On 7/9/2015 4:51 PM, Bob Grieb
bobgrieb@... [chromapolaris] wrote:
> Until Paul jumps in, I guess anyone can throw out ideas,
> so I will...
>
> The output of each synth channel goes through a 4053 MUX to create
> main out and alt out. Did you replace those on the two offending
> voices?
Yes, that was part of the "all ICs" on the offending voices.
> Also, did you scope the signal coming out of the
> "tune buffer" and also the signal at the output of the 1489 Z46?
> I know that those are not specific to particular voices, but maybe if
> they are bad, some voices could be more affected than others?
Yah, the ZCD signal looks the same for all oscillators.
Tomorrow I start measuring resistors & checking traces.
Will also look further back in the data lines to see if any disturbances
there might be causing some trouble.
~G
>
> Bob
>
> ------------------------------------------------------------------------
> ∗From:∗ "klosmon klosmon@... [chromapolaris]"
> <chromapolaris@yahoogroups.com>
> ∗To:∗ chromapolaris@yahoogroups.com
> ∗Sent:∗ Thursday, July 9, 2015 5:04 PM
> ∗Subject:∗ [chromapolaris] Polaris stubborn! tuning problems
>
> Currently working on a Polaris that was severely mistreated.
> Replaced the membrane panels, several pots; upgraded the ROMs; tuned &
> scaled the power supply, DAC, CPU and voice board per the service manual.
>
> Two voices (3 and 5) will not pass tune. Re-enabling them shows that
> Oscillator B on both voices scales sharp towards the upper part of the
> keyboard; also, when playing the filter resonance from the keyboard,
> those two voices are out of tune with the rest.
>
> What I've done so far: swapped out ALL ICs on the two offending voices
> -- no change.
> Swapped out all the sample/hold caps and oscillator timing caps on the
> two offending voices -- no change.
> Replaced the four ICs (Z60 - 63) in the sample/hold control circuit --
> no change.
>
> At this point, I'm out of ideas as to why these two voices are behaving
> this way.
> All memory functions, internal and external controls, and other synth
> features are working correctly on all voices.
>
> Any suggestions?
> Thanks.
> ~GMM
>
>
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