Martin MACiii performance dimming issue.

Hello all!
I recently purchased two MAC iii performance movers that were used (only way we can afford things). I love them but I am having an issue with one of them and I was wondering if anyone else has come across this problem. When fading out (but not fading up), about half way through the fade, the fixture has a flash as if it has restarted from full and started fading out again over the last 50 percent.
I have ordered new lamps for them since I know nothing about how many hours the lamps have burned. Might this get fixed when I put a new lamp in or is there a setting/calibration I have not found yet?
I did try resetting intensity calibration from the console to no effect. Thank you in advance for any suggestions you may have!
 
Swap lamps from a working fixture if that doesn’t do it then it’s not the lamp. That being said it could be a main board issue or possibly a ballast issue. This also sounds odd enough that you might not be controlling it properly and your programming could be making it jump up and down as it fades out.

I would take it down and test it in front of you and see if error codes pop up that will net more answers for us to help.
The manual if you don’t have it : https://www.martin.com/en/site_elements/martin-manuals-user-manual-hi-res
 
According to the manual posted by Amiers, this fixture has a discharge lamp and mechanical dimmer (flags and or an iris-like shutter which block more or less light). With that in mind, lamps shouldn’t matter, as the lamp keeps its constant output).
Have you tried addressing the problematic fixture to the same address as the good fixture? If both fixtures have the same address and the dimming issue exists on only one, then the problem is with the fixture. If giving the problematic fixture the same address as the good fixture fixes the dimming issue, then the problem is with the console.
There could be a dimmer profile or curve attached to the problematic address. Or you could have accidentally programmed your dimmer sequence incorrectly. If you run the dimmer in and out with the programmer of your console, do you have the same issue?
If it is a console issue, I’d bet it’s a non-linear dimmer profile. eg, channel at 50% may not be DMX output @ 50%.
 
I would guess that it's a mechanical issue with the dimmer flag(s) on the fixture. Open it up lamped off down on the deck and do the fade, and I'll bet you'll see the flags jump. I don't know a lot about these lights, but it could be a belt issue, set screw issue, motor issue, or possibly driver issue. If it's purely mechanical though, you may be able to see the problem and order the part or tighten the set screw.
 
Bad stepper motors will sometimes randomly skip or reverse a steps. I believe that unit has two steppers - one per flag. If it is just one misbehaving flag then it could be the step motor...or its wiring.
 
Speaking of musbehaving stepper motors, is it normal or recommended practice to lubricate a stepper motor?

I used to work at a place with a dozen technobeams that went through stepper motors like water.
Also refurbing some old lights that do ok after a couple of homes, but the first time through a pan tilt, they're anything but smooth.
 
I haven’t ripped that fixture apart before. With that said I would remove the module that has the dimming mechanism and move it to another fixture that has no issues. If you see the same issue in the know working fixture you know that the issue existing in the module.

If this is not the case and a known good working dimming module does the same thing it is going to be in the logic board. Likely it would be a bad driver chip for the dimming mechanism.

I doubt it would be a harness issue, if something is severed in the harness it would just not work.

If It’s in the module I would look over the manual to see what gives the dimming flags tension, in the older VL’s there was a spring and kind of Gromit that gave tension to the dimming flags.

I would manually run the dimmer to see if you hear any noise to pint point where the issue would be in the module.

I remember on the Mac 2k’s you could do a chip crunch on the driver chips on the logic board and it helped. This driver chips were not soldered in, so they could come loose and cause issues.
 
Thank you so much for all of the wonderful suggestions!! To answer the questions and steps I have tried:
@Amiers - did the lamp swap with no effect.
Also, checked for error codes. Thanks for the link!
@Mike Donovan - trying your address suggestion and checking dimmer profiles in the patch next.
@MRW Lights - unit is powered by a 220v circuit run from 40 amp feed. There are 3 outlets on the line and the problem unit is at the last outlet. Line feeds 2 MAC iii and one MAC 500.
@soundlight - I’ll try that out immediately after checking for erroneous dimmer curves in the patch.
@chawalang - right after soundlight’s suggestion, I’ll try manually running the dimmer up and down while at the unit to test for a physical malfunction with the flags. Then a “chip crunch”
Thank you all for your replies!!
I had to run the show as is, but since this is a new light to us, I only had a few questions from others about the offending unit. Show closes this weekend so I will have more time to do the more in depth suggestions!
 
We look forward to seeing the results
 

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