In recent weeks I noticed one of my voicecards in P6 module sounded little off in some patches. I narrowed down the issue to poly mod not working on one of the cards. After patch init all seemed fine (all voices in tune) but as soon as I added poly mod amount to i.e. Freq 1, Shape, PW 1, it simply didn't do anything on just one voice, it still sounded like init. Neither repeated calibration nor the calibration table reset didn't help.
So my thouht was that perhaps the card needs to be re-seated or maybe the contacts need cleaning. I suspected voice card 1 to be the culprit - it was the first channel of MPE voice channels, channel 2. I just sent the MIDI notes in MPE mode, one channel at a time. So I assumed it would be the voice card 1 (since MIDI channel 1 is reserved to MPE status/system messages in MPE mode).
And indeed, I checked all the cards and found some contacts on the voice card 1 were little dirty. Cleaned it, re-seated everything back into slots and voilá, all is sunshine again

Leaving this info here in case someone finds it usefull in future
