Neumann TLM170i dc-converter problems

[Bo Hansen]

I have a problem with a Neumann TLM170i, the oldest discreet built version. (not the R version with thick film circuits)
I have an fault on dc-converter board, where there is a short circuit in one winding of the small ferroxcube transformer.

I have spoken with the very helpful Martin Schneider on Neumann's forum, but there are no spare parts left to buy for this old TLM170i version.

Unfortunately I can not get hold of a schematic or winding data on ferroxcube transformer, and then it becomes difficult to make a new one.

Is there anyone here who have solved similar problems with dc-converter board, and figured out how this transformer is built in its winding structure.

Maybe someone even has a dc-converter card or transformer for sale as a spare.

I'm also looking for a schematic of the TLM170i version.
(Neumann would unfortunately not give out schematic of this particular version)
But maybe there is someone who has re-drawn the electronics more or less complete, but still can give me an idea of how the design looks.

Bo

 

[gyraf]

Wouldn't it be possible to reverse-engineer the existing coil/transformer - taking it apart and counting windings?

...attached the sadly primitive schematic I have...

Jakob E.

 

[Bo Hansen]

Thanks Jakob,

Sure, I've thought about this.

Had it been a normal dc-converter coil/transformer I would have given me a try, but this particular transformer has numerous outlets and also extremely thin wire.

So the risk is that it only gets a lot of small bits left from the wire when I try to wrap it up.

Bo

 

[RuudNL]

Just a wild guess, but wouldn't they use the same transformer as in the U87Ai ?

 

[Bo Hansen]

RuudNL,

I think you mean the latest version U87Ai, that uses the U89 dc-converter card.

But unfortunately, although this dc converter has many positive and negative voltages for polarization switching, it is a simple oscillator constructed with a choke that has an extra coil tapping.

But perhaps there are other microphones with a more complex ferroxcube transformer similar to TLM170 dc-converter design.

--Bo

 

[chefducuisine]

Bo,

I've got the same problem.
I did already remove the hot glue that is around the coil as well as on all it's related solder joints.
Silly me - I destroyed the tiny wires... should have heaten it up first... :-[
Therefore please do not remove the glue yet!!! It would be helpfull to do some measurements on the working inductors.
Are you able to do some inductance measurements on the remaining intact coils?

I ordered a replacement board from Neumann - almost 600 EUR later I discovered it is the one for the 'R' Version; not usable.  :'(
BTW This one didn't help either:
www.neumann.com/download.php?download=info0061.PDF


This means I will have to find out how to get the new board to work or reverse engineer the coil as far as possible - but then I still don't know where to connect all the outlets... If I understand the purpose of the circuit correctly all it does is creating the various voltages -out of the phantom power the most efficient way- for the different patterns as selected by the switch on the back of the microphone.
The tiny wire would not be a problem - I have access to a supplier and can provide some.
To get some more understanding of the circuit It would help to draw up a schematic.
Hopefully I can start with that in a few weeks when I am back home...

Best regards,
Chris

 

[Bo Hansen]

Chris,

I have also discussed my problem on Klaus Heyne's Mic Lab forum, and with their help I have been able to proceed with troubleshooting.

http://repforums.prosoundweb.com/index.php/topic,36292.0.html

Visit the forum and share the information.

--Bo