Hello Roibeard, I have re-tested the flywheel diodes & have discovered a problem. 1 diode has a value of 1.119m ohms in one direction, switch the leads around & I get open circuit. I tested the other diode, I have a value of 97.3 K ohms in direction and 79.6 K ohms in the other. The book I have says test in 1k ohms range. The diode should test approximately 3k ohms in 1 direction & no continuity in the other direction.

I checked out all diodes... All ok. going to pull the batteries & check out the RAD's properly.

Morning Roibeard, Thank you for your explaination. I will double check the flywheel diodes and get back to you. Cheers.

CO refer to the drive transistors. Any transistor driving an inductive load requires a flyweel (flyback) diode to protect it from the high reverse voltage. A fundamental property of an inductor is to resist a change in current, which is exactly what happens when the transistor turns off. It uses the energy in it's magnetic field to try and maintain the current, so the faster the switching action the faster the change in current and hence the higher the back emf seen by the transistor ( e = -Ldi/dt ). The diode allows the current to circulate and dissipate the energy and clamps the voltage to approximately 1V (0.7V is the norm for a fully forward biased diode).
So if the flywheel diode goes open circuit the transistor will work for a short time (how long depends on the load and the magnitude of the reverse voltage).
So in summary always ensure the flywheel diode is OK before replacing the switching transistor. As best practice I always change both at the same time.

I forgot to mention, It keeps throwing up a CO code too