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

 

[nyc_jimmy]

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...)

Hi Ruud,

I'm having some issues with my M16-II but can't find the schematic anywhere.
Would you be able to share it by any chance?
Thank you in advance.

 

[Khron]

Hi Ruud,

I'm having some issues with my M16-II but can't find the schematic anywhere.
Would you be able to share it by any chance?
Thank you in advance.

Post internal photos of both sides of the board(s)?

 

[RuudNL]

What is the problem with this microphone? It is really a very simple circuit.

 

[nyc_jimmy]

A client dropped it in the studio and the wires that are soldered to the jack came loose. We just need to know which pins they get soldered to.

 

[nyc_jimmy]

I'd really appreciate it if anyone could please share the schematic, thanks again.

 

[nyc_jimmy]

Someone had asked for a pic. We're not exactly sure where some of those wires need to go.
We called Telefunken twice but unfortunately they were helpless. If anyone could please share the schematic I'd really appreciate it.

 

[Khron]

Someone had asked for a pic.

Someone please tell me that electrical tape there is not stock from the factory...

 

[hazmatstrat]

Pin1: B+ usually Red 120 to 140vdc Pin2: Heater usually Yellow 6.3v Pin3: Pattern usually Blue 0 to 120vdc Pin4 &7: Ground Pin 5&6: Audio. possibly black and green These will come from the transformer. Trace the wires to the transformer to find the colors. You may need to connect the audio wires and listen to the mic to check phase.

 

[nyc_jimmy]

Pin1: B+ usually Red 120 to 140vdc Pin2: Heater usually Yellow 6.3v Pin3: Pattern usually Blue 0 to 120vdc Pin4 &7: Ground Pin 5&6: Audio. possibly black and green These will come from the transformer. Trace the wires to the transformer to find the colors. You may need to connect the audio wires and listen to the mic to check phase.

Thank you very much.