Troubleshooting an IBM 5155 - (portable personal computer)

[Tony Duell]

> 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 (I know, Tony, you generally frown upon "swapping"
> for troubleshooting, but I couldn't find anything electrically), 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 magentized heads. I noticed
> that if I close the drive with no media and open it slowly, the heads stick
> together until there is a bit of load on them to pull apart. Kind of like
> the are lightly magnetized. 

Magnetised heads are not notmally 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.

> 
> Since I don't have access to a tape head demagnitizer (hey, all I use is
> DTRS for my recording), how else could I demagnetize these heads?

Can you not still buy demagnetisers? There are plenty of magnetic 
recording heads still in use...

But I would try really cleaning it firt. It could be a speck of oxide 
stuck across the gap or something.

-tony