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Author Topic: U87AI MT - rear diaphragm failure  (Read 1018 times)

Roald

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U87AI MT - rear diaphragm failure
« on: May 20, 2022, 10:08:57 AM »

Hi all,
I have come across an opportunity to purchase a set of AKG B-ULS and a Neumann U87 AI MT from late 80's / early 90's.

The Neumann only works in cardioid mode, as only one of the two diaphragms still work. Initially it was the rear one that still worked so a local repair shop switch the two diaphragms, so the faulty one now sits on the back side.

I was wondering if by looking at the photo's one could already asses if it's possible to salvage the one diaphragm... or if it's a total loss.
Many thanks in advance.

Kind regards from Antwerp, Belgium
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klaus

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Re: U87AI MT - rear diaphragm failure
« Reply #1 on: May 20, 2022, 12:17:43 PM »

Aside of moderate contamination, I don't see any damage to the capsule in the picture you provided.
What was the repair shop's exact diagnosis of failure?
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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

Roald

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Re: U87AI MT - rear diaphragm failure
« Reply #2 on: May 20, 2022, 01:15:55 PM »

Thanks Klaus. The shop did not find what’s wrong (they were not specialized in microphones etc). It was done when the mic was with the previous owner so I don’t know exactly what was discussed. You think it would rather be something in the circuit?
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RuudNL

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Re: U87AI MT - rear diaphragm failure
« Reply #3 on: May 21, 2022, 02:52:03 AM »

I suppose the cause of the problem could be in the switch assembly.
(More than once I encountered broken wires/connections.)
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klaus

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Re: U87AI MT - rear diaphragm failure
« Reply #4 on: May 21, 2022, 03:36:50 AM »

You think it would rather be something in the circuit?

Diagnosis whether it is a mechanical/capsule or electric/wiring problem is surprisingly simple and straight-forward:

Reverse the two wires that connect to the center of each diaphragm: switch and resolder the connection at the juncture where the yellow wires are soldered to the clear wires that disappear into the switch deck. Make sure to cover the diaphragms to prevent solder/flux splashes.

*If the dead side is now in front (in figure eight/omni patterns), it's most likely a wiring issue, and a simple ohm-meter test will reveal where the open connection is located.

* if the dead side remains in the rear (which is now the cardioid position), the problem lies with the capsule itself.


In either case, solving this is not rocket science - at reasonable cost, if any.
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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

RadarDoug2

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Re: U87AI MT - rear diaphragm failure
« Reply #5 on: May 21, 2022, 05:00:05 PM »

Klaus, I think you got that backwards!
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klaus

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Re: U87AI MT - rear diaphragm failure
« Reply #6 on: May 21, 2022, 05:09:15 PM »

Please explain what I got backwards. I am pretty sure that the reversals as described will reveal the issue.

As the capsule's physical orientation in the head stays put, despite the reversal of the electric lead outs, a physical defect will therefore remain with the same (rear) side.
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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

Kai

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Re: U87AI MT - rear diaphragm failure
« Reply #7 on: May 24, 2022, 12:27:04 AM »

Please explain what I got backwards. I am pretty sure that the reversals as described will reveal the issue.
...
Funny, I too thought you reversed the assignment on first read, reading again in the light of your reply I did understand.

Your explanation is from the mic housing’s point of view, not the capsule side’s.
Should be clear and logical, but my first idea was different too.


Maybe a sentence like “if the error follows the capsule side it’s a capsule fault” would read more intuitive.
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RadarDoug2

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Re: U87AI MT - rear diaphragm failure
« Reply #8 on: May 24, 2022, 04:52:37 PM »

Ah, I see what you are saying now. Shows how the simplest things can sometimes still be clear as mud.
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