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Old 25th Oct 2022, 9:17 pm   #1
Realtime
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Question MK14 Rev VI PCBs

I’m wanting to build another Sloathie Rev VI MK14 but the supply of bare PCBs seem to have dried up. Coolsnaz2 is wanting to do the same, so I looked at what it would cost to buy a batch of V1.2 PCBs from JLCPCB in China. I’ve used them 5 times now and been very happy with the results.

The per unit cost including postage from China would be <£5 (depends on quantity and how the £ performs against the $). Add to this around £4.50 to distribute the boards by post in the UK. The preference is for a green or black solder resist with white silk screen. (Blue, red, purple and yellow resist is also an option). Turn-around is typically 10 days from placing the order, including delivery to the UK.

So, would anyone else be interested? It's a non-profit making offer - just need to make sure costs are covered. Aim to order in the next week or 2.

(I hope Sloathie is OK with that - it's his creation after all).
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Old 25th Oct 2022, 9:45 pm   #2
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Default Re: MK14 Rev VI PCBs

I ordered the very first batch of V1.2 PCBs (In black) from JLCPCB and the quality of those original five PCBs was excellent. One I used of course, the second went to Tim(bucus), the third to Philoupat over in France and the remaining two I sent to Slothie to use or sell, as he saw fit.

He built one of them up, it may be worth waiting to see if the remaining one is surplus to his current requirements.
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Old 25th Oct 2022, 10:36 pm   #3
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Default Re: MK14 Rev VI PCBs

How difficult is it to source the parts please to build a Mk14? I'll have a board if the answer isn't "not too difficult".

Ta.

Colin.
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Old 25th Oct 2022, 11:06 pm   #4
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Default Re: MK14 Rev VI PCBs

Most are fairly easy - the base price of INS8060 CPUs has risen to around £35 now which makes it the most expensive and the AM9111 rams are upto £6 odd but the Slothie VI offers a cheaper alternative to be fitted with a solder link.

If you use an original bubble type display the 7408 (has to be the plain TTL for drive ability) can be difficult but, with a modern LED display the LS are fine.

The INS8154 is listed by a member here on ebay at the cheapest you will find one so buy it now as they are rare as anything - I think Chris also has it on his site with his excellent PCB.

The 80L95 is a bit hard but you can use the 74 equivalent - I have also used the 80C95 without issue.
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Old 25th Oct 2022, 11:15 pm   #5
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Default Re: MK14 Rev VI PCBs

The 'hardest' parts to source are:

The INS8154 RAM/IO chip, which is optional but useful.

The 2111 RAMS (at least one pair, ideally two pairs, required). The AMD AM9111 is a suitable substitute.

The INS8060 (SC/MP) microprocessor.

Then there are the PROMs (one pair) - the original devices are National Semiconductor DM74S571(A), pin compatible devices are AMD AM27S13(A) and Philips / Signetics N82S131(A). There are also Tesla MH74S571 but, while they are quite widely available, it is not so easy to find anyone who can programme them. There is at least one auction site seller who sells programmed pairs of MH74S571 PROMs for the MK14 and at least two individuals here on the forum who can programme them. I can't programme the Tesla MH74S571 but I have a small stock of N82S131N and I would be happy to move them on to friendly homes, programmed, for what I paid for them. (Not a huge amount: I bought them before the price of everything went haywire).

Coming up close behind is the display which can be culled from a late 1970s calculator like the TEXET 880 or just bought as a NOS item, although they tend to come from eastern Europe.

For some of the items above the chances are that some forum members who have already built replicas bought more than enough of some of the parts needed, and may have some surplus to requirements.

What I would say is - be aware of what the MK14 actually is - a very basic microprocessor trainer with a hex keypad and a 7-segment display for output. It is a very big step down from a PET. When fitted with the RAM / IO chip it has 16 lines which can be used as input or output, making it a sort of retro-Arduino - except that when you switch it off, it forgets everything, hence the proliferation of MK14 fast loading projects which you will find scattered around in this forum subsection.

Last edited by SiriusHardware; 25th Oct 2022 at 11:21 pm.
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Old 25th Oct 2022, 11:18 pm   #6
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Default Re: MK14 Rev VI PCBs

Quote:
The 80L95 is a bit hard but you can use the 74 equivalent
..Which would be the 74LS365. As Tim points out some of the chips are 'original' TTL (not LS) and they have to be for correct functioning of the circuit under all forseeable circumstances. Tim mentioned the 7408 (two required) but there is also the 7445 as well.
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Old 26th Oct 2022, 9:59 am   #7
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Default Re: MK14 Rev VI PCBs

We should also say that the real thing still turns up on auction sites from time to time, but they are very expensive and if you actually plan to play with it then it is not really worth considering anything earlier than an issue V, the final version which Science of Cambridge made (which is of course why Slothie's PCB is designated the 'issue VI').

The issue VI PCB has a couple of unique features not found on any other original or replica MK14 PCB, the most important of which is that the system address, data and control signals are tracked to the rear edge connector making it much easier to connect peripherals like homebrew memory expansions, the original or replica SOC VDU, Karen Orton's 'Ortonview', Realtime's new CPLD based VDU and other odds and ends - Midi interfaces - Alphanumeric LCD displays, etc, to the machine.
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Old 27th Oct 2022, 6:53 pm   #8
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Default Re: MK14 Rev VI PCBs

I still have three blank issue vi boards in blue, but shipping from Canada is probably more expensive than buying another set from jlcpcb. I also have all the dificult to source parts.

I have 10 bubble displays from eastern europe though at least one of those has a couple of weak segments. The issue vi is a good electrical replica for experimenting, but probably not vissually accurate, so its probably best to use an adapter for 2x4 digit displays or 3x3 digit displays if you want to wire up the ninth digit.

I was able to get 12 82s131 proms, last stock from a supplier on utsource which seem to be blank, but I haven’t tried to build a programmer yet.

I’ve had more problems with sourcing ram chips than the rest of the parts. First order from utsource was good, second set was less than 50% yield. I did get a batch from ABRA electronics that were good, but they no longer stock the 2111/9111.

The reset button is slightly unussual, but easy to fit a 6x6 mm tactile switch with two legs removed.
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Old 27th Oct 2022, 7:19 pm   #9
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Default Re: MK14 Rev VI PCBs

I see a UK seller (who I have bought from before) with stock of IM6561s, the alternative RAMs which the issue VI (only) allows for, at about £8 each just now. Not super cheap, but not the eye watering amount currently being asked for one 2111 or 9111.

The only drawback with the 6561 type of RAM is that it is incompatible with the original VDU and Czech replica SOC VDU due to the fact that those units hold the read signal low while they read a whole line of screen data. Ortonview works fine with the IM6561s, as should Realtime's "Realview" (as we are currently calling it). If you map extra RAM at 0200-07FF and point an original or replica SOC VDU at that memory instead of the onboard memory that will also work even if the onboard RAMs are IM6561s.
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Old 27th Oct 2022, 7:27 pm   #10
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Default Re: MK14 Rev VI PCBs

Oh - Just found IM65X61 from another UK seller that I have bought these exact devices from before - they are being sold in lots of 10 - awkward - but for a mere £1.80 per chip. Probably the best current price for RAM which will run in an issue VI right now.
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Old 27th Oct 2022, 9:02 pm   #11
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Default Re: MK14 Rev VI PCBs

That seems to have sparked a longer good conversation, and I'd like one of the PCBs please.

Colin.


Quote:
Originally Posted by Realtime View Post
I’m wanting to build another Sloathie Rev VI MK14 but the supply of bare PCBs seem to have dried up. Coolsnaz2 is wanting to do the same, so I looked at what it would cost to buy a batch of V1.2 PCBs from JLCPCB in China. I’ve used them 5 times now and been very happy with the results.

The per unit cost including postage from China would be <£5 (depends on quantity and how the £ performs against the $). Add to this around £4.50 to distribute the boards by post in the UK. The preference is for a green or black solder resist with white silk screen. (Blue, red, purple and yellow resist is also an option). Turn-around is typically 10 days from placing the order, including delivery to the UK.

So, would anyone else be interested? It's a non-profit making offer - just need to make sure costs are covered. Aim to order in the next week or 2.

(I hope Sloathie is OK with that - it's his creation after all).
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Old 27th Oct 2022, 9:49 pm   #12
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Default Re: MK14 Rev VI PCBs

Very well...

The first attached image shows what an unpopulated black board looks like, the second shows the same PCB mostly built up side by side with my original Science of Cambridge issue II (with non-original, i.e., usable, keypad). When the photo was taken the issue VI didn't yet have its keypad tact switches fitted. I think the suggestion from Realtime was to have the new batch made in either green or black.

Although there are some differences especially in respect of the keypad key spacing, the similarity is amazing considering that Slothie never had an original MK14 to look at or take measurements from. As it turned out, the issue VI is about 5mm wider and 5mm longer than an original PCB.

Technically speaking the main difference is one extra IC, this was needed to support the use of either the original 2111/9111 RAMs or the alternative IM65x61 types. Given the price and scarcity of 2111/9111 RAM at the moment, that has proved to be a good decision by Slothie although at the time AM9111s were still available and reasonably priced.
Attached Thumbnails
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Old 28th Oct 2022, 1:03 pm   #13
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Default Re: MK14 Rev VI PCBs

Quote:
Originally Posted by SiriusHardware View Post
Ortonview works fine with the IM6561s, as should Realtime's "Realview" (as we are currently calling it)..
I can confirm that Realview (I do like that name even if it’s been used before) works fine with synchronous RAM like the 6561. it pulses the nRDS line for every memory access on a video line.
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Old 29th Oct 2022, 12:27 pm   #14
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Default Re: MK14 Rev VI PCBs

I'm looking forward to this.

I don't suppose anyone has a BoM I can use to start buying the necessary?

Colin.
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Old 29th Oct 2022, 2:03 pm   #15
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Default Re: MK14 Rev VI PCBs

The VI needs one extra chip which I can't remember but, the MK14 manual contains:

Click image for larger version

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ID:	267087
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Old 29th Oct 2022, 2:19 pm   #16
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Default Re: MK14 Rev VI PCBs

Quote:
Originally Posted by Timbucus View Post
The VI needs one extra chip which I can't remember but, the MK14 manual contains:

Attachment 267087
The additional device is a 74LS20 to do the memory decoding mod.
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Old 29th Oct 2022, 2:48 pm   #17
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Default Re: MK14 Rev VI PCBs

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.

Last edited by SiriusHardware; 29th Oct 2022 at 2:55 pm.
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Old 30th Oct 2022, 11:02 am   #18
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Default Re: MK14 Rev VI PCBs

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.
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Old 30th Oct 2022, 3:57 pm   #19
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Default Re: MK14 Rev VI PCBs

When trying to source older 74 series its sometimes also worth searching for the 54 series.

Did anyone order a set of boards?
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Old 30th Oct 2022, 4:26 pm   #20
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Default Re: MK14 Rev VI PCBs

Quote:
Originally Posted by Mark1960 View Post

Did anyone order a set of boards?
I'm ordering next week (probably tomorrow). Was just waiting to see if anyone else was interested. 3 so far including myself. Did you want one, or more?
Looks like postage to Canada would be around £11 (up to 750g, tracked)

Last edited by Realtime; 30th Oct 2022 at 4:32 pm. Reason: More info
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