> From: jesseterry
>
> Hi, New Chroma Polaris user, and I've got a problem,
> wondering if any of you have an idea.
>
> I get random Pitch bend drift, like the following:
>
> 11:53:37.336From MIDISPORT 2x2 Port BPitch Wheel
> 1-1408
> 11:53:37.359From MIDISPORT 2x2 Port BPitch Wheel
> 1-1152
> 11:53:37.696From MIDISPORT 2x2 Port BPitch Wheel
> 1-896
> 11:53:37.718From MIDISPORT 2x2 Port BPitch Wheel
> 1-768
> 11:53:37.730From MIDISPORT 2x2 Port BPitch Wheel
> 1-640
> 11:53:38.099From MIDISPORT 2x2 Port BPitch Wheel
> 1-512
> 11:53:38.258From MIDISPORT 2x2 Port BPitch Wheel
> 1-896
> 11:53:38.437From MIDISPORT 2x2 Port BPitch Wheel
> 1-1024
> 11:53:38.449From MIDISPORT 2x2 Port BPitch Wheel
> 1-1152
>
> I've replaced the pitch bend and modulation pots, with no
> luck, and tried a different MIDI interface. I've recalibrated
> the pitch and mod levers with no luck.
>
> It seems to go away for a bit if I reset the Polaris, but
> eventually starts drifting again in spurts if I use the pitch
> level. I can workaround by setting the Pitch Bend Lever range
> to zero, but then I miss out on the pedal steel pitch bend fun.
>
> Any ideas?

You'll have to trace through the circuit with a meter, always measuring
relative to the same ground, preferably near the A/D converter on the
main board. The levers get their power from analog +12V on the panel
board, so see if that moves concurrently with your pitch wheel MIDI
output changing. The signals then go down to the main board, where
they're converted to digital using a reference derived from analog +5V,
so see if that moves. The reference is divided down from +5V with a
trimpot (R45), so see if the output of that is stable. It could also be
bad op-amps along the way, bad 4051 multiplexers, or even a bad A/D
converter (Z53).

--

Ciao, Paul D. DeRocco
Paul mailto:pderocco@...