Rhodes Chroma Polaris

> 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:
> 
> 11:53:37.336	From MIDISPORT 2x2 Port B	Pitch Wheel	
> 1	-1408
> 11:53:37.359	From MIDISPORT 2x2 Port B	Pitch Wheel	
> 1	-1152
> 11:53:37.696	From MIDISPORT 2x2 Port B	Pitch Wheel	
> 1	-896
> 11:53:37.718	From MIDISPORT 2x2 Port B	Pitch Wheel	
> 1	-768
> 11:53:37.730	From MIDISPORT 2x2 Port B	Pitch Wheel	
> 1	-640
> 11:53:38.099	From MIDISPORT 2x2 Port B	Pitch Wheel	
> 1	-512
> 11:53:38.258	From MIDISPORT 2x2 Port B	Pitch Wheel	
> 1	-896
> 11:53:38.437	From MIDISPORT 2x2 Port B	Pitch Wheel	
> 1	-1024
> 11:53:38.449	From MIDISPORT 2x2 Port B	Pitch 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@...