damaged M7 capsule

[AErige]

Hi everybody,
some time ago I bought a M7 for a u47 mic that ended up with a k47 capsule.
Over the past few years it's been laying down in its box.
I'm currently building a u47fet mic and wanted to try it.

One diaphragme looks ok and measures around 70pF.
The other one looks damaged (see pic) and measures way out of specs : 300pF
Since M7 doesn't have a clamping ring  to protect the diaphragme when laying down...I guess the central terminal wire wasn't enough to handle the capsule weight and the membrane collapsed (yet its kinda weird cause there are some cotton layer at the bottom) .
Is there a way to fix this ?

 

[OPR]

It looks like the diaphragm is stuck to the backplate.
You could try slightly loosening the center termination screw to let some air in to equalize the pressure. hopefully it will release.

 

[zamproject]

Hello

I confirm that diaphragm is stuck to backplate  :-\
but pressure is usually compensated with a small hole at the side of the backplane, so there is chance loosening the screw won't help...
I have this problem once, I fix it by removing the screw and using a small and soft tool to pull a little the diaphragm, you have to be very very soft...
It happend a second time and I rip it, so the chance is 50/50...
As the diaphragm was dead I removed it entirely and was able to see that back plate was not properly cleaned, some grease was visible, probably remaining from metal work 
Sorry I'm not optimistic in your case which look exactly the same as me 3 or 4 years ago.

Best
Zam

 

[AErige]

thx for your advices, guys 

I tried loosening the screw then removing it but diaphragm is still stuck  :'(

I'm gonna try to pull it very softly with a strand of hair ( or a tiny paintbrush  maybe)
Won't it be a problem for the good working diaphragm if I rip the other membrane (pressure wise) ?

 

[e.oelberg]

you could try polarizing it up to 80 volts till the complete membrane gets sucked in. When you switch off the polarization, the release of tension might lift the complete membrane off the backplate

 

[12afael]

it can be crazy but I can imagine some alternatives to introduce something inside the capsule. Maybe some kind of vacuum or blower could be used or even loud soundwaves. they should be better alternatives I think.

 

[AErige]

just to let you guys know ...
I succeeded  to pull it very softly with a toothpick ( 000 paintbrush was too  flexible).

Unfortunately diaphragm  got stuck again as soon as I removed the tool.
So either it is dirt/grease/body oil behind diaphragm (because of the little bubbles on top of that imprint you can see in pic) or wrong glue that let membrane's tension loose  over time... 

zamproject had same issue with chuckD 's M7
https://groupdiy.com/index.php?topic=52514.0

 

[zamproject]

just to let you guys know ...
I succeeded  to pull it very softly with a toothpick ( 000 paintbrush was too  flexible).

Unfortunately diaphragm  got stuck again as soon as I removed the tool.
So either it is dirt/grease/body oil behind diaphragm (because of the little bubbles on top of that imprint you can see in pic) or wrong glue that let membrane's tension loose  over time... 

zamproject had same issue with chuckD 's M7
https://groupdiy.com/index.php?topic=52514.0

What I say previously... have same problem...dirt and grease... and of course I see you have a Chuck M7, but not naming to not harm the guy.
By that time I was not happy at all how he handle my problem which is clearly the result of a bad work... but you can only see that if you remove the diaphragm.
Anyway...
Your capsule is dead, need a reskin with absolute meticulous backplane cleaning.
I still have the one replacement capsule he send me (for two dead ones...) which still fine IIRC last time I look at it.

I forget all this and buy two thiersch time ago.

Best
Zam

 

[Banzai]

Why not just use as is? Only need one side for a 47 FET.

 

[rmburrow]

What I say previously... have same problem...dirt and grease... and of course I see you have a Chuck M7, but not naming to not harm the guy.
By that time I was not happy at all how he handle my problem which is clearly the result of a bad work... but you can only see that if you remove the diaphragm.
Anyway...
Your capsule is dead, need a reskin with absolute meticulous backplane cleaning.
I still have the one replacement capsule he send me (for two dead ones...) which still fine IIRC last time I look at it.

I forget all this and buy two thiersch time ago.

Best
Zam

Get the capsule reskinned or replaced.  You may be able to buy a M7 capsule.  I have no idea how much Mr. Thiersch charges to reskin a capsule.  That capsule was done the moment the other tech disassembled it.  During assembly, the membrane is clamped on under tension.  For a pressure gradient (dual membrane) capsule, the tension on the membrane must be the same for both sides.  Cleaning a capsule is of dubious value; I went through that a while back; eventually both capsules were replaced (a stereo mic).

Windscreen use is a lot cheaper than replacing capsules.  Talent won't use a windscreen and won't pay upfront $1500 US to replace capsule, they get a EV RE20 or a Sennheiser MD421...lol

Off the subject, does anyone know what Mr. Thiersch charges to replace a nickel membrane in a Schoeps M934?

 

[zamproject]

Get the capsule reskinned or replaced.  You may be able to buy a M7 capsule.  I have no idea how much Mr. Thiersch charges to reskin a capsule.  That capsule was done the moment the other tech disassembled it.  During assembly, the membrane is clamped on under tension.  For a pressure gradient (dual membrane) capsule, the tension on the membrane must be the same for both sides.  Cleaning a capsule is of dubious value; I went through that a while back; eventually both capsules were replaced (a stereo mic).

Windscreen use is a lot cheaper than replacing capsules.  Talent won't use a windscreen and won't pay upfront $1500 US to replace capsule, they get a EV RE20 or a Sennheiser MD421...lol

Off the subject, does anyone know what Mr. Thiersch charges to replace a nickel membrane in a Schoeps M934?

Hello, not sure you get the point, but I can misunderstand what you say
This is not a dirty membrane/diaphragm, this is a dirty backplane, not well cleaned before diaphragm assembly !
You can't clean it without removing the diaphragm, you can see at OP pictures the trace and deformations due to some remaining shavings from metalwork, and the diaphragm get stuck because of remaining grease  :-\

Anti-pop / windscreen, used or not, can't help prevent this.

I don't remember the reskining price from Thiersch, but I remember that flat reskin price was about half a new M7 from him. Considering my faulty ones need more than a reskin simple work I give up and buy new...

Best
Zam

 

[ln76d]

134euro for whole capsule reskin with PVC, PET 112euro if prices didn't rise.