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Author Topic: Broken pins on the head of an old u87  (Read 941 times)

mikezietsman

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Broken pins on the head of an old u87
« on: March 22, 2019, 06:06:53 pm »

I recently found a u87 in rather poor shape but described by a non-technical but competent associate as ‘working fine in Cardiod but buzzing in other patterns’

Upon closer inspection of his photos I see that two of the pins in the head assembly seam to have either snapped or been pulled out.
(Pins 1 and 2 - in the attached picture)

Is this the sort of thing that might be fixable without purchasing a very expensive new head assembly?


Does neumann sell just the plastic portion of the head assembly which houses the pins? I don’t need the grill or the capsule. Does anyone know the part number offhand?

*Edit*

I have just found the part number and corresponding price for the replacement: 060737 - rather steep for what it is but understandable given it’s rather unique usage. Has anybody got any hints for work arounds I could use to repair the part?

*Second Edit*
I have purchased the mic - I am not looking for advice on whether to purchase or not. Just wondering if two snapped pins will cost me 377 GBP or if anyone could offer a work around.
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klaus

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Re: Broken pins on the head of an old u87
« Reply #1 on: March 22, 2019, 08:52:20 pm »

You can reassign #1 and #2 pins:
#7 is ground and not really necessary (original K67 don't have it), and you could use pin #6 (low end cut, which in its stock configuration is rather useless because it cuts a tremendous amount of low end when engaged. It will take some rerouting of wires, but if you download a schematic (http://recordinghacks.com/microphones/Neumann/U-87) you should be fine.

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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

mikezietsman

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Re: Broken pins on the head of an old u87
« Reply #2 on: March 24, 2019, 09:18:03 am »

Thanks Klaus, that is incredibly useful info. Once I get the mic in person I will mull over solutions. I would rather leave the mic "stock" but It is good to know that work- arounds are an option!
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klaus

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Re: Broken pins on the head of an old u87
« Reply #3 on: March 24, 2019, 12:24:21 pm »

I should have added that you cannot replace individual pins; at least, I have not been able to:

Transplanting a pin from another head, or fabricating home-made copies usually fails, because of the heat required to solder them to the remaining stump: the plastic in which the the original pin is encased, melts. Likewise, removing the stump and gluing a new pin is labor intensive and needs some experience.

But if anyone has found a better, simpler way to deal with a broken head pin, let us know!
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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

mikezietsman

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Re: Broken pins on the head of an old u87
« Reply #4 on: March 24, 2019, 03:03:27 pm »

I see. Then you followed my train of thought with very little to go on haha.

I was thinking to attempt a pin replacement using a narrower pin and some epoxy. With experiments first being done on a much more broken plastic head which I have in my possession.

Do you know if Neumann sells a less complete version of that mounting assembly for a lower price?
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klaus

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Re: Broken pins on the head of an old u87
« Reply #5 on: March 24, 2019, 06:37:04 pm »

Neumann only sells the complete head assembly which does not include any of the original U87's high-impedance head components.
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Klaus Heyne
German Masterworks®
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Kai

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Re: Broken pins on the head of an old u87
« Reply #6 on: March 25, 2019, 06:40:29 am »

I should have added that you cannot replace individual pins; at least, I have not been able to:

Transplanting a pin from another head, or fabricating home-made copies usually fails, because of the heat required to solder them to the remaining stump: the plastic in which the the original pin is encased, melts. Likewise, removing the stump and gluing a new pin is labor intensive and needs some experience.

But if anyone has found a better, simpler way to deal with a broken head pin, let us know!
The summary and essence of my lengthy post below:
Use water for cooling the plastic while working on it.

---

In detail:

 I had the problem of soldering parts that are stuck into plastic several times, so I developed a simple way of dealing with it.

There are two possible ways to work around the broken pins, both would use the same basic approach:

First you have to unmount (Klaus's instruction see below) and desolder everything from the bottom plate where the pins are stuck in (make a photo to later know which wire goes where).
Do not heat up the connections for more than a few seconds while doing so, or the plastic will melt and the pins will come loose.

Next place the plate into a platter filled with water and using tissue soaked with water to cover the top of the plastic except leaving a very tiny area around the pin you're going to work on.


Now you have two options, either completely replace the pin or soldering an extension just on top of what's still there.
Soldering on top is easier, but will not make a very strong mechanical connections so it will easily break. This might be sufficient if you do not remove the microphone's head on a regular basis.

If you are going to solder on top, clean up and scratch the remains until you see pure metal.
Then pre-tin this area using high quality solder, a relatively hot iron (380°C) and a short soldering time.
Do this until you are sure the solder has really connected to the brass metal, not just being glued to it.
You might need to repeat the cleaning if the first attempt was not successful.
Now you can solder the pre-tinned replacement pin on top.
Always keep the working area's close surroundings wet to avoid melting the plastic.
.
.
The second and more professional way is, to drill out the remains of the old pin with a tiny drill.
It might be possible that you can pull out the remains once you removed the collar that holds the pin in place using a 2mm drill or a grinder.

If not, you have to drill very straight and very centered through the original, starting with a new sharp tiny drill 1mm or smaller.
In a second step drill just big enough to fit the replacement pin.

Doing so will heat up everything, so cooling like mentioned above is absolutely necessary. This time it's easy: just do it completely under water.

The replacement pin needs to have a working diameter of exactly 1.5 mm, anything smaller will not make reliable contact. There are a lot of connectors out there using this sized pins.

When everything is done, cover the serial number with plastic tape, then wash the plate with a mix of distilled water and pure alcohol, (whiskey won't do ;D ) dry and remount.


---

Here is a copy of Klaus's instructions how to dismount the basic plate:

The three large slot screws that hold the head assembly in the grill need to come all the way out. Place the head upside down (contact pins at top)

What is absolutely essential for removal:
BOTH ATTENUATOR SWITCHES MUST BE IN THE 'OFF' POSITION. If even one is not, the assembly will not clear the basket!

After removal of the screws, the best way to clear the nipples of the roll-off switches past the viewing windows in the head grill without breaking them off is to:

1.without trying to pull the head assembly out, slightly tilt it forward inside the grill (capsule moves toward the front of the grill)

2. grab the head assembly by the pins and lift up at the front only, until the purple pattern selector switch plate has cleared the grill completely

3. move the head assembly as far to the front of the grill (pattern selector = front) as possible.
This will be just enough clearance for the rear nipples to clear the grill

4. keeping the head assembly slightly tilted vis a vis the grill, lift it up and out. (Try not to tilt the capsule assembly so much that it can scrape the rim of the grill.)

Reassembly is in reverse.

P.S.: Never loosen the smaller brass slot screws located toward the center on the bottom of the head assembly: These affix the various switches inside the head assembly and the assembly's cover.
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klaus

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Re: Broken pins on the head of an old u87
« Reply #7 on: March 25, 2019, 10:22:26 am »

Thanks, Kai. Very thorough.

What you still might cover in your method #2:
 
* how the new pin is secured in the plastic (glue?)
* how a smaller diameter replacement pin will make sufficient contact with the original (larger
   diameter) female counterpart in the mic's amp
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Klaus Heyne
German Masterworks®
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Kai

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Re: Broken pins on the head of an old u87
« Reply #8 on: March 25, 2019, 03:09:10 pm »

Best if the new pin is selected for a tight fit.
A bit of epoxy glue will do the rest if necessary.
Once it's soldered on the back, the pin cannot fall out anyway.

The new pin should have exactly 1.5mm working diameter.
Else it will NOT make reliable contact if it's smaller, or if it's bigger, it will bend the contacts in the "bottle", so it will no longer work with another head.

There are lots of connectors out there that can serve as donor.
Use one where the pins have a collar on the outside.
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mikezietsman

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Re: Broken pins on the head of an old u87
« Reply #9 on: March 26, 2019, 07:35:11 am »

This is gold. Thank you Kai and Klaus!

I now have multiple solutions (which I can try)
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klaus

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Re: Broken pins on the head of an old u87
« Reply #10 on: March 28, 2019, 05:49:57 pm »

Kai,
Can you check your messages. please?
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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com
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