[sdiy] Jupiter-6 Osc Sync?

[Tom Wiltshire]

I wondered that too. That custom chip next door to get the signal  
levels right and deal with the sync just looks like a kludge. Makes  
you start to think they must have had a reason.

T.

On 10 Feb 2010, at 23:51, Doug Terrebonne wrote:

> 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
>
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