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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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3rd Nov 2017, 12:29 am | #21 |
No Longer a Member
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
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Re: Nascom repair - Looking for clues please
IF the 6264 is a useful part here, I'm pretty sure that is the same basic 8k. X 8 memory IC used inside the Dallas DS1225 battery backed NVram, it's in there with a controller IC, these are easy to program and remember the data when removed from the socket. Also, in some applications, like Tek scopes, the Fram type FM16w08 can be substituted for the DS1225 and programmers like the GQ-4x will program an FM16w08 if it is set for a DS1225, recently the manufacturers of the GQ-4x updated the supported IC list in this point. So perhaps the FM16w08 could be of help too.
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3rd Nov 2017, 11:15 am | #22 | |
Nonode
Join Date: Oct 2008
Location: Warsaw, Poland and Cambridge, UK
Posts: 2,681
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Re: Nascom repair - Looking for clues please
Quote:
It worked fine, with only very occasional data corruption problems. It was very cheap, as well, which was a big advantage at the time! Conclusion: if erasing EPROMs is a pain, a battery-backed RAM chip will work fine. Chris
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3rd Nov 2017, 6:01 pm | #23 |
Pentode
Join Date: Oct 2010
Location: Melton Mowbray, Leicestershire, UK.
Posts: 156
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Re: Nascom repair - Looking for clues please
Thanks for the interest folks it's great to get help and advice.
I've been over the board testing the 74 series chips with a tester and they all turned out OK. My tester can't do 74LS163s though so I rotated those around, still no success. I did the same with the 81 series buffers. So I've come to a halt for a while. Everything is fine but it's still not working. Cheers, Andy. |
4th Nov 2017, 10:56 am | #24 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,586
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Re: Nascom repair - Looking for clues please
It looks like you're back to trying to write some test code, or 'belling out' every single interconnection on the PCB in case the fault is a physical fault like a cracked track or failed through-hole connection. Not a task I would relish.
Some EPROM programmers of a certain vintage have an 'eprom emulator' mode where they provide a connector for a flying flat ribbon cable with a male DIL connector on the end of it: This plugs into the target system's EPROM socket and the EPROM programmer uses internal RAM to emulate the action of an EPROM, the advantage being that it only takes a few seconds to download altered / amended code to the programmer. If your own programmer(s) had this feature I'm sure you would already be using it, but it might be worth looking out for an old programmer with this feature. I have one unit which is a serial hex -> eprom emulator only, not a programmer, made by a little outfit called 'JPD' many years ago, and I also have a commercially made EPROM programmer made by ICE TECH which includes an EPROM emulator feature. There surely must still be a few of these around. You'll still eventually need an eraser of course: I wonder if you can now get UV LEDs which produce light of a suitable wavelength? My understanding is that some LEDs used in LED lighting actually natively emit UV, and they are coated in phosphor which converts the UV light into light of the required visible wavelength. Is anyone already working on a LED eprom eraser? |
23rd Nov 2017, 8:27 pm | #25 |
Pentode
Join Date: Jan 2013
Location: Nottingham, Notts. UK.
Posts: 228
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Re: Nascom repair - Looking for clues please
Hi Andy,
I've only just spotted this thread but in response to the supply voltages you've measured: What I have so far... I have the following voltages from the power supply :- 11.93V 4.79V -5.06V -12.06V If the supply rail measuring 4.79V is the 5V supply rail to the processor and other logic circuitry then this could well be the cause of the problems you are seeing. Before going any further I would look to sorting this issue out. Jerry |
23rd Nov 2017, 9:46 pm | #26 | |
Nonode
Join Date: Oct 2008
Location: Warsaw, Poland and Cambridge, UK
Posts: 2,681
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Re: Nascom repair - Looking for clues please
Quote:
White LEDs typically use a Gallium Nitride visible blue LED, around 460nm wavelength, with a phosphor coating to create white or other colours like pink. There's no UV involved. Chris
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23rd Nov 2017, 9:56 pm | #27 |
Pentode
Join Date: Oct 2010
Location: Melton Mowbray, Leicestershire, UK.
Posts: 156
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Re: Nascom repair - Looking for clues please
Hi Jerry,
Thanks for the suggestion. I have just tried running it again but with the 5V rail coming from a bench supply and I still see garbage. |
25th Nov 2017, 12:45 pm | #28 | |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,586
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Re: Nascom repair - Looking for clues please
Quote:
Acollins22, it might be worth going back to the vintage computer forums to this thread which you were involved in early on: http://www.vcfed.org/forum/showthread.php?60295-Nascom It has since developed into a fairly technical discussion about various aspects of the Nascom (1) and is still ongoing. You might find some useful clues there now. One thing which comes up over and over again in discussions I've read about the Nascoms (1) and (2) is their apparent sheer fussiness about individual ICs - in some cases replacing one apparently working IC with another working IC, or swapping two of the same ICs over in the machine, will cause a significant change. This is especially the case when it comes to the video circuits. |
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