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Old 8th Nov 2020, 11:02 pm   #89
SiriusHardware
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Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 7,513
Default Re: I found it! A very sorry looking MK14.

Yes, that was certainly my experience, I put the parts in and it 'just worked'. My board and Tim's both came from a single batch of 5 that I had made by uploading the unmodified project files from Slothie's post early on in the 'vdu' thread to JLCPCB.

It's impossible to know whether whoever had your board made carried out any changes but why would they when they know, from reading the relevant thread here, that the boards work exactly as designed. If you are spectacularly unlucky you could have an etch fault or some other manufacturing fault on your PCB.

To read out the PROMs, if you have an EPROM programmer make up a jig which places the two PROMs side by side as D0-D3 and D4-D7, commons up the A0-A8 pins, _CE pins and power pins on both ICs, maps them onto the matching pins on the footprint of a 2716 EPROM and drop the 'jig' into your EPROM programmer. On the programmer, choose 2716 and then limit the address range to 0000-01FF and read the contents out of the '2716'.

One other issue we have been made aware of somewhere in these threads, and this is not just relevant to the issue VI - some versions of 74LS157 don't work in the basic MK14, apparently even in original machines, so if those RS brand ICs you mentioned happen to include the 74LS157s then maybe try a pair of other-brand 74LS157s. I didn't bring this up before because it seemed you were using parts from a once working MK14 but since you seem to have several non-original parts in there this may be worth looking at.

Originally all the chips supplied in MK14 kits were National Semiconductor (DM or MM prefix) but a few other brands were eventually substituted for some of the chips - notably Texas (SN prefix).

In my issue VI I have a mixture of DM and SN prefix types, the 74LS157s are SN (Texas) types in mine.

Elsewhere in these threads there are posted Arduino Uno sketches for (a) reading out the contents of a 512-byte ROM and (b) doing basic functional tests on 2111 RAMs. If you don't already have a specific way to test the PROMS and RAM I'll try to track those posts down for you.

Last edited by SiriusHardware; 8th Nov 2020 at 11:08 pm.
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