Strange Telefunken M16-II microphone problem

[RuudNL]

Today I got a microphone for repair from a client who said that the microphone only worked in the cardioid setting.
As soon as he changed the pattern setting on the power supply, the microphone stopped working.
I have attached a part of the schematic in the attachment.
Can you spot was is wrong here? (Everything looked original, pretty sloppy build quality by the way...)

 

[MicUlli]

Did you measure voltage via C1 ?

 

[RuudNL]

Did you measure voltage via C1 ?

Voltage over C1 is about 60 volts.

 

[Khron]

100M & 47nF creating a long time constant (4.7sec to reach 63% of the change)?

 

[RuudNL]

100M & 47nF creating a long time constant (4.7sec to reach 63% of the change)?

You just answered the 100.000 dollar question!
Of course 47 nF is a ridiculous value, usually you will see 1000 pF here.
When switching from cardioid to omni you will get -30 Volt on the grid and when you switch to figure-8 the result will be +30 Volt on the grid., totally disturbing the bias setting of the tube. Let's hope that this was a mistake and that the 47 nF is not a standard value in this microphone. I have changed the 47 nF for a 1 nF capacitor and now the pattern switching works as expected.
And what is more important: the microphone does no longer cut the output after pattern switching!

 

[MicUlli]

Perfect

 

[Khron]

You just answered the 100.000 dollar question!

So where's my money then? xD