Troubleshooting intermittent colour-wheel issue

[Paul O]

I have a number of old Mac350's that are used mainly for theatre work. One of them has developed an intermittent colour wheel issue where occasionally the colour wheel will lose it's registration mid-show and until I get a quiet moment in the show to send a reset it'll be outputting a different colour to the others.

 

I've just completed a week's run of a show and twice during the week this happened, the rest of the run it behaved perfectly.

 

Having got it back on my workbench and run some tests I've not yet got it to misbehave at all. The fixture has no errors, runs through self-tests quite happily and the drive belt for the colour wheel seems fine and is nice and taut.

 

Intermittent issues are always more difficult to diagnose, any thoughts what could be causing the problem other than the belt slipping?

 

Paul.

[indyld]

Sensor and/or sensor signal path fault are obviously more common. (If you are struggling to replicate it then it's hard to verify but swapping for a known good sensor from another unit would be a start.

Check sensor and associated items (magnet or whatever) for gunk.)

 

However, given the symptoms it does sound a little more like slippage somewhere or motor issues.

[DrV]

Could be a wire starting to get intermittent. It might miss a step or two when the head is in a certain position only.

[timmeh2]

Hi

 

Macs suffer from dry joints on the hall sensor PCBs which can cause intermittant position errors. Just try resoldering the legs of the hall switch before tearing the unit apart.

 

All the best

Timmeh

[Nicktaylor]

I dont have any old 250s now but annoyingly I did find that when hung a fault would occur, but go away when sitting on its base. Can you hang it in your workshop to allow anything like this to happen in front of your eyes!

[Jivemaster]

Are the colour filters the correct ones? Moving mirror lights lose odd steps when the mirror has been replaced by one that is too thick (hence heavy) could the dichroics be too big or too thick so that they lose steps occasionally.

[Paul O]

I re-soldered the hall sensor but couldn't get it to misbehave (albeit testing base-down on the bench).

 

It's currently in panto and has played up a few times so it's looking more like a loom issue- I'll investigate the loom when it gets back to base and see if I can locate the break.

[indyld]

Don't discount the actual motor itself along with the loom and driver system. :-)

[DrV]

Don't discount the actual motor itself along with the loom and driver system. :-)

Very true. With the power off the wheel should be almost completely free to turn. If it is at all 'lumpy' or 'notchy' then the bearings may be failing. You can feel the poles of the motor go past the stator but only just. Difficult to quantify but you could compare with a good one.

[sunray]

Don't discount the actual motor itself along with the loom and driver system. :-)

Very true. With the power off the wheel should be almost completely free to turn. If it is at all 'lumpy' or 'notchy' then the bearings may be failing. You can feel the poles of the motor go past the stator but only just. Difficult to quantify but you could compare with a good one.

The motors used on 812's, 518's etc had very prominent poles and the difference between good and bad was almost imperceptible. I had a set of tension gauges (for 3000 type relays etc) and was able to establish a guide. It saved a lot of wasted time in the end.