PDP-12 Restoration at the RICM

[tony duell]

> We swapped the TU56 and TU55 drives between the PDP-12 and the PDP-8/I. We

Does the TU55 work correctly on the 8/I ? 

> The TU55 behaved a little better than the TU56, and sometimes would
> actually boot OS/8. We continued chasing the issue and found glitches on
> data channel 3. We have swapped every module and cable that relates to data

What exactly do you mean by 'glitches'? Are these on a TTL level signal, an analogue
output of the read amplifer, or what? 

Have you looked for glitches on the other data channels? 

> channel 3, but have not been able to fix the glitches. The glitches are
> there with both the TU55 and the TU56, so the problem is in the TC12
> controller.

IIRC this thing has 3 data channels, so is channel 3 on the outside of the head/tape?
Could it be some external interference that happens to be picked up most strongly
by that head winding?

-tony