With the rotor powered up and connected to the rotor, measure the voltage at
pins 1 & 3 on the Molex (or Jones) connector on the back of the control box.
It should be 6 volts. When you rotate, the voltage at pins 2 and 3 should
If there is no 6 volts, first check the connector. The Molex pins on the
cable half have a tendency to work their way out sometimes. Inside the control
box there is a 7806 voltage source and a 15 ohm, 3 watt dropping resistor right
on the top of the control box when you remove the cover. Check those
directly with respect to chassis.
If there is 6 volts, but no varying voltage on pin 2, the problem is either
the rotor cable, the Cannon plug at the rotor, or the position pot inside the
If you do have a varying voltage on pin 2, open the control box and measure
the voltage across the motor that drives the indicator. If it has voltage on
it, the brushes are probably bad. If it does not, check the D1 bridge diode
across the 13 volt, center tap portion of the secondary of the power
transformer. It, along with two voltage regulators (pass transistor Q5, zener
for the pos side and pass transistor Q6, zener diode D5 for the neg side),
supply the split voltages needed by the comparator Q7 which drive the motor.
Hope this helps.
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