Stepper Motor Driver Problems

[chrisprescott]

I am trying to get some Martin PAL 1200 Scanners working. They all lamp up fine and mostly respond to the desk commands they are sent. They are all in the correct profile and addressed correctly as one fixture (ie dpr2 off).

 

However a few attributes seem to either respond erratically ie: gobo rotate is not very smooth at low speed or pan or tilt have a jitter and a few attributes do not respond at all. I have tried different modules and boards but have now exhausted my supply of spare boards from two donner lights. So I am looking at component level repair now. Im guessing I can use the other ICs of the spare boards?

 

Can anyone confirm this is likely the driver ICs as I suspect or if anything else is likely, and is it caused by stepper motor failure or something else which requires rectification before IC replacement.

 

Cheers

 

Chris

[Ben]

Hi

 

This could well be the stepper drivers failing, this is normally due to age and you should be ok just swapping with a new one unless they have physically blown up in which case you should investigate first.

 

This could just as easily be the motors themselves failing and the drives may be fine. easiest way to find out what is wrong is to start swapping the parts and see what happens.

 

HTH

 

Ben

[johnhuson]

As Ben says it could well be stepper drivers failing, no harm in swapping like for like to see if it is. With the gobo rotate juddering you might also want to check that the bearings are suitably lubricated if you haven't already as this can also cause juddery rotation.

 

Good luck, they're certainly classic fixtures!

[chrisprescott]

Could anyone reccomend what to lubricate the bearings with? Is there a special Martin grease? I have tended to use sewing machine oil on moving parts before.

[gyro_gearloose]

What makes you think the ICs are the cause of the fault? Its more likely that the motors themselves are worn out. They get exposed to alot of heat, and heat damage to the motors will cause the symptons you've described.

 

Try removing a motor and turning it by hand. It should be very easy to turn, and you should feel the individual steps as you turn the shaft. If its at all hard or impossible to turn, then the motor needs to be replaced. Oil/grease will only be a very short term fix at best. The heat will evaporate most oils quite quickly.

[marktownend]

Never been inside a PAL but if they're anything like the old Roboscan 1220s, it could be that the pins within the connectors are breaking up. For each function the 1220s have a 6 way lead coming from a 6 pin connector on the PCB to a 6 way connector linking onto the stepper motor.

 

I found that the pins inside the connectors (normally at the stepper motor end as they run hotter and get gunk in them) can randomly disintegrate.

 

The way to check if you're unsure is to unplug the white connector, then carefully remove each of the 6 individual wires (in turn - don't mix them up!) from the connector and check the er, "spring clip thing" that's crimped onto the end of the wire. If it's broken, then there's your problem! Note that just putting a tester onto the back of the connector to check continuity won't help, as it's right at the tip of the "springy clip thing" that they break.

 

Hope this helps - if the PAL is nothing like this then sorry for the waffle.