Fixing a DEC Letterwriter (LA100)

Tony Duell ard at p850ug1.demon.co.uk
Fri Jun 13 20:42:29 CDT 2008


> 
> 2008/6/13 Tony Duell <ard at p850ug1.demon.co.uk>:
> > IIRC this unit is microprocessor-controlled 8085?) and the LEDs are under
> > the control of that microprocessor.
> 
> Absolutely correct. Everything between the processor and the LEDs in

You know, I can't rememebr the face of somebody I met yesterday, but I 
rarely forget a scheamtic. Even though (in this case) I've not worked on 
an LA100 for over 10 years...)

> question looks to be fine so I suspect the program just isn't running
> right.
> 
> > What does it use for RAM? If 2114s, then the lucky-dip side of me says to
> > check/replace them. I've had _dozens_ of that chip fail in all sorts of
> > devices, with various odd results.
> 
> Right again, and thanks for the tip.

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.


> RAM hunch. The stickers on the EPROMS' windows are a bit crusty too,
> and starting to shine through, so I'll add checking for bit rot to the
> list as a last resort.

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

-tony



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