Mac250 pan problems

[Jfa]

Hi All,

 

I seem to have exhausted my searching and I'm stuck with a problem.

 

I've got a mac 250 (old style) and it has a Feedback error on the pan. I've cross changed the sensor with a working mac250 and that's fine, the wiring looms to both sensor and motor power are fine too. When I turn the mac on and the pan motor kicks in it is very juddery and dosn't want to run smoothly. I then removed the motor and checked it on another working mac and it ran smoothly.

 

Has anyone got any ideas or have seen this problem before? I'm wondering if it's something to do with the PCB controling the pan motor?

 

Thanks very much

 

J

[maxjones2000]

Could be a bad pan driver chip... maybe try swapping the card with a known working one, and see if that fixes it. Or see if the problem follows the card http://www.blue-room.org.uk/public/style_emoticons/default/smile.gif

[gyro_gearloose]

If it isn't the driver chip, then it will be the resistors used by the driver chip to determine the current across the motor. There are sets of three 1.5Ohm resistors in parallel, two per driver as I recall, which will eventually fail. This means that the chip is not detecting the current across the motors coils correctly. This in turn means that the chip allows too little current to flow which reduces the torque of the motor.

 

This is a very common fault, and a little bit of a pain to fix as you have to cut parts of the chip holder to get to some of the resistors. If you can squeeze them in then higher Wattage 0.5Ohm axial-leaded resistors are a better fix. A 0.5 Ohm axial resistor is used as that is the same resistance as three 1.5Ohm resistors in parallel.

 

Hope all this helps