Neumann U77 repair

[cariocaman85]

Hi,

A (very good) friend of mine recently gave me a pair of non working Neumann U77, which I intend to repair... 

I have done some diy before (matachung C12, microphone-parts mods...) but any advice will be very very appreciated!


The first U77 has the following symptoms:

It sounds ok for several minutes, then no sound during 10/15 seconds, and the signal come back, then again, and again... I believe it might be a capsule problem related to moisture.


The second U77 produces no or very low sound, but microphonics noises are transmitted when I touch the body of the mike. Also the directivity selector is blocked on cardioid. It's only mechanical but maybe it has something to do with it.


I will post some exemples ASAP.

Any Idea of where to start?

Thanks,

Rémi

 

[abechap024]

Clean the pcb, look for intermittent connections and replace the electrolytic caps. Thats were I would start at least.

 

[cariocaman85]

Thanks,

I'll do that!

I noticed that the connection beetween the body and the capsule/headbasket part is not perfect. The head can move easily when I open the mic... Maybe I have to do something with the six pins that connect the headbasket to the body...

 

[soapfoot]

on the first one, give the capsule the "breath test." That will help let you know if your issues are capsule-related.

 

[cariocaman85]

Gosh, I just did the breath test and ...... FAIL!

When I breath on it, the sound cuts immediatly, I can hear some weird sounds in the background (probably capacitor charging).
30 seconds later the sound come back.

So now I know U77 n°1 has a capsule related problem, right?

Thanks for the advice!

 

[cariocaman85]

So What do you think it could be the best solution for U77 n°1?

-Cleanning the capsule myself? I'm not sure I can do that...

-Sending the mike for the capsule to be reskinned? To whom? I live in France...

-Mounting another capsule? I believe the U67 capsule from tskguy could match with the U77...

thanks,

 

[RuudNL]

I get the impression that this has to do with pollution on the capsule.
I have cleaned many capsules and most of the time the problems were gone after the cleaning.

 

[abechap024]

There are some good threads about cleaning your own capsules, and I tried it on some cheep chinese capsules and if you are slow, methodical and get the correct tools, its actually not as hard or dangerous as I thought. Still I dont know if I would start off cleaning a neumann...but very fixable!

 

[mad.ax]

Since you have a pair, I would start by swapping headbaskets, and/or capsule, in order to determine what's good and what's not...

If the capsule(s) needs to be reskinned: Siegfried Tiersch. He's the best (and not the most expensive 8). No silly expensive shipping or custom issues in your case, since he is in Germany.

Recapping is a good idea. All the lytics and the tantalum. On the U77 I fixed, I got rid of the tantalum. Changed C108 (coupling cap) for a Wima polypro. Tight fit but worth the trouble.
http://fr.farnell.com/wima/mkp2f033301m00kssd/condensateur-10-330nf-250v/dp/1890269.

Axel