Godwin String Concert SC 749 Fixed
Here at Vintage Keys Studio, I spend a fair amount of time keeping the keyboards in working order. Some of the organs and pianos we have are so rare that it is becoming increasingly difficult to source original schematic drawings / service manuals! A lot of time has been spent in the past pulling my hair out - the worst case was our Hammond M102, which had a fault with the pedal sounds. After hours and £££ spent trying to replace things, it turned out that it was a faulty resistor, which cost about 5p to replace! Duh! My only excuse is that I am first and foremost a musician, and only began fixing keyboards and stuff a few years back after a car accident rearranged my brain a bit and made me suddenly able to understand electronics!
The Godwin String Concert from the mid 70s, made by Sisme, Italy is a great, warm analog string synth, capable of 3 sets of string sounds at once (3 octaves, Cello 16', Viola 8' and Violin 4'). When we originally purchased this synth, none of the 'Gs worked at all, and a couple of the others were unstable.
After some problem finding (connecting the pin outs of the master octave divider to different notes) I ascertained that it was the top octave synthesizer IC (MK50240) at fault, rather than the main oscillator.
The problem was, the MK50240 IC is very hard to find these days, and when one does come up, if it still works, it is usually pretty expensive! I did find a modern equivalent which was great - the FK50240 by Flat Keys, but due to whatever reason [very likely a fault in the ageing and slightly rusty synth!], it wasn't 100% compatible with the String Concert.
After a bit of scouting around, I decided to try a cheaper M083B1 chip (cheap as chips!... or cherries..), which did approximately the same job as an MK50240, and voila! it worked! A bit of a gamble, but it paid off in the end. The chip in question is in the centre of the photo above, vertically positioned (PIN 1 is top left corner.)
So, if you ever get hold of one of these keyboards and a whole set of notes of the same name aren't working, chances are, it's the top octave synthesizer chip. Despite the Flat Keys chip not quite working for us, I would thoroughly recommend them. Their FK50240 is a great idea, and it also allows for additional functions, such as octave shifts/transposing, and their customer service is brilliant.
It took me ages to find the schematic for the SC 749, so here is a copy for you, for FREE... and it's.........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................here!
Cheers - Steve