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Old 10th Oct 2018, 9:52 pm   #25
julie_m
Dekatron
 
Join Date: May 2008
Location: Derby, UK.
Posts: 7,226
Default Re: 486 PC. Keyboard problem.

It certainly sounds like a motherboard fault. The BIOS will try to measure the amount of RAM during a full-length power-on self test, by determining the first location that can't be read back after writing to it. A loose connection on an expansion card or SIMM, or a dodgy decoupling capacitor, could certainly cause unreliability. Is the processor in a quick-release socket?

If the CNC machinery connects to the motherboard via expansion cards that plug into the old-fashioned 8- or 16-bit slots, then in the worst case it ought to be possible to replace the whole motherboard

Incidentally, my secondary school had in the CDT department a mini-CNC lathe controlled by a BBC Master 128. Very sophisticated for c.1987! It was most often used for making threaded inserts for lampholders.
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