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Welson Syntex
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electrotech



Joined: Apr 24, 2013
Posts: 34
Location: Ayrshire Scotland

PostPosted: Sat Jul 07, 2018 4:34 am    Post subject: Welson Syntex
Subject description: repair help needed
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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It had suffered a PSU fault and many IC's had been replaced by it's previous owner - however when I got it some of them were actually missing from one of the pcb's...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 Sad
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


snippet.JPG
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part of Mod.229
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