Troubleshooting an IBM 5155 - (portable personal computer)

From: Kelly Leavitt <CCTalk_at_catcorner.org>
Date: Tue Jan 18 20:19:28 2005

> From: ard_at_p850ug1.demon.co.uk [mailto:ard_at_p850ug1.demon.co.uk]
> To: cctalk_at_classiccmp.org
>
> > I don't kwow what it means when I reply to my own replies,
> but here goes. I
>
> I do it all the time, but then I am know to be insane...
>
> > have the same continuity measurements on head 0 and head 1.
> > However, if I swap the controller board
> > the problem
> > stays with the drive.
>
> Ah, so it certainly looks like a head problem :-(
>
> >
> > So, if I have the same continuity, and the problem doesn't
> > seem to be on the
> > controller, I can only guess either dirty or magnetized
> > heads.
>
> Magnetized heads are not normally a problem with floppy
> drives, at least
> not as big a problem as dirty heads.
>
> It's a pity you don't have a 'scope. I'd ask you to connect it
> (differential inputs) to TP1A and TP1B, ground to TP2. Those are the
> outputs of the read preamplier part of U2 (3470). You could
> then compare
> the read signal from the 2 heads.

I'll see if anyone in the local radio club has any I could borrow for a few
evenings. I know how to use one, it's just been a few years. I have an old
Heathkit scope behind me, but there's another thing waiting for my
attention. The trace is about as wide as my pinky and as noisy as heck. Not
real helpful I'm afraid.

>
> >
> > Since I don't have access to a tape head demagnetizer (hey,
> > all I use is
> > DTRS for my recording), how else could I demagnetize these heads?
>
> Can you not still buy demagnetizers? There are plenty of magnetic
> recording heads still in use...
>
> But I would try really cleaning it first. It could be a speck of oxide
> stuck across the gap or something.

I stopped by the local pharmacy (chemist on your side of the pond I think).
I had to special order non-diluted alcohol. It should be hear tomorrow. Of
course I have to work late tomorrow, so my wife will pick it up. I think
Radio Shack still carries an inexpensive head demagnetizer. I'll check. It
will probably be special order too.

In the mean time, I put the original drive in there and one of the spare
DS/DD drives I had laying around (doesn't everyone on this list?). It is now
working with an A: and B: drive. Now I just need to do some cosmetic work
and this little machine will be in great shape.

What is the general opinion on adding an HD to this machine (if it will even
work)? I've got plenty of ST-406/ST-512 interface drives and controllers for
8 bit machines. Of course I only want this for show and tell, so it is not a
requirement.

Kelly
Received on Tue Jan 18 2005 - 20:19:28 GMT