Optical Sensor Issue

[partyanimallighting]

Hi guys, I need some advice on a problematic moving head unit. So......I pulled four of these units out of storage after two years to give them a little test run seeing that things are getting a little active (until the next wave) and three worked fine but on one unit I'm getting a bouncing and grating tilt. I've resolved this issue in the past yes, the problems ranged from dirty optical sensors, bad solder traces, broken hall sensors or broken harness wires but this unit is testing my patience. The photo shows the hall sensor PCB at the top circled in red and the optical sensor and wheel circled in yellow on the bottom. So far I've done the basics: I've cleaned the sensors, I resoldered all the solder points on both sensors and at the harness terminals, I've tested solder traces on the PCB's looking for cold solder points, I've tested the 3-pin harness wires for continuity from the optical sensor PCB to the hall sensor PCB and also the 4-pin harness wire from the hall sensor through the arm into the PAN/TILT PCB located in the base of the unit. I've also swapped out the PAN/TILT PCB with a known working PCB but the problem remains. The unit starts up fine but the tilt does not home to 90 degree vertical (no DMX signal in) but remains a little off, I would say 75 degrees. When I forcefully tilt the head upright, it rehomes back to the 75 degree position (which is what it's supposed to do, except at 90 degrees) so the optical sensor is reading the wheel count, but reading it wrong. My next step is the remove the optical sensor PCB and replace the sensors once I have the correct replacement optical sensor in stock. Is there anything you wizards would recommend before I try this last step? Is there another issue that would cause the problem that I don't know about?

 

[Bluejets]

Not running it with the cover off and exposed to mains lighting or sunlight by any chance..??

 

[partyanimallighting]

Exposed to workbench lighting yes. But I am quite sure the optical sensors aren't picking that up as the issue was there on the unit out of the flight case but I'll put the cover back on and start up to confirm.

 

[kellys_eye]

The circuitry should have a 'known position' sensor i.e. a 'zero point' in order to know where to step to when starting from switch on. It can't do it just by counting pulses from that wheel on its own.

Is the 'zero' point set (calibrated)? How does it know the zero position? Slot? Magnet?

 

[partyanimallighting]

So I assume the "zero point" position sensor would be the W41FC Hall Sensor located in the red circle in the first picture and this sensor picks up the magnetic field from the small magnet on the gear. I know that these sensors normally cause the same issue but the magnet is working fine and the sensor seems OK and I did resolder the solder points and checked the solder traces too. The sensor has 4 pins but it uses a 3 wire harness fed from the optical sensor PCB and one pin is not used. However, the PAN Hall sensor harness has 4 wires, not sure why. I've attached a picture of the PAN Hall sensor just in case. Do you think I'm looking at a Hall sensor issue and not an optical sensor issue? I do have some replacement Hall sensors in stock but they're 3 pin and not the same part number.

 

[Bluejets]

The hall effect is a special purpose device with multiple operations so not your everyday run of the mill hall sensor.
AS such if you think it is defective it will require exact replacement device.

https://www.indiamart.com/proddetai...1fc-dc-brushless-fan-with-fg-21005318962.html

 

[kellys_eye]

but on one unit I'm getting a bouncing and grating tilt.

Have you eliminated the motor as the issue?

The unit starts up fine but the tilt does not home to 90 degree vertical (no DMX signal in) but remains a little off, I would say 75 degrees.

Sounds to me that the motor is getting the pulses but not doing the movement - could be the motor, could be the driver, could be the supply to the motor/driver.

 

[partyanimallighting]

Hi all. I eventually found the cause of the problem. A small nick in one of the harness wire leads caused intermittent contact at the cut. When I tested the harness for continuity the wire conveniently made contact but upon startup the movement of the pan/tilt would create the problem by pulling the cut apart sufficiently to break continuity.. Thanks again for all the advice.