VL2500 Spot Magenta Acting Oddly

[GoboMan]

I'm having an interesting problem with one of the VL2500 Spots in my rig. Whenever I power it up, it will calibrate as usual, but then when it opens its shutter the magenta is always in at near 100%. When I roll the encoder on the board to 100%, it will move but I will see it pass its endpoint and then end up at around 50% magenta. If I roll the encoder back to 0% and put the magenta wheel back to where it initially started and wait a few seconds, the magenta wheel will then automatically home itself to the correct 0% position. It will then behave correctly with the encoder and cues for the rest of the night.

Is this a sensor card issue or something else more complex? I opened it up and I can't see any damage to wiring or to the CMYD module itself. Something tells me it's not really the sensor card because it does eventually figure out where the home position is, but only after I roll the encoder to full and back a few times, so that tells me the sensor card is actually working.

I would like to try to get a little more information before I start taking things apart. Thanks!

 

[JD]

Sounds like a cold fail issue on the home sensor if it only happens on a cold start.
Next test- Shut the unit down after a nice workout when it's working. Restart the unit while it's nice and warm and see how it initializes. If it's temprature related, it will work. If not, then further digging is necessary.
If the unit works when warm, it's time to get the freeze spray out.

 

[GoboMan]

Sounds like a cold fail issue on the home sensor if it only happens on a cold start.
Next test- Shut the unit down after a nice workout when it's working. Restart the unit while it's nice and warm and see how it initializes. If it's temprature related, it will work. If not, then further digging is necessary.
If the unit works when warm, it's time to get the freeze spray out.

Thanks, JD! Once the house is all clear tonight I will do a warm restart on it and get back to you.

 

[Les]

I spent a few hours today servicing a grumpy VL500. The pan was being all jittery and sounded like it was hitting an obstruction during the homing sequence. After checking the belt tension, digging through my parts drawer and replacing the motor, followed by the sensor, and still having issues, I turned my attention to the MCB. I swapped the MCB with a spare and it works fine now.

I looked closely at the pan motor driver (which is SMD) and noticed that all the legs on one side of the chip had lifted from the pads. Not sure if it was thermal or mechanical stress that did it, but at least I found the culprit and that it is repairable.

While my issue could be totally unrelated from the problems you're having, my suggestion is to take a close look at that driver chip and see if there's anything unusual going on. If it's thermal, there could be an issue of a cold solder joint intermittently lifting itself or something like that.

Admittedly, yours might be more likely to be an issue in the sensor. Especially if it's working okay a lot of the time.

 

[GoboMan]

UPDATE: So after the house cleared tonight I lamped off the fixture and waited about 15 minutes (to avoid damaging the lamp from an immediate re-strike) before shutting it off. After being on for almost eight hours I figured the unit would still be plenty warm. I restarted it, and after calibration, not only did the fixture open up in near full magenta, but the cyan wheel was now also a bit off, and I did the same method in my previous post to get them to home correctly. Obviously, those wheels are not calibrating correctly. It's almost like the sensor card can't find the homing mark on the wheels until I show it where it is.

 

[porkchop]

It's worth getting to the light and watching this happen while homing, preferably without the lamp struck for safety. It's possible there is a physical issue like a worn belt or a set screw that has back off. Look for the simple stuff before diving into the weeds on hard problems.