Over the weekend I tried to revive a PS/2 Model 80 whose CMOS battery died (after 25 years!). Finding a replacement battery fortunately isn’t difficult (6V lithium “photo” battery), but recreating the configuration information of course requires a reference floppy and the .ADF files for any non-IBM adapters installed in the system.
The early PS/2 implementation of Plug and Play leaves something to be desired. Keeping a reference diskette with a system for many years turns out to be difficult in practice. Newer PS/2 systems with a reference partition do not suffer from this problem but still need floppies if the hard disk dies.
Finding a Model 80 reference floppy image or the ADFs is not difficult, but the system just kept refusing to boot from my floppy. The diskette was readable in other systems and I tried several of them, both original IBM floppies and self-made copies. None of them worked. The drive was spinning, did a few seeks, and then the system showed an error.
I tried and tried many times, and just when I was giving up, the system booted up from the floppy! Of course I was missing an ADF or two, so I had to modify the floppy—it doesn’t help that the reference disk only says that configuration information for adapter in slot so-and-so is missing, and doesn’t indicate what device is in that slot. But the number of MCA adapters is limited and identifying the cards is not too hard.
Anyway, after updating the floppy, I had the same problem booting from it. This time I took the drive out and noticed that when it spins up, there is a noticeable wobble. I assume the drive was not spinning at a constant speed and that caused reads to fail.
After retrying many times, the drive somehow settled down, completely stopped wobbling, and started reading without any errors.
It’s not clear to me what the problem might be. At first I thought it was a mechanical issue but now I’m convinced it is not. More likely it’s a problem with the drive’s motor which causes it to run unevenly. I don’t know if it needs to warm up or something but the drive always eventually started working, and after power cycling the system it was wobbly and failing to read again.
Is this some sort of typical floppy drive problem? The PS/2 floppy drives unfortunately use non-standard connectors and cables and can’t be replaced with standard PC/AT style parts. So the drive would be worth repairing… if I knew how.
Update: Forgot to mention that the floppy drive does not report any errors during POST. That indicates there’s no problem with the stepper motor/head movement.