[sdiy] Jupiter-6 Osc Sync?

[Doug Terrebonne]

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 -

http://manuals.fdiskc.com/flat/Roland%20Jupiter-6%20Service%20Manual.pdf

The voice board schem is on page 16.

Thanks for any help,
Doug