Robe 250AT Shutter error

[Neil Hampson]

We have 4 Robe250AT spots in the venue I design for however one of the units has come to me with an annoying shutter error. The 'lower' shutter keeps on getting thrown out of phase. I tried a new motor but no difference and I noted that that if the unit was reset and then not tilted, it did not error, but as soon as it tilts the error occurs. My thoughts then turned to the cable which I have now replaced with a known good one. The unit appeared to be working but every now and again it will open too far and then not close correctly as if the has rotated on the shaft a little. I have noticed that the top shutter has a top and bottom rubber bump stop but the lower shutter does not have a bump stop to prevent it from opening too far, (only on the close part) it's hard to tell as the blade goes between the gears of the prism and seemingly the prism shaft acts as the stop. I haven't yet been able to remove the front lens assembly to try to get into the thing better and I've not got another unit for comparison. I wonder if in the greater knowledge of the BlueRoom there is someone intimately familiar with these units that might be able to offer assistance in being able to dissasemble the unit further and if there is a bump stop that needs to be replaced.  Thanks in advance, Neil.

[KevinE]

You've checked pretty much everything I would do myself, (loom/motor); sometimes the clearance of the blades is a little tight and altthough they look ok, they can touch (say) one of the other wheels but only when they're at a certain position, colour or gobo etc. I would make sure the blades are perfectly free in all positions of the other effects. The only bump stop that's important is the one used for reset, if the other is missing or worn, it's just to stop damage or noise during transit. Once the shutter has reset properly against one bump stop it shouldn't ever touch the other one, since the program knows how many steps it can safely take.

As an aid in diagnosis I would write a little program to continuously rotate and exercise all the effects inclding the shutter and pan, keep the lamp off and see if there is any ticking or clanging at any point (notwithstanding if it crashes on the stops) that tells you the clearance is not right.

ISTR having a leaky capacitor on one of the stepper drive ICs that controlled the torque to one of the effects, meaning the motor was not increasing its torque during a movement and reducing it during a static state (as they often should). I cant remember if it was a Robe or Coemar or similar but it was a tricky fault to find.