Finally fixed it! (was: Re: Complete success,

[Tony Duell]

> > Of course the system now still won't boot (I can hear the drive
> > head move, and then the RL02 FAULT light comes on) but it's likely
> > the OS/8 image got clobbered when the chip failed and the CPU
> > started writing to odd places.
> 
> Hmm... I don't think filesystem problems will cause the Fault light to
> light up, just problems within the drive.  You may need to trace back

Correct. Even a sector with incorrect checksum will not cause the FAULT 
light to some one, the checksumming is handled by the controller. 


> all of the causes that sum up to "Fault" to see what's going on.

The way I always trace FAULTs of this nature is to grab the RL02 printset 
and look at the  DDrive Logic PCB scheamtics. It's clear from that 
there's effectively a big OR gate that comines a lot of different signals 
to turn on the FAULT light. I run a logic probe over each in turn to see 
which is the one that's asserted, then trace back from that.

-tony