System 5 CPU board, prototype or homebrew?

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BasV_NL
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System 5 CPU board, prototype or homebrew?

Post by BasV_NL »

Hi all,

Recently I aquired an original System 5 computer.
The serie nr 04-H56-000010

Inside the S5 there is a interesting CPU board.

Do you guys recon it is a prototype or a homebrew CPU board?
(Pictures attached)

I do not know anything about the history of this System5 except that it was stored under a kitchentable for 20 years...Until In"found" it. It does not work and also did not work 20 years ago.

All info/thoughts are welcome.
Attachments
A41EC182-95C9-4713-93DD-F26DACBEA4A5.jpeg
FE920626-F886-4176-BC47-30CD61A55897.jpeg
B23BADE2-0303-4820-9987-8DBDAE0DEC51.jpeg
Kind regards, Bas
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Pernod
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Re: System 5 CPU board, prototype or homebrew?

Post by Pernod »

It looks functionally identical to a production board at https://chrisacorns.computinghistory.or ... 02CPU.html, so maybe an early prototype.

I'd be interested in seeing the ROM dumped.
- Nigel

BBC Model B: ATPL Sidewise, Acorn Speech, 2xWatford Floppy Drives, AMX Mouse, Viglen case, BeebZIF, etc.
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jms2
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Re: System 5 CPU board, prototype or homebrew?

Post by jms2 »

I don’t know about the board but I’m interested in the story of how it was discovered. I am wondering who keeps a non-working computer (which is already 20 years old) under their kitchen table for 20 years?!
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arg
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Re: System 5 CPU board, prototype or homebrew?

Post by arg »

I'm inclined to suspect it as a home brew clone, on the grounds that:
  • Some of the chips appear to have 1984 date codes. System 5 was prototyped during 1981 and 'production' PCBs existed in early 1982 (even though they didn't work very well).
  • It's double-sided but without plated holes (using soldered links in the through holes). This wasn't a technique generally used at Acorn at that time: first prototypes were usually wire-wrap, followed by PTH PCBs.
  • No part number on the PCB (compared to the production one linked earlier). By that time the Drawing Office was fully instituted and all products had part numbers.
  • The blue IDC header for the keyboard cable looks not to be the ones Acorn used (I can't remember which vendor it was, maybe 3M?)
Note of that is completely definitive, but taken together make me suspicious.

The case and keyboard on the other hand look authentic.
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BasV_NL
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Re: System 5 CPU board, prototype or homebrew?

Post by BasV_NL »

Pernod wrote:
Tue Jun 21, 2022 11:32 pm
It looks functionally identical to a production board at https://chrisacorns.computinghistory.or ... 02CPU.html, so maybe an early prototype.

I'd be interested in seeing the ROM dumped.
The ROM is 100% the same as the so called: Econet 3.40 NOS V.III (Chris Oddys checked this for me)
Kind regards, Bas
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BasV_NL
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Re: System 5 CPU board, prototype or homebrew?

Post by BasV_NL »

jms2 wrote:
Wed Jun 22, 2022 6:28 am
I don’t know about the board but I’m interested in the story of how it was discovered. I am wondering who keeps a non-working computer (which is already 20 years old) under their kitchen table for 20 years?!
Good story indeed,

Call them crazy, call them genius, the rebels, Mavericks ... oh sorry that is another brand ;-)
Some people do keep System 5s under their kitchen tables. :-) They do exsist! But you have to find them.

I saw this computer some years ago from the corner of my eye just standing there under the kitchentable when I visited my Acorn friend for the first time. It took me a couple of years to convince the him that it was okay to sell it to me. Since we know each other already for 30 years from the "Acorn-scene" we have build up a good relationship. But parting from the System 5 was difficult for him. "The precious" long long stiry short...Now I will take care of it. I will get it working and show it on the national Acorn shows and/or regional Big Ben Club days.

For him that will be the dream come true. His S5 working!
The faults in this System 5 where/are to challeging for him to fix. So I sure he will be proud when we get this machine up and runnig and show it of. In the Netherlands this is a very very rare machine. Maybe the only one.

Timo H and Roland L are my friends who are supporting me with advise and support. And ofcourse Chris Oddy also is looking over the shoulder :-)
Nice project for the next months tbc.
Kind regards, Bas
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BasV_NL
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Re: System 5 CPU board, prototype or homebrew?

Post by BasV_NL »

arg wrote:
Wed Jun 22, 2022 10:28 pm
I'm inclined to suspect it as a home brew clone, on the grounds that:
  • Some of the chips appear to have 1984 date codes. System 5 was prototyped during 1981 and 'production' PCBs existed in early 1982 (even though they didn't work very well).

    BV True... however some chips has been changed by other (old ones) for fault finding purpose.
  • It's double-sided but without plated holes (using soldered links in the through holes). This wasn't a technique generally used at Acorn at that time: first prototypes were usually wire-wrap, followed by PTH PCBs.

    BV If you say so I have to believe you.
    I find the soldering pretty badly done. Does not look professional to me. Also the etching is done not in a professional way....A bit like I did it myself at 16 year old ;-)
  • No part number on the PCB (compared to the production one linked earlier). By that time the Drawing Office was fully instituted and all products had part numbers.
  • The blue IDC header for the keyboard cable looks not to be the ones Acorn used (I can't remember which vendor it was, maybe 3M?)
BV Indeed no partnumber, brandname nor any other lettering can be found on the card.


Note of that is completely definitive, but taken together make me suspicious.

BV You are right and your ideas are almost in-line with my thinking. However...The thing is that i still find it a very strange story. the system 5 was not sold as a kit (right?) so why do I have here is an almost complete original case with original production cards (VDU, Econet, RAM ) (all ICs with 1981 1982 date codes) keyboard, PSU ect ....but no original CPU card???
Where did the original card go? And why did someone had to make a homebrew card with many botchwires only a few years (?) after the release of this machine...?

It does not make sense to me.



The case and keyboard on the other hand look authentic.

BV These are genuine parts no doubt. Everything is the real thing except the CPU card is a mistery.

Kind regards, Bas
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jms2
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Re: System 5 CPU board, prototype or homebrew?

Post by jms2 »

BasV_NL wrote:
Thu Jun 23, 2022 5:50 pm
I saw this computer some years ago from the corner of my eye just standing there under the kitchentable when I visited my Acorn friend
Ok, now it makes a bit more sense. I thought maybe it was someone who didn't even realise what it was!

I'm sure that you and your excellent support team will be able to fix it.
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arg
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Re: System 5 CPU board, prototype or homebrew?

Post by arg »

BasV_NL wrote:
Thu Jun 23, 2022 8:48 pm
BV You are right and your ideas are almost in-line with my thinking. However...The thing is that i still find it a very strange story. the system 5 was not sold as a kit (right?) so why do I have here is an almost complete original case with original production cards (VDU, Econet, RAM ) (all ICs with 1981 1982 date codes) keyboard, PSU ect ....but no original CPU card???
Where did the original card go? And why did someone had to make a homebrew card with many botchwires only a few years (?) after the release of this machine...?
Yes, it is very odd. The S5 wasn't sold as a kit AFAIK, indeed they were hardly sold at all apart from as Econet fileservers; it took much longer than expected to make them actually work properly and there was a big list of official modifications to fix it.

So it slightly makes sense for the card to have bodge wires if they accidentally copied the original official design and then had to apply the same bodges to it.

The case was mostly off-the-shelf parts from Vero (the 19" rack and the card covers etc.), but that front panel "Acorn System 5" was obviously custom Acorn and would have been hard to duplicate.

The other cards also look a bit non-standard: the Econet card has apparently had a toggle switch added to it, and then what is that "Econet Clock" card?

Also, I thought the video cards usually had a BNC connector for the video rather than the phono on that one (though that could have been an official cost saving measure, I'm thinking more of S3 and S4 machines).


The backplane is also worth a look: my fuzzy memory from that time was that the backplane for the S5 was special. Did it distribute higher frequency clocks from the CPU card to the DRAM card? And did those high frequency clocks cause trouble requiring the backplane to be redesigned?
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