Troubleshooting an IBM 5155 - (portable personal computer) - test-drb@ccmp.vtda.org

17 Jan 2005

...

  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