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Old 8th Nov 2020, 11:30 pm   #88
Buzby123
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Join Date: Oct 2011
Location: Culcheth, Cheshire, UK.
Posts: 637
Default Re: I found it! A very sorry looking MK14.

Well, I've spent the last few hours checking the address decoding.

I removed ROMs, RAMs, and CPU. Put wires from a breadboard micro to drive A11-A8 and WDS/RDS.

Wrote code to wiggle pins cyclicly at a few hundred Hz, and prodded my scope where the decodes should come out. They all looked OK. ( I didn't actually check the addresses, just that the CE pins wiggled up and down nicely. )

So it looks like ROMs and/or ROMs are faulty. I've got four 2111s, and swapping them in all combinations made no difference at all. Using 'old' ROMs gives a different wrong display.

Tomorrow I'll rig up a RAM tester, and a ROM dumper.

I'm assuming those of you with VI boards just plugged all the bits in and it worked straight off ?.

Cheers,

Buzby
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