Yes : Why do you insist on doing it blind? Seriously I do not see how you cna troubleshoot any part of a classic computer without observing signals. The problem could be any one of a number of things (which I will come to in a moment), unless you start making measurements there is no real way to determine what is going on. Troubleshooting _should_ consist of knowing what the unit should be doing, determining (by measurement) what it is doing and working out what could cause the differences. At this point, do you know if the problem is the controller or the floppy drive? In the case of the latter, have you tried to format, write and read a scratch disk? If it will do that, it points to head alignment problems. If not, the fault could still be in the drive. I assume the disk is rotating but have you checked this? Do the heads move at all? If you start with the heads near the spindle do they restore to cylinder 0 when you try to boot from the disk? The problem might be a fault in the head or read amplifier -- even something as simple as a dirty head On the controller side, given it's a 2797, I'd try asserting the test input and seeing what the setup waveforms look like. This will detect a serious failure of the data separator part of the IC or associated components. At this stage don't adjust anything though. Does the CPU try to access the FDC chip (is CS/ being asserted)? Is there activity on the other bus lines (maybe a bus buffer has failed and there is no data bus at the FDC chip). Does the FDC ever assert DRQ or IRQ? Does the appropriate bit of the system respond? Are the floppy drive signals (in particular Read Data) getting to the chip? Without more information as to what it is actually doing I don't think you have a chance to logically troubleshoot this. -tony