bibilit

A Classic II board will not be a bad option.

https://www.ardent-tool.com/IBM_HD/ddrs_spw.pdf

In your picture, you have got a jumper in position 2 (ID Bit 2) / 5 (Enable auto spin) but nothing on pin 6 (S/E mode) then a jumper on pin 7 (Disable Unit ATTN) So the default setting is LVD until the jumper is present. What is the brand and type of this drive ? you can probably find information online.

have a try with the jumper on, nothing to lose. Have you any idea where this drive came from ? probably connected to a Powermac G4 with a PCI SCSI card.

If the drive is S/E compliant i think it cannot be either HVD or LVD. S/E is Single Ended while hvD or lvD are Differential. https://www.datapro.net/techinfo/scsi_doc.html Of course if the drive is Differential type of some sort, won't work with any of your machines...

IIRC you should enable the S/E mode, so a jumper should be used on pin 6. I have used that kind of units at some point, but was tricky.

The internal drive is probably stuck. Grease is known for hardening with age, floppy carrier is unable to move or slide. Cleaning and lubricating is probably all that is required to get it working again. Yes, a small gear is prone to breaking, but can be found new.

Can be a bad shunt regulator, or just the same part goo contaminated. Happened to me often.

I will say also UE8 or UF8. In that area at least.

Not a big deal, rotating the yoke is pretty easy, done hundred times. Seen more issues with the yoke than with a screen misalignment, but not saying is not your issue here.

Ok, but have you the exact same issue when swapping Roms around ?? What happens when the "Bad" Roms are fitted to the "Good" board ?? (will not hurt the board) If not, the only issue i can see is that one of the logic chips handling the ram memory is bad, hence throwing fault codes related to bad ram when ram is ok and displaying weird display patterns ramdomly

Not at all, nothing in common.

Yes it is, what you see soldered are the sockets for the Optoisolator.

Fault code is related to a Ram issue, but this kind of behavior can also be related to bad Rom, as the Rom is socketed, i will swap Rom in the Good Plus to see if Rom is ok or not

Hard to say, can be anything from a bad trace to a sound chip. The Sound chip is on the Upper left corner (C28) label is SND. The chip is unlikely troublesome, but who knows, recently replaced one on a Macintosh Plus without sound and it came back afterwards.