Mac 550 Dimmer

Colin Bishop

ValleyPoint Church AVL Tech
Nov 24, 2015
So I have a Mac 550 that dims poorly. It only turns on at about 50% and as such it looks off compared to my other ones. When strobing sometimes the dimmer will also end up in the wrong position, letting a little bit of light leak out at 0%, I have to reset the fixture to fix that issue but the dimmer curve will still end up off. I know it isn't a fixture setting cause I have checked it, but if you have a specific option you would like me to try let me know. I did adjust the calibration menu but it didn't help so I put it back at the defaults.

Any advice is appreciated!


Renting to Corporate One Fixture at a Time.
May 28, 2009
Phoenix, Az
Intensity is the word you are looking for. Dimmer is something that dims conventional fixtures.


I would start with replacing the lamp

If it continues then check your console to see if the channel is profiled wrong. (Best case scenario)

Most likely it’s your ballast though from the sounds of it. Due to the fact that you said your shutters are positioning back properly. It sounds like the fixture is having electrical issues.

Jeff Lelko

Active Member
Dec 13, 2014
Cape Canaveral, Florida
Why would you replace the lamp? This unit uses a mechanical dimmer.

My guess is either:

  • A shutter blade is loose on its shaft
  • The motor is reaching end of life and needs to be replaced (95% of the shutter motors I replace exhibit the symptoms you describe)
  • You have an electrical fault somewhere
If you're comfortable, take a look inside the unit and see if you can visually confirm the first bullet. More than likely it sounds like you need a new shutter motor though.

Good luck!


Well-Known Member
Jan 1, 2005
North Wales PA
My vote goes for shutter motor or mechanical hangup or shaft / blade slippage as well.
The key symptom is how it ends up out after strobing.

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