I desoldered the 6502 and stuck it in a working Apple II, and sure enough the Apple would not run with the 1581's CPU. I installed a replacement 6502 in the 1581 and I'm happy to report that it now works properly again! I believe this is the first time I've run into a faulty CPU in a vintage computer (or peripheral).

A couple of weeks back I wrote to the list asking for advice on fixing a C1581 drive (and thanks again for all the suggestions!). I now have the drive working again so I thought I'd detail my experience in case it helps someone else... Symptoms: Both LEDs (red & green) stuck on constantly, no response from drive via serial port. Drive does seek back to track zero on powerup. Power supply good. Initially, I had assumed that because the drive was seeking back to track zero on startup, that the CPU was running properly. (I later discovered that this is actually incorrect -- the 3.5" drive unit in the 1581 (an 800K unit identical to those used in the Amiga 500) does this operation itself when it is powered up.) The CPU's clock pin was pulsing so at least -something- was running. The EPROM and WD floppy controller chip are socketed in my unit. There were no visible signs of life on the WD control pins. Dumped the EPROM and verified its contents (they were good). Since the WD controller was socketed and I had a spare, I swapped it out. No joy there. At this point, lacking any other diagnostic information I decided to monitor the CPU's Address and Data lines to see if I could work out what it was trying and failing to do at powerup. Thanks to a new 40-pin DIP clip (thanks again, Ian!) it was pretty easy to connect up my logic analyzer (a Tek 1241 for those curious) and it pretty quickly became clear that while the CPU was running, it wasn't functioning properly at all. No matter how I looked at the address & data I couldn't work how it could possibly be running a valid program. Data matched up to the addresses being read (for addresses within the EPROM's address range anyway) but the ordering of the addresses did not seem to correspond to a running program. I desoldered the 6502 and stuck it in a working Apple II, and sure enough the Apple would not run with the 1581's CPU. I installed a replacement 6502 in the 1581 and I'm happy to report that it now works properly again! I believe this is the first time I've run into a faulty CPU in a vintage computer (or peripheral). - Josh