Neumann TLM170 problem

[RuudNL]

I have a problem with a Neumann TLM170 ("Circuit diagram 3")
When I apply phantom power, I hear a "whistle" and a lot of noise.
This sound disappears after a couple of seconds, that is: most of it.
What remains is a faint "beep" in the background.
The same situation occurs after switching the directional pattern.
I already checked the voltages coming from the DC/DC converter, but on the oscilloscope I do not see signs of a LF component.
Any ideas? It seems it is very hard to get the schematic diagram of the TLM170.

THIS is what it sounds like.

 

[djn111]

Hi,

If you ask me, send it to Sennheiser NL, have it repaired.

Invest some money to get it up to spec's again.

DJN

 

[micaddict]

Hi,

If you ask me, send it to Sennheiser NL, have it repaired.

Invest some money to get it up to spec's again.

DJN

Other than them having the correct schematic, I'd  say the techs there must be pretty talented indeed to do anything Ruud can't.

 

[RuudNL]

Found a schematic here, but unfortunately it is not very readable...

 

[Nyquist]

Ring and ask them to email you a copy.

 

[RuudNL]

I did (contact Neumann/Sennheiser), but they don't want to share the schematic...

 

[Moby]

Few weeks ago I tried to repair one 170 with similar simphtomes but withouth sucess. If u find the readable schemo please let me know, it will save one nice piece of gear.  ;D

 

[granger.frederic]

Dear Rud

did you try to replace the capsule with a 80PF capacitor, put the right power supply tensions from a external PSU (and bypass the built-in voltage multiplier), and inject a sinus wave at the Jfet input ?
then put a scope after the first stage , and second etc and see who is the culprit...
you could try also to measure the voltage across C1 and C2, to see if the capsule is well polarized...

cheers