[sdiy] Jupiter-6 Osc Sync?

[Doug Terrebonne]

Thanks for the explanation Florian! Turned out to be a broken trace on the board. I wonder why Roland didn't just use the built-in sync on the 3340?

Doug


----- Original Message ----
From: Florian Anwander <fanwander at mnet-online.de>
To: Doug Terrebonne <dougt55 at yahoo.com>
Cc: synth-diy <synth-diy at dropmix.xs4all.nl>
Sent: Wed, February 10, 2010 5:28:38 AM
Subject: Re: [sdiy] Jupiter-6 Osc Sync?

Hi Doug

> Hi, I've got a JP-6 here where on 1 voice VCO1<-VCO2 sync does not work. Sync in the other direction on that voice does work. Can anyone explain how the JP-6 does osc sync? It does not use the sync onboard the CEM3340 (the pins are tied to ground) and all the service manual says is "sync is accomplished by external connections"... The service manual is here -
If I am right, then basically the saw of VCO2 is sent to pin5 of IC34A. The saw is converted to a spike and this spike draws via pin7 the pin11 of the CEM3340 to low. This function is enabled by pin6 on this IC.

Does the SAW work on this VCO2 of this Voice? Does it "look good" on the oscilloscope? Does it work if the reverse sync is on.
Do the other waveforms work and look ok (they are all fed through IC34A).

If yes, then IC34 might not well seated or have a loose solderjoint.
Compare the signals at IC34A with other IC34's
Check, whether the saw reaches pin5, whether the controlsignal reaches pin 6 and whether the spike "leaves" pin 7.

If only the signal on pin7 is missing, then assumingly the dedicated circuit for the sync in IC34A is broken. You might rebuild it with discreet parts.

Florian