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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 3rd May 2021, 11:25 pm   #1
Timbucus
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Join Date: Mar 2019
Location: Barry, Vale of Glamorgan, Wales, UK.
Posts: 903
Default Heathkit Computers and the UK especially H8

I have alluded on some other threads that I may have picked up a major restoration project. I am going to post this as a quick update here and a plea for some opinions and help from the extensive knowledge here.

Here is the recent acquisition:

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- you can see why I have been a bit preoccupied the last week or two and have not built my SOFTY/INS8073 up or repaired my BBC yet.

Anyway - I do now have a very basic three card H8 running checking out 8K of RAM as OK. The H9 (terminal) and the H17 (disk drive) have some significant faults - this is one of the drives for example:

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So did the H8 itself but, that is a tale I may expand on in the thread - Many Tantalums, Cleaning and reseating chips, replacing many LS240, RAM fault - etc.

My main ask though is if anyone remembers seeing these advertised anywhere in the UK Electronics and Computing press - I was sort of vaguely aware of the Heath company and perhaps these machines in the late 70's but not sure how. I have come up short on much material that could explain how this unit was purchased and built by someone in the Monmouth area - the single disk it came with is dated 1979 so I would assume that it was not built all in one go (the chips on the H8 are all 1978) so it was around then it was constructed - and very well I will say.

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All the units have a lot of chip leg rot and rusty parts so this will be a long job.
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Old 4th May 2021, 12:51 am   #2
Mark1960
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Location: Kitchener, Ontario, Canada
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Default Re: Heathkit Computers and the UK especially H8

Not sure what you already found, but seems to be quite a lot on the net.

I have seen a few heathkit adverts in eti and practical electronics, but they were mostly adverts for the heathkit catalog. I had heard of the H8 but not sure if this was in a review or advert from the time or something I have seen more recently.

http://www.decodesystems.com/heathkit-h8-ad-1.gif

Schematic for ram and crt here:
https://www.vintage-radio.info/heathkit/

http://www.oldcomputers.net/heathkit-h8.html

https://wiki.theretrowagon.com/wiki/Heathkit_H8

https://museum.syssrc.com/artifact/118/
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Old 4th May 2021, 10:14 am   #3
Timbucus
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Join Date: Mar 2019
Location: Barry, Vale of Glamorgan, Wales, UK.
Posts: 903
Default Re: Heathkit Computers and the UK especially H8

Thanks Mark a few I had not found there - that CRT is the later H19 but, the 4k/8K RAM card is the one I have that has proven faulty and I do not have the schematic as they are supplied as a separate booklet I think which I do not have. I was lucky my 16K one was working as there is very little online but, I did find enough in this video to work out how to change the jumpers...

https://www.youtube.com/watch?v=zXcPWgkNLqo&t=590s

You are suffering the same thing as me it seems with adverts - any specific ads from the electronic mags that people have spotted would be great - it just seems that the fair number of issues I have on paper do not have any news or adverts - although each previous search including online I was not specifically looking. I may trawl the worldradio archive when I have a few hours to while away!

Anyway so this thread is useful to any other Heathkit computer owners you will rapidly come across the very active user group who have a sort of online archive:

https://sebhc.github.io/sebhc/

and an active google group:

https://groups.google.com/g/sebhc

I am going to see if I can work out why my 4K RAM is not working today -probably one or more of the 4Kx1 4044 RAM chips (it has new LS240 and each logic IC has been removed, cleaned and tested) they are helpfully called 443-832 by Heathkit but, they do list traditional numbers in the parts lists and in the pinout diagrams. Of course among the tens of memory chips I have there are none of them as spares...

I will say the the actual assembly Manuals are excellent - I was lucky to get quite a few with the machine but, not for all parts so lucky so many are online.

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It was a real joy last night to get it running as the split octal display on the front panel is unusual - it shows high and low bytes of the address / registers as two groups of three with a third group of three for the memory contents. For its time the Front Panel monitor is really well thought out and super easy to use say compared to the MK14 - but then again it was six times the price...

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They are not messing about with the 8v PSU capacitor either... the three rails (Other two are +/- 18v) are only half wave rectified and smoothed, cleverly the voltage regulators are on each card using the mounting rail as the heatsinks....

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Over the last week or two - I actually took the big Cap out and proved it out on a bench supply slowly - the smaller two I just checked for no short. As it was linear I removed and unplugged all boards and then just powered it up with a Dim Bulb and checked the rails were all stable for an hour or so prior to trying each panel in turn.
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