I think in these old computers the 5.25" drive was usually configured as A: and the 3.5" as B:

Can you show a picture of the BIOS floppy settings?

I kindly disagree, what decide what is A: and B: is how flppy are connected, I tried to set the 1.44mb as b and I get an error message.

Error:

My settings (no error but the problem described before):

I have been told that the problem could be a drity data bus, I tried to clean the card contacts with pencil eraser, change the isa slot, disconnect the serial\parallel port but no changes.

What happens if you use the original black 3.5" drive?

Nothing, I can set it as 720 or 1,44mb the led turns on but it doesn't read the floppy (I have 1,44mb floppies only).

Do you have any other floppy cables? I suspect that PCB adapter is causing the problem.

I do, but that would make 2 floppy cables non working, since with my floppy drive I use my floppy cable, I do not know if I have more because most of them have a pin with closed hole while such cards have all the pins.

Edit: tried a third floppy cable with another floppy drive, same behaviour... not boot disk with weird characters.
The problem is somewhere else

OK, you're not using the PCB. (I was trying to figure out what those jumpers on the PCB do.)

No key means cable might be oriented incorrectly. Make sure the red wire is closest to pin 1.

Thank you, the cable is properly connected.
I may give a completely different try.
I have an ISA floppy ide card, that wouldn't make the original hard drive works but it would let me verify if the problem lies on the mfm\floppy card or on the pc itself.

Bad news everyone!I installed the isa card with cf adapter, thanks to xtide I was able to boot the cf card, pc seems to work fine in such configuration...
Now... any suggestion? Is the mfm card broken then?

Can you show us the floppy and hard drive controller cards? Are there any jumpers on the floppy card?

The controller card is an Everex EV-332. I found the settings here:
https://stason.org/TULARC/pc/hard-disk-floppy … ves-EV-332.html
There are no populated jumpers, it has 3 cables:
J1, J2 and J4
From what I understood J1 and J2 are cables that need to be connected to the hard drive, while J4 is for the floppy drives.
I tried to connect my surely working floppy drive to that card and it doesn't work.
To me the problem seem the card, that being said it's in pristine visual condition, here is a picture:

Problem is, if you replace the controller card you will lose all data on the hard drive.

Have you tried putting the original 5.25" drive back, i.e. everything in original condition? Maybe it needs the two floppy drives, IDK.

Get hold of DD 3.5 floppy disks and see if the black drive works with them. Also see if you can get the system to boot off the 5.25" drive.

Install batteries too.

I'm actually unable to do any other try because while trying to get the cpu in the socket (after take it out to clean the contacts), I've broken an address pin line of the cpu.
Now the computer is obviously dead.

L O L, too bad. I recently broke a pin on a 1.4 GHz Tualatin Celeron removing it from a system, which annoyed me greatly as these things are no longer cheap. However it's only a corner VSS pin so it should still work OK.

yes and if you have the skill you can replace it, while for the 286 it's impossible, I already ordered a replacement btw.

So we are back on business good people.
Where we were?
The mfm card seems to be the problem since with an eide sd card the pc booted fine without any visual glitch.
It's the only mfm card that I have (and do not plan to buy another just for this pc).
Any test I can do to check the mfm card only?

Nemo1985 wrote on 2023-02-07, 20:59:

yes and if you have the skill you can replace it, while for the 286 it's impossible, I already ordered a replacement btw.

While the pin is broken off, you can still solder a new pin to the side of the chip where the broken off pin was located. while it won't be very sturdy, it should make the cpu still usable.
easiest way to solder it on would be to put the cpu back in the socket, put a piece of wire, like the cut off leg of a new resistor or new capacitor, in the socket where the broken pin was
and solder it to the side of the cpu.
There will always be some metal left to solder it onto.

I already bought a new 286 cpu and mounted it, the old one had almost none metal left on the broken pin:

plenty of metal left for a fix - you dremel out the plastic above to uncover it 😀

rasz_pl wrote on 2023-02-22, 01:49:

plenty of metal left for a fix - you dremel out the plastic above to uncover it 😀

With the new cpu the behaviour is even more erratic, most of the times the pc doesn't boot, the diagnostic card throws random numbers, while with the old cpu it was booting consistently.
If I ship the cpu to you, would you repair it, please?