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Old 29th Jun 2015, 9:37 pm   #5
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: The Sinclair / Science of Cambridge MK14

Thanks for the info about the 'metal dome' upgrade - I have never seen one up close.

My knowledge(?) about the address and control lines being available on the rear edge on late marks comes from the VDU board 'manual', which states that the connections were available there on issue IV onwards. If you can lay hands on yours at some point it will be interesting to see what issue it is and what improvements that issue did or did not incorporate.

On earlier marks you just had to find the connections anywhere you could, typically on the tracks surrounding the CPU. It looked horrible.

If I were considering reconnecting it now I'd solder a 40 pin turned pin socket to the CPU socket pads on the UNDERSIDE of the PCB, then use a 40 - pin DIL header on some wide ribbon cable to pick up and convey all the required connections rearwards, beyond the rear edge of the MK14 PCB. Doing it that way, the whole VDU could be unhooked in a second or two. (Although, I suspect there may have been one or two required track cuts and mods to undo as well - not including the need to change the main crystal to 4.00Mhz when the VDU was fitted).

Yes... with the new monitor fitted you had to tie Sense-A to 0V either directly (in which case it was effectively lost to you as a user input) or with a resistor, say 1K.

I believe it was because the revised monitor also incorporated support routines for the 'Single Step' feature, but if you didn't add the little bit of hardware required to make that work, the pulldown resistor was needed to maintain normal system operation when the single-step hardware was absent.

I don't think even the MK14's most ardent fans would claim it was a great machine, but for someone on my budget (I was in my early teens) it made the difference between owning and programming a 'computer' or not owning one. Even then, it took me the best part of three months to save up half the cost, at which point my parents realised I was serious and donated the other half.
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