I have an AVO 2 panel valve tester which I intend to clean and get working.

I have the circuit diagram and operating instructions. The Serial No. is
12372-147.



As I don't know if it is faulty or not I am proceding with caution.

At present I am checking the 'Meter unit' for correct operation before
plugging in the 'socket panel' as I don't want to damage the sensitive
moving coil meter movement.



The voltage outputs on the 9 pin socket on the side of the Meter box seem OK
(i.e. Anode, screen and heater)



I assumed that I could plug a 100kOhm resistor between the Cathode socket
(No.6) and a LT- heater socket (No.4) of the 9 pin socket and then push the
toggle switch sideways to check 'C INS' (cathode insulation).

However the meter needle does not move. If I turn the 'Set Zero' knob
anti-clockwise the needle vibrates and moves to the left.



I have cleaned and tested the contacts on the toggle switch. I have
soldered an IN4006 diode in series with the metal rectifier in case it was
faulty.

35 volts AC can be measured across the test resistor.



Am I wrong to expect the tester to measure this 'simulated faulty cathode
insulation'?



Furthermore, should I replace the 0.05microFarad paper capacitor with a
polypropylene version to improve reliability?



Any other tips would be greatly appreciated.



Regards,

Rudge