[sdiy] Jp-8 head scratcher

[Adam Inglis]

Maybe try deliberately detuning those oscillators by the opposite  
amount in calibration mode, and see what Compu-tune does then? Might  
be a workaround!

Adam
On 07/11/2013, at 9:14 PM, Maarten Halmans wrote:

> Hello All.
>
>> So you have *only* the KCV input driving the VCO pitch ?
>> Even after it leaves auto-tune ?
>> And it still has an error, even if you move the voice card to a  
>> different
>> location ?
>
> Yes I disconnected all modulation sources and the problem still  
> persists! Moving the card moves the problem, so this rules out  
> wiring, module controller board, interface board and cpu board. I  
> moved the board serveral times because the problem I am having  
> points more to these boards than to the voice board. I also replaced  
> the tuning multiplexers, cv summing amp, transistor array.
>
>> Could there be some kind of HF oscillation coming from somewhere  
>> that's
>> affecting the tuning ?
>
> I looked with my scope at the cv summing amp, tuning output of the  
> oscillator but I don't see any oscillations nor on other places in  
> the tuning circuit (sample&holds multiplexers etc).
> When I look at the output of the comparator which goes to the  
> counter I see no difference between working and bad channels. I also  
> compared the output of the cv summing amp of the channels but the  
> slew rate is the same. I stop the repair for now because I keep  
> running in circles and keep testing the same things. But suggestions  
> are still more than welcome.
>
> Best,
> Maarten
>
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