Troubleshooting an IBM 5155 - (portable personal computer)

[Kelly Leavitt]

> 
> > The heads are selected by U4 (75451 dual AND gate/driver), 
> > the outputs of 
> > which are pulled to+5V, and slo drive the bases of Q7 (Head 
> 1) and Q6 
> > (Head 0), PN2222 transistors via restors. One input of each 
> > of the AND 
> > gates comes from the power-OK circuit, built round Q9 and Q10 
> > (as this is 
> > common to both heads, it's working correctly), the other 
> > input comes from 
> > the sides select signal on the connector (U4b, for head 1) or 
> > from that 
> > signal inverted by U8b (7414) on U4a, for head 0. That should 
> > give you 
> > some components to check.
> > 
> Are you sure U4a drives Q6 and U4b drives Q7? Tracing the 
> board shows them
> on Q7 and Q8. Yikes. Any chance you could scan the schematic 
> and email it?
> 1bpp tiff, bmp or pcx would do. The higher the resoultion the 
> better, but I
> could probably make due at 150dpi.
> 
> You could even send it in seperate parts. I could then stitch 
> them together.
> Making some preliminary measurements, it's beginning to look 
> like a head
> problem. I am reluctant to actually load the heads until I 
> have to. I still
> have not "cleaned" the top head thouroughly, although it seems clean
> examining it through a loop.
> 
> I may just install a pair of known good drives in the machine and
> troubleshoot these two independantly. At least I would have 
> matching drives
> in the machine until I can figure out what is wrong here.
> 
> Thanks,
> Kelly
> 

I don't kwow what it means when I reply to my own replies, but here goes. I
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.

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. 

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?

I'm going to bed now. More tomorrow.

Kelly