[sdiy] Jp-8 head scratcher

[Jack Jackson]

So if I understand correctly.

1. You tune all 16 oscillators using the trimmers on the voice boards.
2. You press the auto tune and the software puts one voice card out of tune.
3. Osc 1 on Voice A is 12 cents out of tune, Osc 1 on Voice B is 6 cents out of tune.
4. You said the problem moves with the voice card, which suggests to me a voice card, not an autotune problem.

Could you try manually feeding the oscillators 1v and the input mixer and see whether the tuning problem is the same?

I'm not sure from the service manual if the Osc 1 from both voices on the card share the same CA3046, or if each Voice has it's own CA3046. 
If it's the former, then that's where I would be tempted to look. 



----------------------------------------
> From: diy at artefacts.nl
> To: synth-diy at dropmix.xs4all.nl
> Date: Fri, 8 Nov 2013 09:54:57 +0100
> Subject: Re: [sdiy] Jp-8 head scratcher
>
> 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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>>
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