Next: Mag./Gun Fill. transistor PCB Up: Frequently Asked Questions: Elekta Previous: LV PSU Currents to
Every now and than the mag.fil. power supply has a bad mood. In old machines look for a bad rectifier. Replace it with a larger one. Look for bad Voltage Dependent Resistors over the rectifier. Replace the Darlington transistors (BTW42). Usually this helps.
We once had a machine that evaporated the transistors after approximately two minutes of warm up. It appeared that the magnetron filament had a short circuit. The resistance of a cold magnetron filament is very low. This resistance increases with increased filament temperature, reducing filament current. When the filament is short circuited the Magnetron-filament-current is not reduced, resulting in fire-works on the transistor PCB. It is a wonderful firework but you better stay out of the way.