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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 7th Mar 2020, 10:02 pm   #281
Slothie
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Default Re: MK14 schematic revisions

I was hooing that using a CMOS 2k ram chip it wouldnt load the bus enough to require buffering, but you might be right because the SOC VDU card might be loading the bus enough. Perhaps the improved power decoupling wll reduce the noise on the signal lines enough to increase the drive capabilities of the MK14. Or perhaps all the extra signals on the edge connector will make it worse Fortunately 4MHz isnt a high enough frequency to make track to track couoling a huge problem and most signals are much slower than that but some of the traces ate very close! Although I delibetately tried to make the spacing around the XOUT signal as large as possible.
I cant wait to get out of this hospital, build the board and poke about with a 'scope!
I also look forward to hearing how you get on getting the VDU to work, as I dont have one to test. I was going to solder a male DDIN41612ab connector edge-on to the edge connector for the ra.m board which would have one or two male vertical connectors so add ons like the VDU could be plugged in vertically. I sketched out a circuit on a notebook somewhere but got distracted working out how to utilise the "hidden" 512 bytes of the 2k ram!
I like the.idea of making a EPROM socket and switchable mapping of the addresses. If you dont fit the PROM and RAM chips to the main board then the decoding on the main board will be ignored.... Maybe a cut down version of NIBL could be made to work!!
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Old 8th Mar 2020, 1:38 pm   #282
Slothie
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Default Re: MK14 schematic revisions

I just found a list of part numbers for LED displays that are compatible in an old eBay saved search:
(nsa1198,nsa1188,als318,cqyp95,5082-744)
Note some 8 digit displays have 9 plastic bubbles, with no led under one of them so be careful!
Hope this is useful. At the moment Littlrdiode has nsa11
98 displays at their usual premium price!! (25)
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Old 8th Mar 2020, 1:48 pm   #283
SiriusHardware
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Default Re: MK14 schematic revisions

The cheapest ones currently available appear to be in Russia, but given Tim's illuminating experience with one of those I'm not sure I would want to go there. I can't believe how much basic, common LED calculators have jumped in price.
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Old 8th Mar 2020, 2:07 pm   #284
Slothie
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Default Re: MK14 schematic revisions

Quote:
Originally Posted by SiriusHardware View Post
The cheapest ones currently available appear to be in Russia, but given Tim's illuminating experience with one of those I'm not sure I would want to go there. I can't believe how much basic, common LED calculators have jumped in price.
The display i used came from the Ukraine and worked ok, i guess its just the luck of the draw. The psrts are just as old as any other, just languised in russian warehouses for decades! It appears they overproduced and didnt dare throw anything away.
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Old 8th Mar 2020, 3:33 pm   #285
hysteresis
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Default Re: MK14 schematic revisions

Quote:
Originally Posted by Slothie View Post
Note some 8 digit displays have 9 plastic bubbles, with no led under one of them...
Texas Instruments did the same with their TIL393 displays:
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Old 9th Mar 2020, 7:44 pm   #286
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Default Re: MK14 schematic revisions

My ICs are starting to arrive. The LS00 and LS08 (Ti parts) look authentic, even down to the patina of tarnish on the leads.

The 7445 and two extra 74LS157s, Nat Semi DM prefixed devices with the 'double wave' logo, look far too minty fresh to be true. I can practically see my reflection in the leads.

My device programmer has a 'chip test' mode for running basic functional tests on 74xx series, 4xxx series logic and assorted RAM ICs. I think I'd better test-drive all of these devices before I inflict them on any target system.
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Old 11th Mar 2020, 7:07 pm   #287
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Default Re: MK14 schematic revisions

Thanks to the generosity of 'KeithsTV' who kindly donated the necessary 7408 ICs, I now have the full complement of 'ordinary' ICs needed for this project. I just need to add up the numbers of IC pins and needed sockets which I will then order through work.

Contrary to the usual wisdom I think I will use conventional IC sockets rather than turned-pin types - of course the latter are better but they are also quite hard to desolder from a double sided PCB due to the way the large round upper portion of the socket pin snugly fits (and completely blocks) the through-hole on the top side.

With the PCBs being untested so far, I want to allow for the possibility of having to remove one or more of the sockets in order to effect modifications if needed.
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Old 11th Mar 2020, 7:43 pm   #288
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Now a further question: Does anyone know of a source for the 'stiff' 0.2" pitch ribbon cable which is traditionally used to mount the display? (note 18 cores spaced at 0.2", so two 'veroboard strips' apart). The cores are also usually solid single cores, unlike conventional ribbon cable which has stranded cores.
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Old 11th Mar 2020, 8:17 pm   #289
SiriusHardware
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Sorry, the above is incorrect (too late to edit). The cores in the strip need to be 0.1" apart, same spacing as the strips on veroboard, not 0.2" as I said above.
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Old 11th Mar 2020, 8:28 pm   #290
GrahamN
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Default Re: MK14 schematic revisions

How many ways?

See https://uk.farnell.com/te-connectivi...y-1/dp/1310328 for 10-way for example.
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Old 11th Mar 2020, 8:29 pm   #291
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Default Re: MK14 schematic revisions

Some more:

https://uk.farnell.com/w/c/cable-wir...r-pitch=2.54mm
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Old 11th Mar 2020, 8:47 pm   #292
SiriusHardware
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Thanks for the fast response GrahamN, that stuff looks perfect - 18 ways minimum, so this 20 way 1" length would be ideal (just have to cut two of the strips off).

https://uk.farnell.com/te-connectivi...y-1/dp/1310365

As a matter of interest, what did you use for the display connection on your JM replica?
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Old 11th Mar 2020, 8:52 pm   #293
GrahamN
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Default Re: MK14 schematic revisions

I bought a few Texet calculators cheap and used the display from one of those.
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Old 11th Mar 2020, 8:53 pm   #294
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If you can't make up an order I shall be buying some parts from Farnell on Monday or Tuesday next week - I'm happy to add to my order and post out to you.
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Old 11th Mar 2020, 9:04 pm   #295
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Default Re: MK14 schematic revisions

The offer is greatly appreciated but we order stuff from Farnell all the time at work, so I can just slide my order into the pile. Hopefully no-one will notice.

Thanks for spotting those ribbon connectors though, half of the battle is getting the wording of the search right. I've been looking for those for ages.

If your remaining calculators are in one piece and working you might want to consider re-selling them, you can probably (currently) get about four or five times what you paid for them.
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Old 11th Mar 2020, 9:40 pm   #296
GrahamN
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Default Re: MK14 schematic revisions

It would probably take me a month to find them! I have too much stuff for the size of my house. One day I'll start clearing some, but you never really know what's going to come in useful.
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Old 11th Mar 2020, 9:59 pm   #297
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Default Re: MK14 schematic revisions

Quote:
Originally Posted by SiriusHardware View Post
My ICs are starting to arrive. The LS00 and LS08 (Ti parts) look authentic, even down to the patina of tarnish on the leads.
I think you need to use 7408 not LS parts as they are not powerful enough to drive the traditional display otherwise.
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Old 11th Mar 2020, 10:03 pm   #298
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Default Re: MK14 schematic revisions

Yes, don't worry, I know that. The design requires two 7408s as display segment drivers and I have today received some 7408s from KeithsTV, but there is also a 74LS08 elsewhere in the circuit. That reminds me, check your PMs in a moment.
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Old 12th Mar 2020, 12:28 pm   #299
Slothie
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Default Re: MK14 schematic revisions

Quote:
Originally Posted by SiriusHardware View Post
Sorry, the above is incorrect (too late to edit). The cores in the strip need to be 0.1" apart, same spacing as the strips on veroboard, not 0.2" as I said above.
Its called "spectra strip" and farnell had it in multicolour form last year (stranded cire not solid, but still takes a shape well enough to work)
At a pinch you could use ordinary ribbon cable and only use every other conductor. Or make your odwn by stretching lengths of tinned copper wire over veroboard to get the spacing and sandwiching in gaffer tape to hold it all together.... I dud actually try this to fix an old calculator many years ago and it wirked "ok" but took a lot of csre tomake it look good.
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Old 12th Mar 2020, 1:10 pm   #300
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Default Re: MK14 schematic revisions

See the item linked to in #292 of this thread, pretty much perfect (although 20 way, so will need to have two cores cut off).
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