6 Apr
2011
6 Apr
'11
5:02 p.m.
Interesting. This sounds liek a stock fault with these
Lisa drives, I
think Terry had much the same problem.
Yes, exactly the same problem and in fact in two of the three drives I had.
It does sound now like a common Lisa floppy drive issue.
Just to recap, in both these drives I replaced the TA7259s with new ones
plus the capacitors on the outputs as Tony suggested. No change whatsoever.
I also checked waveforms of the hall effect devices on the two drives. The
waveforms on all hall-devices looked very consistant both within a drive and
between the two faulty drives. In saying that, the pattern of the wave was
the same the amptitude between devices within a drive varied. From memory
device C had about 2/3 the amptitude of device A with the amptitude of
device B smack in the middle between these two (or maybe C was the larger
and A was the smaller...I'll need to consult my notebook).
This was the same for the other drive.
Had I seen the lesser amptitude on device C but A and B were the same I
would have thought it strange. However B was in between the two so I
figured this gradation in signal strength between the hall-devices was
suppose to be like that. On both drives and it was entirely consistant in
the size and distribution of the amptitude between A, B and C.
What I didn't do was compare these scope readings with a normal drive. None
of those hall-device readings looked obviously faulty though.
Given this fault doesn't appear to be a one-off, but may be common with
aging Lisa drives it would be good to get to the bottom of it. It may need
someone with more diagnostic skills and understanding than me though.
Terry