Fixing a DEC Letterwriter (LA100)

[Steve Maddison]

2008/6/14 Tony Duell <ard at p850ug1.demon.co.uk>:
> I think the 2114 is the most unreliable chip I've ever seen. And it
> doesn't seem to be any particular manufactuer that's to blame either. I
> would certainly check these very carefully.

I whipped all the 2114s out today and popped in a set of IC sockets.
Thinking they couldn't possible /all/ be bad, I got two replacements,
and have experimented with different combinations of old and new. Very
scientific, I know ;-) I thought it was worth a try before hacking up
a test rig.

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
2114s were still working, I probably fried them getting them out. I
see if I can borrow a couple from a ZX81 or something else lying
around here.

> I seem to have dumps of 147E4 and 148E4 here...

Was just looking for those! I'd sure appreciate a copy if you could
mail them or somehow get them online. I might try my luck at tracing
through a bit of code to see which conditions are causing the light
show.

-- 
Steve Maddison
http://www.cosam.org/