MK14 Rev VI PCBs

[Mark1960]

I have a few spare boards but I think its cheaper for you to get from jlcpcb than ship from canada to uk.

I can probably supply 8060 and 8154 as socket pulls in good condition. If there is anyone trying to source these for their boards, then I’ll put a few sets in the parts offered section.

[ScottishColin]

My Stag doesn't seem to support any of those EPROMs, so I guess I'll source them already programmed.

Colin.

Originally Posted by SiriusHardware

The PCB has the IC type numbers helpfully screen printed on it, so for the ICs

INS8060 (SC/MP II microprocessor) x 1

INS8154 (RAM / IO x 1) (optional) x1

P2111 or AM9111 or IM6561 or IM65X61 (RAM). x2 or x 4.

PROMs: A blank, unused pair of any of the following:-

DM74S571 or DM74S571A (National Semiconductor)
or
AM27S13 or AM27S13A (AMD)
or
N82S131N or N82S131AN (Philips / Signetics)
or
MH74S571 (Tesla)

Before ordering any of the above PROMs check whether you can programme them yourself. if not then it is probably easiest to buy a pair which are already programmed with the MK14 OS (Version 2).

Logic ICs:
74LS00 x1
74LS04 x1
74LS08 x1
74LS73 x1
7408 x2
7445 x1
74LS157 x 2
74LS20 x 1
80L95 -or- 74LS365 x1

Of the logic ICs, the most 'difficult' ones may be the 7408 ICs, it is possible that one of our fellow forum members may have a pair looking for a new home. The ICs supplied in the original kits were usually National semiconductor (DM..... prefix) parts but I have found that Texas Instruments (SN..... prefix) parts usually work well in these as well.

Sockets for the above, you probably have 14 and 16 pin already but you will need some 18-pin sockets as well.

Voltage regulator: 7805 (MC7805, UA7805, LM7805, etc)

Crystal 4.00MHz (best for use with VDU) or Crystal 4.433619MHz (best match for programs in the owner's manual which use software timing).

I'm away from base at the moment - I will rustle up a list of the resistors and capacitors when I get back there, if somebody doesn't beat me to it.

Edit: I see Tim posted the original parts list. In addition to those parts there are also positions on the issue VI PCB for 14 x 0.1uF disc ceramic capacitors which go across the supply lines for the ICs. The original PCBs only had provision for about two of these but that wasn't very good practice.

[ScottishColin]

I will be when you get to them.

Thanks.

Colin.

Originally Posted by Mark1960

I have a few spare boards but I think its cheaper for you to get from jlcpcb than ship from canada to uk.

I can probably supply 8060 and 8154 as socket pulls in good condition. If there is anyone trying to source these for their boards, then I’ll put a few sets in the parts offered section.

[Phil__G]

Originally Posted by Timbucus

The 7408 are available at a bit of a premium from Silicon Ark but not the Nat Semi ones any longer only TI and Fairchild.

Any help? No idea who sourced RS:

[SiriusHardware]

My Stag doesn't seem to support any of those EPROMs, so I guess I'll source them already programmed.

They are actually bipolar fusible-link PROMs and if programmers can 'do' them they often have them listed under a different section from EPROMs, possibly 'BPROMs'. Only the really high end programmers from the 80s and 90s tended to support them because they were already old / obsolete even then. Today, there are only about three or four current commercially made programmers which can program BPROMs including the Tesla ones and they are probably all differently badged versions of the same unit - cost about £800-£900.

If you really can't programme them then you need to find someone selling some already programmed PROMs, for example:

http://jmprecision.co.uk/shopping/pg...&=SID#MOREINFO

That's not a bad price for two programmed PROMs which will no doubt be tested before dispatch as well since the same seller sells his own design replica MK14 PCBs.

If you feel lucky and think you can find any of the below three types cheaper yourself you can send them to me for programming, but be careful not to get suckered into buying the Tesla brand MH74S571s which are often misleadingly described / labelled as 'Generic' 74S571s because sellers know very well that very few people can programme those.

DM74S571 or DM74S571A (National Semiconductor)
or
AM27S13 or AM27S13A (AMD)
or
N82S131N or N82S131AN (Philips / Signetics)

Or, as mentioned earlier I have a small stock of blank N82S131N which I bought for a decent price and I'd be happy to let a pair of those go to a good home, programmed, for what I paid for them. There may be others here who are in a position to make you a similar or better offer.

[SiriusHardware]

If there is anyone trying to source these for their boards, then I’ll put a few sets in the parts offered section.

Mark, I'm not sure if it wouldn't be better for you to negotiate via PM, maybe one of the interested parties (if there is more than one) can act as broker and import and distribute the required parts on behalf of everyone who wants some - if you put them in the general 'offered' bit they could end up being bought by someone who doesn't even mean to build an MK14 and just hopes their value will continue to go up.

There is no forum rule against trading items and negotiating prices via PM. Where items are offered in the open forum, then the rules state the price must be fixed.

[SiriusHardware]

Oh, just to add - Colin, if you order the PROMs from J M Precision make sure they have the new/revised OS as that version is much nicer to use. The ad doesn't state which version of the OS they are programmed with but I would be surprised if they are not the 'new' version.

The 'new' OS also contains some useful firmware such as the routines needed to run the cassette interface (which is quite straightforward to build on veroboard). In the original version of the OS you had to type some code in before you could use the tape interface!

[SiriusHardware]

Also for Colin, if you want to read the user manual here is an online copy of the MK14 user manual which describes the operation of the unit for MK14s fitted with the 'new' OS.

https://www.heinpragt.com/download1/...20version).pdf

However that particular PDF version, widely available online, has page 88 (part of the 'Moon Landing' game listing) missing - Tim has a PDF with the missing page put back in - I have an offline copy of that corrected version but maybe Tim can point to an online copy.

[Mark1960]

Originally Posted by Phil__G

Any help? No idea who sourced RS:

I don’t know who RS sourced these from, they used to do the same with a lot of components, marking them with RS part numbers and removing manufacturers markings. That was one reason we always preferred Farnell for small quantities, especially for connectors where quality could be so dependent on the source.

I don’t think the manufacturer will matter for the 7408, so long as they are standard ttl and not ls, then its only a cosmetic issue trying to use nat semi for everything.

Some other parts can use 74hct if you are not concerned about testing compatibility of add on circuits. I’ll make a list of the substitutions I made on my second board.

[SiriusHardware]

I'm sure those RS 7408s from Phil would be worth a try, as I think he has a machine he could try them in. It might be useful to know how many complete sets of parts people are looking for - Colin is obviously starting from nothing but Cs2 and Realtime may already have quite a few of the required parts as this would not be their first MK14 build.

[Timbucus]

Originally Posted by SiriusHardware

Also for Colin, if you want to read the user manual here is an online copy of the MK14 user manual which describes the operation of the unit for MK14s fitted with the 'new' OS.

https://www.heinpragt.com/download1/...20version).pdf

However that particular PDF version, widely available online, has page 88 (part of the 'Moon Landing' game listing) missing - Tim has a PDF with the missing page put back in - I have an offline copy of that corrected version but maybe Tim can point to an online copy.

I have it hosted on my Google Drive https://drive.google.com/file/d/1UvE...usp=share_link

[ScottishColin]

Downloaded both PDFs - thanks very much.

Colin.

[SiriusHardware]

its only a cosmetic issue trying to use nat semi for everything.

In the case of the issue VI, I agree the main thing is to make it operational.

If I were building one of Martin L's Czech replicas I would strive very hard to make it look as original as possible with all National Semiconductor parts where possible.

That said, not all of the original parts in my issue II are Nat Semi, the RAMs are NEC uPD2111s and I think a couple of the 74 series are SN (Texas) parts rather than Nat Semi - I have never had to replace any of the ICs in it (touch wood) so all the chips in it are original SOC supplied parts apart from the INS8154 which was bought a few weeks later from Tandy.

What can be an issue is that the MK14 is reportedly a bit fussy about the pedigree of some of the chips, and here I am thinking mainly of the 74LS157s which TonyDuell mentioned can be a potential source of trouble.

For the record, these are the ICs used in specific positions in my issue VI.

7408s - Texas SN7408

74LS157 - National Semiconductor DM74LS157N

7445 - National Semiconductor DM7445N.

2111 - AMD AM9111DPC P2111A-2

What does everyone else have in these IC positions?

[SiriusHardware]

Downloaded both PDFs

The one I linked to is incomplete so you would be best off deleting that one and keeping the one from Tim's stash, as that one is complete, no missing pages.

Unlike later Sinclair manuals which were generally regarded as quite good, the MK14 manual is regarded by many as a poor starting point for a complete beginner which of course we all were in those days, as the MK14 was very likely the first programmable device of any sort that we had ever encountered.

I seem to remember that you (Colin) did say you had some distant past experience with assembly language in one dialect or another, though I can't remember what.

[ScottishColin]

My experience was mainframe assembler and was a looooong time ago, so I'm best regarded as starting from scratch.

Colin.

[SiriusHardware]

Well, the difference is that back in the day we were all thrown into it completely on our own with just the user manual to make sense of it all, whereas nowadays... you have us! (For better or for worse...!).

[Realtime]

[QUOTE=SiriusHardware;1509895]

What does everyone else have in these IC positions?

My Rev VI has:

7408s - Nat Semi DM78S08 (high-speed Schottky series. High current drive capability but the bubble display is normal brightness)
74LS157 - Texas SN74LS157N
7445 - 7445PC (no manufacturer's marking, but probably Fairchild).
2111 - Harris M1-6561B-9

and just for info, I'm using AM27S185 PROMS. These are 2K*4bit with the extra address lines tied to GND. So whilst not authentic, it was a cheap way of getting the board up and running. You'll see from the photo that the extra pins are overhanging the IC socket. I do now have some 27S13A's but haven't gotten round to replacing them. I'll use them on the new build.

[SiriusHardware]

I suppose you could make an asset of that arrangement if you added one or two movable links to force the state of the highest address bits either high or low and use that to select either the original or 'new' OS. Not that I am advocating the use of the original OS which I'm not very fond of, but some original MK14s still have it so it is useful to be able to check that any new hardware works with systems running either version of the OS. You could also put custom single-task firmware in one of the three currently vacant slots in the unlikely event that you can come up with a dedicated job which you'd like the MK14 to do which wouldn't be more conveniently served by an Arduino.

Generally speaking the OS version shouldn't have any impact on external hardware but the 'new' OS does tie up Sense-A, whereas the original version did not.

Looking around recently I find that of the pin-compatible PROMs which are 'easy' to program or get programmed, the AMD N82S131N tends to be the cheapest: About £5 each from a UK supplier at the moment, for example. The ones I have didn't cost that much, but I bought them about 2-3 years ago.

Several years ago, it was still possible to buy original DM74S571s for about that price, but no more.

[Mark1960]

My original issue IV has all nat semi 74 series, AM91111BPC same as it had originally but replaced original faulty parts, only one pair fitted as the extra pair was never fitted. Proms are original DM74S571, original large size 4.433618 MHz crysral, nat semi 9 digit bubble display. The 74ls157 are actually the DM74LS157J so ceramic dip, probably just whatever was available when the kip was produced. The IC sockets are RS branded, the old standard profile rather than low profile, I think the contacts are gold plated, this is why I haven’t expanded the ram as I haven’t been able to find matching sockets. I avoid messing with this original now as the sockets are becoming a bit intermittent due to swapping chips for testing spares.

I have two issueVI, second was built with pin headers for 8060, 8154, base ram and proms, then I can fit ZIF connectors to test those components. This board has 82s131 proms, both sets AM9111 rams, DM74LS365, motorola SN74LS157, DM5408J ceramic, DM7445N, and a mix of suppliers of the remaining 74ls parts. Display is 9 digit bubble type but not sure of the manufacturer. Crystal is low profile 4.433618 MHz.

The first issue VI was robbed of its parts to complete the zif connector test board. Now has TI 74AHCT08N, phillips 74HCT00N, TI 74AHCT04, CD74HCT20N, phillips 74HCT173N, nat semi DM7445N, TI SN74AHCT08N, TI SN74HCT157N, phillips 74HCT365N. Using a 3x3 digit display, 0.28”. AM9111DPC ram, and no proms, running this with a daughter board and IS61C1024 ram, with battery backup providing the low 2k of every 4k block.

Edit to add this issue VI is running an 8 MHz low profile crystal in a socket so it can be easily swapped.

Edit, I should also mention that the 3x3 digit display has 500 ohm series resistors for each segment to limit the current due to using 74AHCT08 drivers. Not sure if something would give out smoke if these were not included, also suspect the display would be too bright for comfort.

[coolsnaz2]

I ordered a complete set of chips, except roms from LittleDiode in May 2022. Some of the chips are more expensive than Ebay, but at the time is was convenient for me to purchase all from one retailer.

The most difficult item to find was the 8 Digit 7 Segment display, which was eventually found on Ebay for £25, and the display didn't come with a ribbon cable. I also purchase 8 Digit 7 Segment Module MAX7219 from Amazon, 4 for £10, see attached photos. While I appreciate the display is not original or authentic I find the display completely satisfactory for the replica board.

The second most difficult item was the reset switch, which was eventually found on AliExpress, but took almost 2 months to arrive. I bought 10 of the black version, so I have a few spares.