We recently bought and installed an old Sensor 24x20Amp portable rack, with an MPE controller (hooked up to an Express 250 board, but I don't think that's relevant). I've noticed that some dimmers are behaving oddly.
The issue is this: some of the dimmers dim differently than the rest. The problem dimmers are off at 0%, and full on at 100%, but in between they're noticeably higher than others.
I did some measurements -- using self-test mode 850, and I think with the control board actually shut off, so there's no question about the board having some funny dimmer profile programmed for these dimmers. And I only measured dimmers that had a load on them at the time - I know measuring the voltage output of a dimmer that has no load can get you a meaningless number. At 50%, the other dimmers showed 55 volts; the problem dimmers showed 73 volts.
Which dimmers? Known affected ("bad") are #10 and 11; known good include 7, 8, 17, and 18. (Those random-seeming numbers that I tested are the ones in the neighborhood that had load on them.)
I swapped dimmer modules around, and the problem stayed with the address, so it's not a couple flaky dimmer modules.
Based on all that, I wonder if it's somehow all the dimmers in that pack that are on Phase B of the three-phase power, since Phase B feeds dimmers 9 through 16. I tried to test that, by cutting power and swapping incoming power cables A and B, but my notes from that test just say "that made things worse" - I didn't write down my measurements - so I swapped the cables back.
Any thoughts as to what the cause might be, and/or any useful next steps toward fixing it?
