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Old 7th Sep 2020, 11:08 am   #34
SiriusHardware
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Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 7,538
Default Re: I found it !. A very sorry looking MK14

Since your system obviously has extra RAM (over and above the standard full 640 bytes) you would have needed a hole somewhere in the memory map somewhere for that memory to drop into.

Only the final issue (Issue V) had that memory hole available as built. MK14 issues II to IV all had unwanted 'images' of the OS in the region 0200-07FF which first had to be removed before any new offboard memory could be mapped into that area, so some of that hackery on the underside of your MK14 PCB will be for that purpose.

In post #6 of this long running thread

https://www.vintage-radio.net/forum/...d.php?t=145663

there is an attached single page document which was sent to me by SOC (circa 1978) in response to my question to them about how to expand the memory.

The document doesn't actually describe how to add more memory, it describes the mods required to a specific revision of MK14 - possibly issue II - to remove the unwanted PROM images at 0200-07FF as a precursor to adding more memory.

Unfortunately the document describes the mods 'visually' (Cut this, link that) rather than at circuit diagram level, but if you look at yours and yours has those mods applied you can probably say those particular mods don't need to be undone in order to get the machine to work stand-alone with its onboard RAM, since all they should do is remove the unwanted PROM images.
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