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Roboscan 918 Tilt problem

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Hopefully someone will be able to point me in the right direction on this little problem I have.


I have a Roboscan Pro 918 with a issue with the tilt stepper circuit.


Symptom :-

The tilt motor has no strength will hold if assisted by hand but soon as you change the channel value for a slightly different tilt angle it drops


Solutions tried :-

New genuine martin stepper motor - exactly the same


New Driver chip - exactly the same


Swopping connectors with Pan circuit works fine


Have checked the board with a multi-meter and located 2 resistors connected in series on pin 2 (I think-board is at work on the bench) of the 3771 they are marked 3R30 (3.3 Ohms) the meter is showing 500 ohms on each which makes me think it's strange for 2 resistors to fail to the same value right next to each other.


Any help would be greatly received or suggestions on what to try next



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Hi Matt,


If you swap the pan and tilt connections around on the pcb and the motor will work fine on the PAN output then the problem will lay on the tilt output on the main PCB.


You say you have changed the driver chip so the problem will lay on the resistors around the driver chip on the main PCB.


The resistors are 3K3 ohms but there's 3 in parallel and they will meter in at around 600ohms so this is fine.


There is 2 banks of these 3 resistors, 1 lot on pin 2 and another lot on pin 21 too..... Try locating these lot too and measure these out and see if they have gone open circuit.....If they have they will cause the symtoms you decribe. The ones on pin 21 are R562, R563 and R564


Hopefully this will be your problem

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