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
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.
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
buses.
Indeed - reset looks good and pulling it low gives an audible
kick/buzz from one of the motors, just like at power-up. AFAICS the
processor's running and not halted or waiting, which would favour your
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.
Cheers,
--
Steve Maddison
http://www.cosam.org/