Disk II PROM differences?

[carlsson]

A while ago, I brought home a defective, clone Disk II controller card. I compared it with the clone controller card in my Basis 108, and the two looked similar enough. As a crude form of troubleshooting, I pulled 74LS chips from the defective card and tested them in my TL866CS programmer. All the ones the device supports, it reported as OK. The rest of the chips, I swapped matching chips between the working controller and the unknown.

 

When I swapped the two PROM chips, 7649A, I got garbage on screen when trying to access the drive.

 

Now it was a while ago, I didn't take exact notes and my memories are hazy, but should I assume that all Disk II cards and clones of thereof, are using the same PROMs? There were some small differences in number of resistors, capacitors etc too between the two cards.

 

At some point near in the future, I will do a bit more thorough testing and document what I'm doing so I can get hints how to fix the broken controller. Actually I think there may be another broken controller somewhere, but I'm not sure about that.