Welson Syntex repair help

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Welson Syntex repair help

Postby electrotech » Tue Jul 10, 2018 8:04 pm

Hi,
Many years ago I bought this 1974 synth in a non-working state and it's previous owner had already had a go at repairing it without any success.
At the time, I too was unsuccessful - mainly due to inexperience plus not having the relevant schematic diagrams...
Recently, I thought I would have another go at repairing it after seeing a 'service manual' for sale from an on-line source but after receiving it, it turned out to be incomplete with the faulty section (Code Converter) not covered.
With the absence of any circuit details I would like to ask if anyone can verify that the two circuit boards pictured (MOD226 & W217) have all the correct IC's fitted in the correct place.
There is a possibility that some of them are the wrong ones as the IC numbers are easily confused with the date code !

Andy
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Re: Welson Syntex repair help

Postby blueknob » Wed Jul 11, 2018 11:19 am

Sadly I don't have any info, but as a fixer myself, that looks like a fun project to work on! Provided of course there are no time or business pressures. One thing in its favour, its all accessible, can be got at and worked out. All those logic chips the 74 series, can be worked out, I luv Boolean equations. :geek:

As you allude to, one killer problem is if the chips have been shuffled around (in the sockets), schematic or comparison needed.
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Re: Welson Syntex repair help

Postby electrotech » Thu Jul 19, 2018 12:48 pm

Hi,
Sorry I didn't reply sooner but I didn't receive any notification that there had been a reply...
Time to repair this isn't an issue for me as I'm retired now. Also, this is my own keyboard but it's literally been sitting in the to-do pile for years !
Some good news : a few days ago I managed to find a copy of the full set of circuit diagrams for the later 1976 version (They are 'blue-line' prints and were originally supplied by Welson UK many years ago) - however, the keyboard encoder and code converter are different from my one..
It certainly seems that schematics/circuit diagrams for this early version (using MOD226 & W217) code converter aren't available anywhere, so I've decided to reverse-engineer the boards I've got and compare them with the later code-converter (W.284 - and hope there aren't too many differences) then hopefully come up with the correct circuit.
I studied Boolean logic at college in the 80's so some reading up to refresh my memory will be required...
I'll update this page if/when there's some progress.

Cheers,
Andy
Last edited by electrotech on Mon Jul 30, 2018 8:29 am, edited 1 time in total.
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Re: Welson Syntex repair help

Postby Rasputin » Sun Jul 29, 2018 9:02 pm

This probably will not address the actual problem in the thread, but anyone trying to fix one of these will probably land here. So...

Welson Syntex - Service Manual PDF
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