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Old 20th Nov 2019, 9:54 pm   #11
Zelandeth
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Join Date: Jun 2006
Location: Milton Keynes, Buckinghamshire, UK.
Posts: 931
Default Re: Sun Microcomputer II Motortester 1215

Now we're getting somewhere.

Removing two nuts allowed the whole front bezel to be removed, allowing unimpeded access to the card cage.

This allowed me to make the first surprise discovery - the CPU. I was expecting something 8-bit, probably a close relative to processors we were used to seeing in the 80s. What I was not expecting was a 16-bit chip. A National Semiconductor INS8900D. Clocking in at 2MHz it's hardly going to set the world alight, but even so a 16-bit CPU must have been quite a bold claim to stick in the marketing literature , especially keeping in mind that this machine has its roots in 1979.

Pulling the "CRT" board didn't reveal anything obviously amiss or obvious tarnish on the contacts. There were however several socketed ICs, so these were all removed and reseated. Surprised to see that among the ICs in sockets is a 555 timer...wonder if they've had issues with reliability there.

Pleasingly powering it back up after this resulted in a rock steady display, the issue with the display dropping out apparently having been resolved.

Granted, the self test has raised other things in need of attention, but that's not wholly unexpected. If I'd been abandoned in a shed since 2005 I'd probably be claiming that service is required!

Despite this, it does happily go into testing mode, and correctly displays data.

Issues we've got to deal with:

HC, CO, amps, volts and ohms testers all fail the self test. It's also claiming that the line voltage is low. Oh, and the temperature probe thinks it's sitting at 160C.

I did carefully clean the mirrors of the gas analyser as it was full of gunk in the hope that might spring back to life that simply, but no such luck.

First port of call will be to do the remove/reseat routine on socketed chips throughout the machine I think, and especially on the IO/Mux boards...then have another look and see where we are.

While I had the front panel off I took the opportunity to clean both it and the CRTs as they were filthy.

The display looks really quite special I think with the way it just "floats" in the huge expanse of smoked glass (well...polycarbonate or acrylic).
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