Mac 600 Tilt Issues

[IanC]

I have 4 martin mac 600`s which all have to same fault. When moving at slow speed the tilt works fine, but if they are tilting at full speed the stepper motors struggle.

 

All toothed belts are in tact and I have swapped the pan and tilt driver chips over and the problem is still they same.

 

Has anybody else experienced this problem? if so help would be much appreciated

[Smiffy]

In what way do they struggle? They can't get through the full range of motion?

 

How fast are they moving? Really fast?

 

Do they have to move so fast?

 

Are the belts tight?

 

Do the motors move freely without power or is it a bit tight?

 

Are all the sensors clean and free from obstruction?

 

How do they react on a slow cue? Will they always find the right position?

 

Do they calibrate properly?

 

Do they work fine initially and then after some time do they start to get iffy? Or is it straight away?

 

Cheers

 

Smiffy

[IanC]

Thanks for your questions, I have added some answers if that helps any

 

In what way do they struggle? They can't get through the full range of motion?

With the fixture sat on its base. When they get to about 90^o the weight of the head pull against the motors

 

How fast are they moving? Really fast?

They are moving at full speed

 

Do they have to move so fast?

Yeah the problem happens when they are moving at there default speed

 

Are the belts tight?

I was under the impression the two springs set the tension to the rear of the stepper motors, then you just nip the screws up tight

 

Do the motors move freely without power or is it a bit tight?

Motors run free with power off

 

Are all the sensors clean and free from obstruction?

Encoders are free and sensors are clean no errors on display

How do they react on a slow cue? Will they always find the right position?

they keep trying till they find the right position

Do they calibrate properly?

When the fixtures are powered up they go through the start up sequence fine

 

Do they work fine initially and then after some time do they start to get iffy? Or is it straight away?

they show the fault immediatly when moving fast

 

Cheers

 

Smiffy

Edited July 18, 2010 by IanC

[Smiffy]

I'm erring on the side of the belt being loose. Whip the sides off and see whether the belts can be made any tighter.

 

HTH

 

Cheers

 

Smiffy

[IanC]

Thanks for your reply smiffy, im 100% the belts are not slipping.

 

I was wondering if one or both of the stepper motors could be faulty. Seem to be quite pricey so I was hoping to be certain since I dont have a working mac to try swapping the motors.

 

I'm erring on the side of the belt being loose. Whip the sides off and see whether the belts can be made any tighter.

 

HTH

 

Cheers

 

Smiffy

[Smiffy]

You could try swapping the Pan and Tilt Stepper motors over. Not an easy job. IIRC they are both the same.

 

Cheers

 

Smiffy

[DrV]

Just possible that the two steppers are not aligned with each other i.e. when one of them is on phase 0 the other one is between phase 0 and phase 1. To correct it you have to power the unit up and, with the head stationary, you loosen one of the motor pulleys then tighten it up again. This allows the motors to match up.

 

HTH

Dave

[knightdan65]

Sorry to bring up this old thread again but I have now encountered a similar issue and am wondering what the resolution to this was?

[IRW]

Sorry to bring up this old thread again but I have now encountered a similar issue and am wondering what the resolution to this was?

 

You'll be lucky- the OP's three posts were on this thread, and they've not logged on since a few days after posting this 10 years ago...! Hopefully someone else will be along in the meantime who can help.

Edited April 22, 2021 by IRW

[gyro_gearloose]

If an otherwise perfectly working older Mac started having pan/tilt issues, I’d suspect the electronics if the mechanics all seem fine. I know from experience that the pan/tilt stepper motor driver circuit can develop faults with the current sensing resistors. Fixing those kinds of faults requires you to replace surface mount components, so I hope you’ve got a good soldering iron and a steady hand!

 

@knightdan - what problems are you having with your Macs? Do pan and tilt work at all, or only at slow speed? Given the age of your Macs problems can arise for any number of reasons, such as motors being worn out, wiring looms breaking, faulty motor drivers, or the optical sensors failing.

[knightdan65]

If an otherwise perfectly working older Mac started having pan/tilt issues, I'd suspect the electronics if the mechanics all seem fine. I know from experience that the pan/tilt stepper motor driver circuit can develop faults with the current sensing resistors. Fixing those kinds of faults requires you to replace surface mount components, so I hope you've got a good soldering iron and a steady hand!

 

@knightdan - what problems are you having with your Macs? Do pan and tilt work at all, or only at slow speed? Given the age of your Macs problems can arise for any number of reasons, such as motors being worn out, wiring looms breaking, faulty motor drivers, or the optical sensors failing.

 

Hi pal, thanks for the advice. Pan makes a nasty grinding noise but functions normally. Tilt is more problematic. At moderate to high speed it intermittently 'falls' as it gets towards its range limits as though the belts are slipping over the gears or the stepper motors are struggling. Belts and gears appear to be in good order. Martin have advised to replace belts and final pos switches as a first resort. Waiting for them to tell me if they have any left over at the bottom of their spare parts bin from ten years ago!

 

 

 

[gyro_gearloose]

Don’t bother getting your belts from Martin. They are a standard size/tooth profile, so you will be able to get them cheaper from engineering supply companies. These guys have probably got what you need.

 

Are you sure it’s a mechanical problem? If the motor drive circuit develops faults, the motor will still turn but it will have less torque. This will make the motor lose steps if it’s trying to move the head too quickly, and will sound like the belt is slipping.

[KevinE]

I would suspect the motor losing torque, proved by bobbing a known good motor in there.

[Brian]

On the '600 the motors are driven by the PBL3375 chips, which are in turn driven by the PBM3962s, which also control the drive current (=torque), which in turn receive a reference voltage from the main CPU. So it could be a wiring fault between the CPU board and the stepper board.

[gyro_gearloose]

The CPU, stepper motor drivers, and logic and motor power supplies are all on the same circuit board so the fault won't be with the wiring. The drive current is controlled by four sets of three resistors in parallel for both pan and tilt. If there is a fault with any of these resistors then the driver chip will supply less current to the motor resulting in a loss of torque.

 

To test your resistors you'll need to take the driver chip out of its socket and measure the resistance between ground and four other pins. There are four ground pins you can use (pins 5, 6, 17, and 18), and you'll need to measure the resistance from any one of these to pins 9, 10, 13, and 14. You should get about 0.5 Ohms. Anything higher than that means you have a problem.

 

This method only works for the pan and tilt circuits as they use the PBL3772N driver chip. All other stepper motors use the PBL3775 chip which has the same ground pins, but you only need to check the resistance to pins 2 and 21, which should be 2.2 Ohms.

 

Its well worth signing up to lightspares.com as they have part and circuit diagrams for all sorts of fixtures. They have the circuit diagram for both versions of Mac600s, for example, which will help you with troubleshooting your lights.