my Data General Nova 4/X, disk woes continue

[Tony Duell]

> I suspect the Read/Write Board. So I ordered modern monolithic
> replacements for the remaining old mono chips from Digikey, and
> shotgunned all the old electrolytics etc for good measure, in two
> places electrolytics replaced with tantalums (didn't have
> .82uF's).

I am never in favour of shotgun replacements. It's the brother of 
board-swapping in that you don't know what the fault was, you don't know 
you've found it, so you can't know it's fixed.

Now, you say you _susepct_ the read/write board. Do you have a good 
reason for this? You're getting random errors (so presumably it works 
sometimes, you can get this drive to read/write). It might be the 
read/write board. It might be the PSU. It might be the head position 
servo. Etc. IMHO you need to do a lot more tests.

> After warm-up, it's worse. Signals all through the path look

COuld this be a thermal problem? Have you tried heat/freezer on chips in 
the read chain and the servo?

> OK, hot and cold. I can see no difference, but this is 10 MHz
> NRZ data, in a two-state amp with AGC. I think I'm screwed.

Have you looked at the servo waveforms? Does this drive use the standard 
optical scale transduver? What do the outputs from that look like? What 
about the positioner drive signal?

-tony