Fixing a DEC Letterwriter (LA100)

Tony Duell ard at p850ug1.demon.co.uk
Sun Jun 15 22:08:14 CDT 2008


> >> Anyway - the original problem is gone. With the (half) new RAM I'm now
> >> getting what at least appears to be a proper fault indication on the
> >> LEDs: both DSR and POWER/FAULT are flashing. This combination isn't in
> >> the user manual so my guess is it's failing the POST. If any of the
> >
> > Maybe soemthing like 'RAM Error' :-)
> 
> That was my first guess too. Running the ROM through a simulator and
> forcing the RAM test to fail confirms it. The problem? I'd managed to

OK...

> gouge out a bit of track while removing the ICs - just so happens it
> was one of the very tracks connecting /all/ the RAM to the address
> bus, so checking for continuity between the sockets I'd soldered in
> didn't reveal the problem.
> 
> So I fixed that and robbed a couple more 2114s from another machine.
> So all RAM is replaced but, lo and behold, ONLINE and CSR are back
> with a vengeance. So I'm basically back to square one, although not

Ah, but you've confirmed that the processor is doing something, and that 
it's executing the firmware (at least partially). If not, then the RAM 
failure, (albeit a man-made one) would not have been detected. Surely 
that is a staep forward.


> >> > I seem to have dumps of 147E4 and 148E4 here...
> ...
> > I'll get them on my way to you...
> 
> Many thanks! You may also want to send them on to Pete Turnbull for
> inclusion in his DEC ROM archive.

You are welcome to forward thenm on to him. I have no claim over them.

-tony



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