Welson Syntex

[electrotech]

Hi,
This synth is a 1974 vintage monosynth made in Italy.
I bought it s/h nearly thirty(!) years ago in a non-working condition, failed to repair it at the time and so it got stuck in the back of a cupboard....
Since I know more about electronics now than I did then I thought I would give it another go.
It had suffered a PSU fault and many IC's had been replaced by it's previous owner - however when I got it some of them were actually missing from one of the pcb's...
The control circuitry is all digital using TTL.
The keyboard controller generates a six-bit code and the digital oscillators (two) use a twelve-bit code to generate the frequency (staircase ramp waveforms x 4).
Between them is the 'Code Converter' which in my version is made of many logic gates on two PCB's.... and this is the part that is faulty.
Welson had different versions of the code converter section - a later one-board solution was numbered Mod.284 - however, I have the earlier version using two boards :- Mod.226 & W217 and this section had been hacked about with and had the missing IC's...
I did not have the circuit diagram of these boards and since I didn't know what all of the IC's should be that probably explains why I couldn't fix it BITD...

What recently spurred me on to resurrect this synth was that I saw a service manual for sale from an on-line seller (this information was as rare as hens-teeth as far as I was concerned) so I bought it - but my joy at getting it turned to dismay when I discovered that the important information I needed covering the code converter was missing !
See the snippet below
So, the help I would like is for someone else who either owns (or has access to) one of these synths if they could take some photographs of the two PCB's in question (MOD226 and W217 along the back panel), then at least I would know what IC's were used.
Either that or the actual circuit/schematic diagram of course !

Thanks,
Andy

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snippet.JPG
Description:	part of Mod.229
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[fede_tich]

LINK 1
https://drive.google.com/file/d/12jYwN6S5544dGMcZVt55nzRNPyDhbaRW/view?usp=sharing

LINK 2
https://drive.google.com/file/d/1fW4xtpLmOZD0ns0GEZYHMkGrXoFEy8vN/view?usp=sharing

[blue hell]

Thanks &

Or :

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Welson Syntex Schematic .pdf
Description:	welson syntex schematics	Download (listen)
Filename:	Welson Syntex Schematic .pdf
Filesize:	19.46 MB
Downloaded:	50 Time(s)

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Welson_Syntex_Service_1974-75-76.pdf
Description:	welson syntex service	Download (listen)
Filename:	Welson_Syntex_Service_1974-75-76.pdf
Filesize:	81.71 MB
Downloaded:	58 Time(s)

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[electrotech]

Thanks 'fede_tich' for sharing this documentation - are you the Marco Molendi who remastered the drawings ?
Also thanks to Jan 'Blue Hell' for downloading them to the forum
I never got my Syntex working but did manage to get hold of an original service manual (white/blue prints supplied by Welson UK long ago) but this only covered the later 1976 version and I had been slowly trying to 'tidy up' the scans I made of this, but it looks like I've been beaten to it !
The synth I've got (with boards MOD226 & W217) must be very rare as I've been looking for years for information about it but this doesn't seem to exist ; no-one else has ever managed to come up with either circuits or photographs of the boards in question.
The circuit for the later code-converter (W284 in the documentation) I painstakingly entered into a logic simulator program and discovered that there was a mistake in the schematic as the outputs were nonsensical !
By trial and error, I found out that a connecting dot was missing from the diagram.... I'll update this thread after I've found the files with the corrected diagram.
UPDATE: the first picture is a photo of a fraction of the W284 Code Converter I entered into a simulation program (Multisim - sorry about the quality...).
The second picture shows where the 'dot' was missing from the circuit diagram.

Andy

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[fede_tich]

[electrotech]

For anybody that's interested, I thought I might as well post a couple of diagrams that I've been working on to aid the repair of this synth (must be the longest repair in history)....
The keyboard scanner and output latch or 'Memory Keyboard' W216 is the one I've re-drawn.
Before 'Fede-tich' posted those comprehensive manuals above, the available downloads were a bit rough so I used a scan of the W216/A circuit from the 1976 manual I had to create the new image.
It was made by re-arranging the text fonts and component symbols as originally drawn so as to make it look authentic.
I might update it once I've checked it against the actual circuit board as I've noticed that there are a couple of pins that are unconnected (TTL inputs) in the original diagram...
I've also included a logic state table which was compiled from the data I obtained using the circuit simulation I mentioned above and which has been verified against a hand written page I found in an existing manual.
I hope to finally get this finished this year as it's been taking far too long... and I'm running out of time !

Andy

[electrotech]

Hopefully, the above mentioned files will be attached below.

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W216.png
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Logic_State_Table.png
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[blue hell]