIOS. The one Intel chip next to the CL-GD5428 is the microcontroller that controls the DMA, Interrupt, and/or Polled Operation supported: http://pdf1.alldatasheet.com/datasheet-pdf/vi … L/N82C42PE.html

Also, change J28 to pin 2-3, and is your CPU a DX2-66?

Yes the CPU is DX2-66
Changed J28 to 2-3, no effect

I wonder what does this mean "J28 P24T or S-series reset control "
The default setting is 1-2

bjwil1991 wrote:

The one Intel chip next to the CL-GD5428 is the microcontroller that controls the DMA, Interrupt, and/or Polled Operation supported: http://pdf1.alldatasheet.com/datasheet-pdf/vi … L/N82C42PE.html

I'm not so sure. The datasheet says "SLAVE MICROCONTROLLER 82C42PE - Phoenix MultiKey/42G firmware, Energy Efficient KBC solution" and "DMA, Interrupt, or Polled Operation Supported".
So it just supports (doesn't control). DMA and Interrupt controllers are in OPTI 82c895.
Sometimes DMA controller is broken so FDD doesn't work properly.
ahtoh, could you upload here the oldbios.bin from your recovery floppy. Do you think the oldbios.bin was flashed into the bios chip during the recovery procedure (with the final 4 beeps)? And did the computer change its behaviour after the bios recovery?

Here is the recovery disk content attached.
Yes I did get 4 beeps in the end, this makes me believe that the bios has been successfully recovered.
It did not change anything though.

I was able to boot from Freedos boot diskette today.
And it looks like I can execute commands.
"Dir" seeks the drive
Also tried "echo test > test.txt" and the file was successfully created

update: not able to boot anymore. Looks like it warms up and no longer boots after a few minutes.

It's difficult to say what is faulty for sure: the onboard video or the chipset or whatever. I hope the POST card will clarify. If you had an ISA videocard it would be a little bit easy. As option you can try to check some discrete components of onboard video (resistors, chokes), measure resistance of VGA signals to ground rail and compare.
I looked into the oldbios.bin. It's early version than in the PB450ISA.ZIP (11/17/94 vs 03/20/96)
The phnxdeco.exe utility (you can find it here) can't list a structure of the PB450 BIOSes (I've expected to find a module of VGA bios)

I tried to flash the bios from PB450ISA.ZIP while I was able to boot
I typed "Phlash", hit enter, and I get multiple beeps in two different tones, and then computer restarted

Now I'm thinking about some test program that I can run without typing too much or completely unattended that would output results in a file.

I'm sorry but I don't know such programs. I usually use Checkit or Ndiags but they are interactive.
Unix-like OSes can give access through a RS232 null-modem serial cable but I don't know if there are so tiny 32bit distros that would be good for floppy

Here is a report from diag.exe:

Shows incorrect CPU speed

ahtoh wrote:

Here is a report from diag.exe:
Shows incorrect CPU speed

Does "Turbo" key present and active ?

Also the DIAG shows

1Monitor label:                           No Monitor
2Monitor type:                            B/W

If it's possible check resistance of chokes L5, L8-L11. They seem connected to VGA

Turbo key is depressed.
No monitor was connected

OK I connected a monitor and ran it again.
What did change was not the monitor, but BIOS Manufacturer and checksums!

I have no idea how they could be tied.
But what about:

ahtoh wrote:

Looks like it warms up and no longer boots after a few minutes.

If it's still true You can cool chips one by one using a special freezing spray or just a bottle tin lid with ice inside

I now suspect it is the BIOS chip that is at fault, because it gave me two different checksums.
I wonder if there is a program that can dump the bios to a file, so I can compare with one I flashed with Phlash.exe.

The phlash should have an option to backup bios. The uniflash can be handy too, altough I don't know if it supports such old chipset. But it's better to change the suspect chip to spare one. In case you haven't got a flash programmer there is the hot-swap method.
But failure of the bios chip can't explain the weird cpu speed 9.14MHz ( IMHO).
I have DX2 CPU and OPTi 895 mainboard in hand so I'll try to run the diag v4.47 this week. I hope this utility is easy to find.

phlash is not able to save the bios, at least there are no command line option for that.
looks like it is very early version
google DIAG447.ZIP

ahtoh wrote:

Yes the CPU is DX2-66 Changed J28 to 2-3, no effect […]
Show full quote

Yes the CPU is DX2-66
Changed J28 to 2-3, no effect

I wonder what does this mean "J28 P24T or S-series reset control "
The default setting is 1-2

The P24T cpus are overdrive chips I think.

Here's how the jumpers look on my 'working' one

Though my system has a DX2-80 and the bios reports it as a DX4/100, I think it's running at DX2-66 speed.
I could run the same diagnostic on mine, since it's all set up right now (just waiting for a hard drive), is there anything involved with getting diag.exe to run from a floppy?

here is the image of the boot disk I used
start diag, choose "create report file" in the right bottom menu.
this will generate text file diag.rpt, rename to .txt

p.s. there is nothing special about this diag, it's just random program I found online.
There might be better alternatives

An old utility to save bios GETROM.ZIP

(from the manual) wrote:

A typical session is described below for an AT.
1. Run the command "romsavat". This will produce a file called "atrom".

As I promised - my diag447 reports (am486dx4@100 and am486dx4@66)
Also I tried the GETROM.ZIP - it works. I ran it twice and compared the images. They have difference in one address (just 1 byte). I don't know why it is, but it means that different checksums of bios could be generated even in a working system.
The uniflash 1.47 doesn't work with a message something like "can't find PCI"