[sdiy] P5 VCO Output Level Low

Tom Wiltshire tom at electricdruid.net
Fri Mar 3 11:59:50 CET 2017

If it's happening on all waveforms, I'd be inclined to suspect the mix amps (CA3280) or the mix amp CV circuitry.

If he's tried different VCO chips, it doesn't sound like it's the actual VCO, so it must be downstream. There isn't a lot between there and the filter - the switches and the mix amps, and that's about it.


On 3 Mar 2017, at 10:27, Tony Kalomiris <weplar at gmail.com> wrote:

> Hi list, just a general query as I await arrival of said keyboard.
> Is this a documented, engineering change order. Never heard of this before.
> The problem is one of the voice VCO's (3340) has a consistently low output, in fact half the amplitude, or 5v pk-pk. The tech said he checked the common analog, swapped 3340's, checked psu, all check-out. I suggested something is loading it down further down the line. He desoldered the analog switches (waveform select, 4016's I gather), and practically socket every relevant i.c. in there - this guy's gone desoldering mad ever since I sold him my Denon Sc-7000!
> I am not asking to be spoon fed, but just for old times sake - I got out of this biz two years ago - I wouldn't mind a crack at his. Troubleshooting is my forte after all. I was just wondering if there was some revisions (oh this one is a 3.x?). or known problems , 4016' etc.
> Will post in here when I get it on the bench and check the obvious stuff, pcb traces, load Rx, etc.
> Oh he's tried old and new 3340's, he says. 
> a bientot,
> Tony K
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