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Old 27th Mar 2021, 3:15 pm   #265
ortek_service
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Default Re: I found it! A very sorry looking MK14.

Quote:
Originally Posted by Buzby123 View Post
And there's more !

Today I found in the attic a box with about 30 databooks that I've not seen for years. One of them I think is the same NatSemi Memory Data as linked to a couple of posts ago.

I just had a quick look in it, and page 11-82 looks very interesting.

We MK14 owners know two things. (1) SoC cut every corner possible, (2) the PROMs get @***ing HOT !.

It looks like NatSemi had this heating in mind, and suggested a way to reduce it dramatically. That's what's on page 11-82.

Have any of you seen these PROMs in commercial products, did they get this hot in those applications ?

That's interesting App Note info info, I'd not noticed before - Especially as it was missing from the very abridged 20pgs pdf I'd previously got with the TTL/Bipolar PROM's programming procedure page and just the contents pages (minus the last one, listing the App Notes), and the cross-reference pages.

This 1977 databook 74S571 datasheet on pgs 5-13 to 5-17 also covers the 74S570 Open-Collector version, - as well as seemingly duplicating the Programming procedure for these on page 5-1.
It seems the 4 pages (3-16 to 3-19) later date unknown? one, I'd previously linked to was complete, but that NS had removed the programming procedure duplication from it (so needed other pages from their memory databook), as well as removing details on the internal circuitry - but they had added an extra SM PLCC version, and also that Testability note you'd noticed. So useful to have a copy of both versions.

To be fair to SoC, I don't think it was they who'd cut corners regarding power consumption reduction, as I'd never seen anyone else doing that, but National Semiconductor themselves - As most memory devices have a Chip Select as well as an Output Enable, to save unnecessary power.
If a program was running entirely from RAM, then you could save quite a bit, but if the with the monitor in the PROM's running to update display & scan keys etc. then the PROM's would still be frequently accessed - albeit needing to be selected for rather less than 50% of the time.


But rather than trying to mod the original design to include power-saving, then adding heatsink(s) would probably be simplest to preserve the PROM's a bit, and efficiency is not too important if not left running all day. If D/S thermally-conductive adhesive tape was used, rather than thermally-conductive epoxy etc, then they could be later removed for originality.

Or a metal plate clamped over the PROM etc. IC's, with some thermally-conductive gap-filler silicone rubber sheet underneath (would be easier if they'd laid the board out with PROM's adjacent to each other like others did!) - Just need to make up a suitable non-conductive clamp system, to fit around PCB, without some convenient mounting holes for it.

This does allow you to revert it be just a museum piece / retain resale value, whilst actually being able to use it wit less worries of these IC's failing - Although I'm tempted to just substitute a plug-in EPROM adaptor assembly for the PROM's, and keep the originals safe.

It may also be worth seeing if the bit lower power AMD 27S13A or N82S131 that SiriusHardware has tried could be obtained at a fair price, and are easily-programmable by most 74S571 programmers / supported by some common universal ones.
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