Recently I managed to damage two 5.25 unidisks. In both cases after I reassembled the drives I notice the disk spins but the drive head no longer moves.
Using a 3rd working drive I was able to narrow the issues in both cases to the unidisk analog board.
I started by looking at the drive that has the same board as my working one - luckily the ic's are socketed so I was able to rule them out quite easily by swapping them over.
Next using Sams ComputerFacts - Disk Drive Apple II as I guide I checked the voltages at the transistor (Q2) and found E - 11.9 / B - 0.63 / C - 0.62 which according to the documentation doesn't sound right.
I would like to change the transistor however I don’t know what an available equivalent would be – the existing part no is B1080
Any assistance would be greatly appreciated.