AVO VCM MkII mains voltage check problem

[oceanobsession]

Hi bud , I'm still trying to figure these things out myself so I'm not much help , but i do have an original parts listing which is helpful , if you need anything checking i can look at mine if that helps , what did you replace the bobbin resisters with , cheers phil.     

[Bud Allen]

Right off if you don't have a clear and correct copy of the schematic, you have a problem. That was my biggest problem right off, that and AVO documentation is very poor, has many mistakes, and uses 50 words when 3 would do nicely.

Anyone having issues with any AVO tube/valve tester and has a good schematic should suspect poor solder joints as a possibility. Having found 13 cold and 1 that completely slipped off the terminal and left a hole in the solder behind, I now have voltages. One which messed up the bias, line mark, and V/ma was......the 'backing off' pot directly behind the front cover had one wire off the extreme terminal clockwise terminal, another poor solder joint, and that had an affect on the other circuits. To add to that the pot itself had no contact with the resistance on the last 2 or 3 degrees of rotation. Another pot had the last inch of the element flattened straight in order to stretch and make the tab connection, instead of hugging the roundness of the shell as expected ( in other words, the pot was resistance was no longer linear for the last part of the arc because the element was flat).

How on earth AVO let such out the door is a mystery

My advice to all is: Clean every pot and contact, and check all solder joints before you begin to trouble shoot the rats nest of wires and components. Assume nothing is good. Expect to readjust all voltages which have new diodes. The feedback from one component to the next means the component must be unsoldered to get a proper reading.

Many thanks to Gary.