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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 10th Nov 2020, 4:24 pm   #101
SiriusHardware
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Default Re: I found it! A very sorry looking MK14.

Can you try testing those ICs as type 7445 instead? Should work I think, the tester should just put pullups on the outputs. Just wondering if the TS200's test algorithm / truth table for 7442 is incorrect/faulty but the one for 7445 is OK?
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Old 10th Nov 2020, 7:04 pm   #102
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Default Re: I found it! A very sorry looking MK14.

Tried testing chips as 7442 and 7445, all test bad.

Lashed up a breadboard, inserted 7442, wiggled d0-d3, ten outputs changed as expected.

So from that we can deduce my TES200 is not as clever as it should be.

TES told me all the other TTL parts are OK, and I'm tempted to believe that, as when I scope the board all the pins I expected to wiggle are wiggling.

But still no nearer to getting Vicky running

The only chips not tested yet are RAMs and ROMs.

Cheers,

Buzby
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Old 11th Nov 2020, 1:10 am   #103
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Default Re: I found it! A very sorry looking MK14.

I've got dozens of vintage TTL chips, but not a single 7445 among them !.

Although I'm now fairly certain the problems lie in the ROMs or RAMs, I have one last check on the PCB.

I don't know the orignator of this VI board, but there is a number on the back which I think is a fab shop batch identifier.

The number is in tiny print, an inch below the 'S' of science. The number on my board is '2364469A-Y118-200602'. If this matches any known working VI them we know they came from the same production run, and mine should be OK.

A faulty PCB is a real long shot. All the points I've probed with a scope show good signal levels and shapes, and I even dug out my 308 logic analyser ( contemporary 1981 kit !) to see the what the data bus looked like for reads and writes. ( I must learn to use this bit of kit properly, I've had it long enough. )

If I don't get Vicky working, I won't get Micky working either.
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Old 11th Nov 2020, 9:22 am   #104
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Default Re: I found it! A very sorry looking MK14.

I'll look when I get home but I know that my board and Tim's came from a one-off batch of five which are all accounted for so yours is not one of them - ours are black, not green.

Whoever had yours made had their own batch of five or more independently made so the PCB manufacturer would have treated it as an entirely separate run with no relationship to our batch. There is no way for us to know whether whoever had yours made made alterations for some reason, although that would not have been a sensible thing for them to do given that the original batch work. Unfortunately you are the first other person that we are aware of who has tried to build one of these PCBs so we can't refer you to anyone else who has at this time.
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Old 11th Nov 2020, 9:50 am   #105
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Default Re: I found it! A very sorry looking MK14.

If your problem is ROMs, how unlucky are you to have at least one duff IC in both sets of PROMs? If RAM, how unlucky to have at least three faulty ones out of four? It would have taken some odd kind of catastrophe to wipe all of those out but leave the TTL untouched.

The SC/MP itself, I would imagine you can only really prove by substitution.
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Old 11th Nov 2020, 3:55 pm   #106
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Default Re: I found it! A very sorry looking MK14.

Quote:
Originally Posted by SiriusHardware View Post
... how unlucky are you to have at least one duff IC in both sets of PROMs? ...
Yes, that's the story of my life. The only luck I have is bad !.

I started to rig-up a ROM dumper, but then remembered that the MK14 rewires both busses, so I wasn't sure if I was going to get the same values back as expected. I am however going to test the RAMS, at least I know I should get out what I put in.

On order is a new set of TTL parts, so no doubt then about their provenence.

Cheers,

Buzby
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Old 11th Nov 2020, 5:13 pm   #107
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Default Re: I found it! A very sorry looking MK14.

Quote:
Originally Posted by Buzby123 View Post
Quote:
Originally Posted by SiriusHardware View Post
... how unlucky are you to have at least one duff IC in both sets of PROMs? ...
Yes, that's the story of my life. The only luck I have is bad !.

I started to rig-up a ROM dumper, but then remembered that the MK14 rewires both busses, so I wasn't sure if I was going to get the same values back as expected. I am however going to test the RAMS, at least I know I should get out what I put in.

On order is a new set of TTL parts, so no doubt then about their provenence.

Cheers,

Buzby
The MK14 only plays fast and loose with the address lines on the RAM. The ROM address and data lines are wired as specified on the chip.
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Old 11th Nov 2020, 5:29 pm   #108
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Default Re: I found it! A very sorry looking MK14.

If I can find time later today Iíll try running my MK14 with RAM removed, then maybe if you get the same symptoms with no RAM it might indicate your PROMs are ok.

Looking at the monitor code it might not show anything on the display with no RAM, the digit counter is held in RAM so I think should be 0F with no RAM fitted.
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Old 11th Nov 2020, 5:57 pm   #109
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Default Re: I found it! A very sorry looking MK14.

As Slothie says, although the wiring to the RAMs is scrambled - it was scrambled on the original machines and is scrambled on the issue VI - the wiring to the PROMs is exactly as per databooks so PROM D0 -is- DO, PROM D3 -is- D3, PROM A0 -is- A0, PROM A8 -is- A8, etc. (Bearing in mind that system D4-D7 will actually go to D0-D3 on one of the two PROMs).

I have a device programmer which can read and program most of the PROMs which are pin compatible with the MK14, I have programmed quite a few sets without problems and certainly without having to rearrange the order of bits or addresses in the code. If reading the PROMS you can make your life a little bit easier by making a jig with the high and low PROM wired side by side so you can read the contents of each address from both PROMs as a single 8-bit byte, as that will be easier to compare with the monitor listing (your 'Old' OS PROMs should match the listing in the MK14 V1 manual).

Last edited by SiriusHardware; 11th Nov 2020 at 6:10 pm.
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Old 12th Nov 2020, 12:31 am   #110
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Default Re: I found it! A very sorry looking MK14.

I tried remove each RAM chip one at a time, I only have the standard pair of RAM fitted. Result in both cases was all segments on bright on the rightmost digit and all segments on dim on the second from right. I didn’t want to try leaving it running like that for long enough to take pictures.

When I was first trying to get my MK14 running again, before I replaced the RAM chips, it was still showing four digits and two digits in the correct place but stepping through memory would make it jump to random addresses on the display. I was fairly sure it was a RAM issue, which turned out to be the case, but it was only partially faulty RAM.
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Old 12th Nov 2020, 5:46 am   #111
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Default Re: I found it! A very sorry looking MK14.

With 0,1, or 2 RAM chips I get the same result, 'X XXX XX', where X is a flickering digit.

With no ROMs, I get all digits, all segs.

In a few days I'm getting a set of brand spanking new TTL chips, so I can replace all those vintage bits.

I don't remember having all these problems 40 years ago.

This retro computing was easier when it was cutting edge.

Cheers,

Buzby
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Old 13th Nov 2020, 10:16 pm   #112
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Default Re: I found it! A very sorry looking MK14.

I've dug up my drawing for a 2-PROM to 2716 adaptor (for the purposes of reading a pair of PROMs as though they are a 2716 in an EPROM programmer) - I've tidied it up a bit and thickened all the lines so that it will hopefully still be readable after the forum has crunched it down.
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Old 16th Nov 2020, 2:36 pm   #113
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Default Re: I found it! A very sorry looking MK14.

Well, I've replaced every TTL chip in Vicky with a brand new one, but no change in behaviour.

I've tried every combination of my four 2111s, but no change in behaviour.

The only change comes if I swap 'old' for 'new' ROMs, but neither set gives sensible results.
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Old 16th Nov 2020, 11:52 pm   #114
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Default Re: I found it! A very sorry looking MK14.

The display pic you posted (for SCIOS?) showed the dominant binary pattern x0F.
What is the different (SCMPKB?) display?
The Display/Keyboard code in both monitors is the same.
From Reset, SCIOS would be outputting '0000__00' and SCMPKB '----__--'.
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Old 17th Nov 2020, 6:01 pm   #115
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Default Re: I found it! A very sorry looking MK14.

While we await the outcome of other avenues of investigation, earlier on, you said that you had tried 'exercising' the upper address lines and scoping the _CE signals for activity, which you did see.

I suggest that you now need to specifically check whether address A8-A11 state =nnnn actually results in the expected _CE signal being activated, so,

xxxx1111xxxxxxxx (0Fxx) should activate both _CE pins on the standard RAM ICs

xxxx1011xxxxxxxx (0Bxx) should activate both _CE pins on the extra RAM ICs

xxxx1000xxxxxxxx (08xx) should activate _CE on the RAM I/O

xxxx110100000000 (0D00) should activate the strobe signals to the display output hardware. For this last one you will probably need to assert NWDS low as well once the address is established.
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Old 4th Dec 2020, 8:28 pm   #116
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Default Re: I found it! A very sorry looking MK14.

A little update on this - as has been mentioned in PMs, Buzby's PROMs - both sets - turned out to be OK, so I sent them back to him and I've just received his 4 * 2111 RAMs for testing.

Unfortunately all four of the 2111s have turned out to be dud. I have some of the IM65X61 RAMs which the issue VI (only) can use as alternatives and I'll be happy to let Buzby have four of those, but of course he will still need actual 2111s for the resurrection of his original Mega MK14.

Does anyone know where they, or AMD AM9111s can be had for sensible money at the moment?
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Old 4th Dec 2020, 10:24 pm   #117
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Default Re: I found it! A very sorry looking MK14.

I did have the Am9111bpc in my cart at utsource but I just checked and its no longer there. I think they were listed at usd $2.70. Tried searching again but the price was up to usd $5.33 and showing as certified used. Best option now is listed under P2111A-4 for usd $2.83 also certified used but shows picture of AM9111BPC. I placed my order with ten of these included, take a chance on what I get.

Last set I ordered didnít originally state certified used but in my order history this is now showing, but the parts looked unused to me.

Local shop has AM9111BPC at cad $15 each, AM9111CPC at cad $7 each and SYP2111A-2 at cad $7 each. Iíll consider this if the utsource parts are no good but donít think its worth shipping to uk at those prices.

Utsource also list the AM27S13/BEA as third part original at usd $2.13 each so Iím taking a chance on ten of those too.

Shipping cost is a bit high and then probably customs handling and duty, but I have lots of other things included to help absorb that overhead.
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Old 4th Dec 2020, 10:31 pm   #118
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Default Re: I found it! A very sorry looking MK14.

I notice that Cricklewood (a respected old component supplier in the UK) have them:

https://www.cricklewoodelectronics.com/2111.html

That's pretty expensive, though. What I found interesting is their statement that the 2111 is an equivalent of the TMS4035NL - that's an equivalent I had not stumbled across until now.

Edit: Information from circuitryboy, the information above is incorrect, the TMS4042NL is the 2111 equivalent device, not the TMS4035NL as stated above and on Cricklewood's website.
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Old 4th Dec 2020, 11:56 pm   #119
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Default Re: I found it! A very sorry looking MK14.

All thanks to Sirius for testing my PROMs and RAMs.

I can get Vicky working with 6561s, and I don't mind that. For Vicky, function is more important than form.

Micky will need 2111s, but I've still got other work to do before I need to fit RAM.

This project has been a real PITA. I've spent lots of time and money on it, and the end result, if I ever get there, will be my 42 year old 'computer' working just as it did 42 years ago.

Why am I doing this ?
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Old 5th Dec 2020, 12:29 am   #120
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Default Re: I found it! A very sorry looking MK14.

Quote:
Originally Posted by Buzby123 View Post
Why am I doing this ?
Simply this:-

>the end result will be my 42 year old 'computer'
>working just as it did 42 years ago.

There is no higher or more noble reason.

Joking aside, if you get Micky working either in its highly customised form or just in its original single-board form, the increase in the value of that machine should greatly outweigh what you've spent on new TTL etc, and actually all of that new TTL can stay in the replica which will then have a re-sale value in its own right.
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