[sdiy] Christmas Projects - first results

Florian Anwander fanwander at mnet-online.de
Thu Dec 27 10:32:46 CET 2012

Am 21.12.2012 12:38, schrieb Florian Anwander:
> Repair a JP4 where one voice card sometimes does not react on pulswidth
> control - assumingly a loose connector solder joint on the main board (I
> will do this definitely, becauser that is a paid task)
Done :-)

This was ugly: it was not the pulswidth itself, but the saw (from which 
the pulswidth signal is derived) was not a saw but a spiked saw, which 
was caused by a broken CD4052.
The JP4 (like the SH-7) uses a VCO, which covers only the range of the 
keyboard + the bender, but not the full range including the keyboard 
transpose switch and the VCO octave switching. The latter functions are 
achieved by dividers after the initial VCO. The divided core frequency 
triggers a waveform shaper. For each octave setting the current, which 
feeds this shaper, is controlled by different resistors which again are 
switched via the mentioned CD4052. This 4052 had all gates shorted for 
the X-half of its switches (the 4052s Y-half still worked). So the saw 
shaper got much too much current and the saw was too short for the 
frequency. Which again led to a very narrow pulse wave.

> Modify my JP6: Split the resonance control for the second SVF (for
> disabling the resonance). And if I will be really coltish I want to
> think about adding a split delta votlagee for the second SVF (but this
> would required an adapter board that moves the two SVFs to different
> IR3109)
> Repair my OBXa, which hangs in the boot routine (I fear it means in the
> first place: replace all sockets on the digital board).

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