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Old 27th Nov 2018, 4:57 pm   #117
Join Date: Apr 2018
Location: Newbury, Berkshire, UK.
Posts: 313
Default Re: MK14 schematic revisions

An interesting (hopefully!) postscript to this story regards SC/MP chips from China. I've seen them on eBay for ~6 which was suspiciously cheap. In april I ordered 5 chips for 26 because I thought it was worth the risk - I already had a SC/MP I'd bought from someone in Spain a year earlier which was quite old (aka "period") but I wanted a backup and thought that it was worth the risk of them being fake. time rolled on and eventually they arrived and I was slightly dissapointed that they didn't look right, they just has a curly N logo and "INS8060N" printed on them, with some kind of date code or serial number on the underside that didn't make sense. The one from spain had the white bar and the "ISP-8A/600" marking for a SC/MP 2 that I expected to see.

When I finished assembling the MK14 and it didn't work I initially thought it was a faulty SC/MP so I ordered another 2 from a different chinese seller who pictured chips with the "correct" markings, which I thought was a better bet. While I waited for the chips to arrived I actually determined I had a fault on the PCB which when corrected made the computer burst into life!

A week or two later I tried one of my batch of 5 Chinese SC/MP chips and it didn't work, so I chucked them all in a parts box and forgot them. Some time later the 2 new Chinese SC/MP chips arrived and I was dismayed to see they were not marked like my Spanish chip but like the other 5 Chinese chips.... not expecting much I put one of them in my MK14 and ..... it worked! Slightly bemused, I tried all the chips and all but one (the one I originally tested) worked too!

So now I have 6 processor chips that appear to work, plus the Spanish one thats in the MK14. They could, of course, be marginal chips that perhaps fail when pushed, although at the MK14's 4.33Mhz clock they're already "overclocked", or perhaps have faulty instructions that the MK14 PROM doesn't use - I haven;t tried it extensively, I just stepped them through the monitor ROM and tried modifying ram - but looking at them carefully some of them have obvious solder on the leads so they could be pulled from equipment and perfectly good. I wouldn't trust them to pilot a jet but they look like they'll be OK for hobbyist activities.

I can't say all the Chinese SC/MP chips are good, but I can say that it might be worth a punt, especially since "reputable" sources like part factors have them for 25 - 30 each, which is a little steep for most hobbyists.
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