[sdiy] Jp-8 head scratcher

[Maarten Halmans]

Hello,

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

Nah, tried that. Oscillators are tuned again to the same/wrong frequency. 
Cheers,
Maarten


> 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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