TRS-80 Model 4 help requested

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Thu Feb 27 18:21:17 2003

> > From: ard_at_p850ug1.demon.co.uk (Tony Duell)
> >
> > Try re-seating the 'ribbon cable' between the CPU
> > board and the disk controller PCB _at both ends_. I
> > would estimate that over 50% or disk problems on
> > M3s and M4s come from this cable!
>
> You're right about this. It all starts to come back to
> me... *Grin!*
>
> This was one of the first things I'd do when a machine
> came in with disk controller problems.
>
> I'd also remove the cable totally and clean the
> connections with a pencil eraser and possibly some
> alcohol.

On my M3 (but not on the M4 yet) the cable got to such a state that I
removed it totally. I soldered a 20 pin SIL header to the CPU board and
used a 40 way IDC connector and cable to mate with it. I soldered every
other wire in the cable to the FDC board. Never had any more problems...

> But since the behavior changes when he moves the
> drives, it sounds like his "0:" drive is bad.

I rather gave up when he started swapping parts round!. I prefer to start
with a configuration that I know was capable of working...

As you said there are possible drive select and termination issues. So
I'd want to keep the drives as they were originally, at least for the
moment. And I would then start troubleshooting drive 0.

In particular, does it do anything when the machine is powered up/reset
with a disk in that drive. Does the motor even spin? If not, then I would
grab the logic probe and meter and start tracing signals. If you want to
do this, I have the schematics, etc to hand, and can talk you through it.

-tony
Received on Thu Feb 27 2003 - 18:21:17 GMT