Troubleshooting an IBM 5155 - (portable personal computer)

Not on-line, but at least I have a schematic. It doesn't look very complicated either. The alignment adjustments, in general, are what are known as 'interchangeability adjustments'. In other words, if they're a bit off, the drive will be able to format, read, and write its own disks, but those disks will not be useable on other drives, and vice versa. So what you do first is to hook the drive up as B: and try formatting a blank disk in it. Note that if, for some reason, the machine thinks it only has one drive, it'll map A: _and_ B: to that drive. You'll get some obvious messages if this has happened, in which case the problem is certainly not just alignment. If the problem is more than alignment, then you need a 'scope, logic probe or logic analyser. A drive exerciser is fun too, but by no means essential as you cna talk to the PC's disk controller card and get it to, e.g. start the spindle motor and move the heads around. What I'd do first is start the motor with a scratch disk in the drive and check you get pulses (at 5 Hz) on the index/ line. Then I'd try stepping the head in and out, and see if the track0 sensor line changes correctly. After that you'll probably delving into the read/write amplifiers... This sounds like track0 sensor problems. I assume you've blown the dust out of the sensor? If you have a multimeter and logic probe, I'll dig out the schematic and tell you what to look for. -tony