Troubleshooting an IBM 5155 - (portable personal computer)

[Tony Duell]

> Well, I just went through the "closet-o-drives" and I don't have any other
> Qumes laying around. Furthermore, the DS/DD drives I do have the card edge
> connector on the wrong side. The included cable is not long enough to plug
> one of these in and leave the one working original drive. Does anyone have
> the service manual online for this drive? I would really like to get the

Not on-line, but at least I have a schematic. It doesn't look very 
complicated either.

> Qume drive working, but don't know where to go next. I guess I could swap
> the boards between the two units, but that'll only tell me if it is
> electronic or electro-mechanical. 
> 
> Other than that, any suggestions for figuring out if it is alignment, broken
> sensor, or something electrical? 

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...

> 
> Here is what's happening with this drive:
> The computer goes through it's mem-test, then advances the head. The head
> retracts, then the system immediately dumps to cassette basic. It doesn't
> even seek again.

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