U87 repair (pics inside)

[abecedarian]

I have an U87 from a studio.  It didn't work. They gave it to me. The capsule appears fine. The top part doesn't tighten onto the body and it passes no sound. What recommendations are there for people/companies who modify/fix/repair U87 mics?

 

[Mike Cleaver]

Where are you located?
There are a number of good people in Europe and the US who can work on these mics.
Neumann is a good place to start, both in Europe and the US.
There are a number of specialists who fix and modify Neumann mics as well.

 

[abecedarian]

Palm Beach, FL.

 

[bruno2000]

Sennheiser USA
(860) 434-9190

 

[abecedarian]

Wiggled the top after taking it apart and got it to work for a while.  It sounds like a simple connection problem.  Weird thing is, this U87 sounds freaking amazing. I recorded it into Logic and listened back. Unlike the (1998) other one I had.  This is way creamier!!! A quick search renders this one circa 1980-81.  I'm smiling from ear to ear.  Santa came early. It does not have the letters "A" or "I" on it any where.  Written on the black ring is "Type U87 P48 Made In Germany Neumann - Microphone". Inside there is "circuit diagram 21" written on a sticker.  The capsule bottom says "KK 87 A 19173." Does this problem sound to you like something I can tackle or should I still send it in?

 

[Stagefright13]

WOW a free 87?? They all sound great. I think th AI ones are crisper tho cause no 20 years of cigarette smoke. But all of them are great!

John

 

[abecedarian]

Listening back to the recording, I hear a faint low end hum in the background. 

 

[maxwall]

check the 2436 FET, or one of the tant caps has shorted or opened.

 

[abecedarian]

OK I will.  I want to look at the capsule. Is this dangerous? Looks like just a few screws to take the top cover off. If I can't fix it and i send it for repair, I want to know I'm getting the same capsule back. 

 

[Mike Cleaver]

Be very careful if you remove the head grill.
You can easily damage the pattern and pad switches.
Send it to Neumann in the states.
You don't want to damage the capsule either.

 

[Gus]

There is a method to opening up the headbasket.  The switches need to be in a certain position not the break the pins.

http://www.neumann.com/forums/view.php?bn=neumann_mictec&key=1282685534&v=f

http://recforums.prosoundweb.com/index.php/m/366800/0/?srch=opening+u87+headbasket#msg_366800

 

[abecedarian]

It looks not too bad for being used in a pro studio since circa 1980.  Notice the chip of gold pulled back.  There is dust on the diaphram (more on one side than the other naturally) but does this look to you guys as something that should be cleaned?  The way the basket sits on the body feels weird. Notice the bottom of the capsule housing - the pin sockets 2 and 5 look like part of the metal is missing. Maybe that's why the wiggling gets it to work for a while.  I can tell someone tried to fix this issue by bending one of the legs a tad to make a better contact.  Also is the way the capsule is leaning back or tilted a normal thing from factory? Now to try to tackle to low hum.  

 

[Biasrocks]

I would leave the capsule alone, it doesn't look too bad all things considered. If you really want to clean it I would suggest seeking out a pro to do so.

Looking at the pins in the above photo, it looks like Pin 5 and Pin 2 are buggered. Try taking a dental pick or a small screwdriver and gently retension the sockets so that the pins fit snuggly. See if you can find the rest of Pin 5/2 in there, you might be able to rescue it. Make them all look nice and shot of deoxit in the Pins may help as well, but you need to retention the sockets first.

Also, the 10uf/63v electrolytic off the biasing resistor (R11) is not the proper value. According to the schematic, this should be at least 20uf. Subbing a 22uf/10V part is appropriate. This is probably not the main issue, but I thought I'd point it out.

It also appears that your mic was originally setup for 50 ohms, you should convert this to 200 ohms by restrapping the output transformer. It looks like the output pads have been removed, so this may have already been addressed by the previous owner, but worth verifying.

If you're not comfortable doing this, I would send it back to Senheisser and let them do their magic.

Mark

 

[Gus]

As Biasrocks posted pins 2 an5 look like they need work.  If you take the plastic base apart to work on the connector do it over a pan hopefully you will not lose the parts inside

I have not seen inside this version battery u87.  Note the transistor to the left of the 10uf/63VDC cap that cap might be part of the voltage dropping regulation section so I would leave it alone.  It looks like there is a blue tant to the left of the source resistor I would guess that is the source resistor bypass cap.

What I would do with the capsule is get a clean optic brush and very very gently remove the dust from the clear edge part of the diaphragm.
If you apply water you really need to know what you are doing,  The gold can lift right up after the capsule has a few decades of use it can be cleaned but it is tricky.  The peeled gold section makes me believe this capsules gold is not adhering well.

 

[abecedarian]

Thank you, guys. I played with the pin sockets and got it to work for a while but putting the mic back together made it not work again.  I noticed the XLR plug wiggles too.  I didn't notice that before. I guess over the years people were trying to get it to work by wiggling causing things to get loose.  BTW, No one mentioned the missing screws in the pics of the Capsule? Did they leave them out intentionally in the diaphragm tensioning ring on purpose?  And there are two holes on the side of the capsule too unused.  

 

[abecedarian]

I contacted the defunct studios head engineer where I got this mic from.  It turns out this mic was the one they sent in to Korby Audio in Nashville for modification - long before he started his own brand. http://www.korbyaudio.com/  No wonder it sounds so good. The engineer told me "you have a very special microphone... Of course *&^*@ was clueless about the mod I did to the equipment we had. That Mic will sell from 3 g's easy maybe more. Its a keeper and worth fixing". This story just gets better and better. Contacting them now.  I feel better knowing this because from what Ive read, Neumann/Sennheisser wont touch modded mics.  And they aren't cheap when it comes to repairing either. 

 

[Biasrocks]

Well.....

The electronics look pretty much stock to me and the capsule is definitely untouched, missing screws and all.

As I said before the mic was originally strapped for 50 ohms instead of 200 ohms and had an output pad installed. It looks as if the pad was removed at some point and most likely was changed to the 200 ohm strapping on the transformer.  The 10uf/63v electrolytic is an ill advised modification and should be brought back to stock value.

Perhaps these are the famous Korby mods?

Mark

 

[zebra50]

It doesn't look to me as though there are any screws missing. They are just clearance holes for the screws from the other side.

 

[Biasrocks]

Agreed, you can see the lacquer coating that they place over the screws covering the cavity.

Mark

 

[abecedarian]

Even with the low end hum in the back ground, this U87 sounds way better than any I've sung into before. I'll ask Korby about that cap.