Fixing a DEC Letterwriter (LA100)
ard at p850ug1.demon.co.uk
Thu Jun 12 21:44:22 CDT 2008
> > I guess I'd start by checking all the PSU outputs. I doubt that's the
> > problem here, but PSU problems can cause the most amazing faults...
> That's indeed where I started and, according to the multimeter, all is
> OK. Could of course be something gruesome going on that I will only be
> able to detect when I take a scope to it...
> > I do have the printset, but it would take me a little time to find it. As
> > ever I have no scanenr, so I can't provide a copy.
> Don't worry - I have found the prints on Manx (they were "hiding" on a
> second page of search results that I managed to miss). For the
> archive: http://www.vt100.net/manx/details/1,4232
IIRC this unit is microprocessor-controlled 8085?) and the LEDs are under
the control of that microprocessor.
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.
Other than that, I guess you start by checking the processor clock and
reset signals, then see if there's any activity on the data and address
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