Beyerdynamic mc930 SDC repair

[Lowfreq]

Hey all,

I've had a pair of mc930s that I've used for the best part of a decade now, and one of them has started to lose volume compared to the other. I've attached a pic from tests of sending pink noise to the mics to show the difference.

They've been well looked after, with no real knocks that I can recall, and stored in a nice dry environment.
Tonewise, both mics still sound the same, so I don't know if I'm safe in assuming the capsule is still good.

I checked that I was getting signal on both pin 2 & 3 of the mic going into my preamps, thinking that I could've had a bad sold joint losing half of the balanced signal, but I'm still getting signal on both pin 2 & 3, but still considerably less than the good mic.
I even swapped the pcb into the other mic, and the problem followed the pcb.

I gave the connector to the capsule, and the hi impedance are a good clean with isopropyl, and that suddenly made the mic work again perfectly, but for only 10 minutes.
It then made a popping, rumbling sound and then I was back to where I started with low output on the mic again. 

Maybe I could send it to be fixed somewhere, but here in New Zealand our options are limited (and expensive).

I have the service manual which has the schematic, but it looks like a lot of the parts they used are now obsolete.
I've built a few tube mics, but I haven't really dived into sdc or fets at all yet (let alone smd components), since what I already had worked until recently.

Has anyone dealt with one of these before? It's the working for 10 mins and then popping and rumbling back into a broken mic that's baffling me.

Steve

 

[emrr]

That sounds like a connection problem to me.  I think of a mic I have with a body that completes the ground path, some of it screws together and it sometimes requires adjustment of the screw on grill to get full level without noise.  Consider any areas that might occur. 

 

[Khron]

Makes me wonder how different the circuitry is from the MC830 / Opus 83. I bought one with some issues (iirc) a while ago, which came good after a couple of capacitor replacements.

 

[Lowfreq]

Apart from cleaning it, I’ve focused on the receptacle that connects to the capsule. (Pic attached) It seems quite flexible, which could be hindering it making a good connection. It could be flexing before it locks in to the capsule pin.

The capsule seems fixed with the mc930 so I can’t unscrew it or attack the problem from the top, so it’s been more about guestimate of lining up the receptacle before sliding the pcb back in.

I’ve shifted it’s positions a little bit with a small screwdriver a couple of times. At one stage we seemed to be fading between full volume and broken volume every 20 seconds or so.

At the moment I’ve got it where I think the connection is good.
It’s been on all afternoon, and it’s had no volume drops at all. I don’t know if I’m confident enough to use it on a session yet though.

I’ve double checked screws to the body, and I’m getting good continuity there.

It’ll be interesting to turn it back on tomorrow and see if both mics are still behaving themselves.

 

[phonofranz]

Did you solve the noise in the end?
My experience with mc930s is quite frustrating and related to similar issues.

I've got a couple from Thomann in 2017 and was really pleased with sound and lack of noise. One out of two suddenly started crackling/popping and being noisy after a year or so. Thomann asked for some recording proving the issue and then Beyerdynamic swapped it with a new one under warranty and re-tested the other one too (got two new frequency plots and sens tests).

In 2019 I got the same issues again with the new microphone, the one that has been swapped. Again: they've swapped it with a new one and re-tested the other. This time they didn't asked me for any proof of the issue, they just approved the RMA and send me the pre-paid post in no time.
I was pissed for the double fault but pleased with the service from Thomann and Beyerdynamic, even if they made me think they had a few returns.

Now: yesterday again the other microphone, the one that never acted up before, got extremely noisy, a pink/brown broad noise without crackling. Two years from the last swap has passed and I guess they won't respond this time (I will try tomorrow tho).

I've opened the mic and checked for screws/chassis contact with pin 1. Checked/cleaned capsule connection. Noise still there unchanged.

EDIT: I've just noticed that the noise floor keep the same level switching the pad.

3 GOhm resistor? Capacitors? Any component except bigger caps is under a thick coating.
PCB, capsule connector and bigger capacitors looks very different than the drawings in the service manual. Definetely a newer revision.
Capsule receptacle is soldered directly on the pcb (no stand-offs, no flexibility). Capacitors are on small plastic bases and looks similar to those used on motherboards....

I will try to swap the pcb between the two microphones too. Any other tip in troubleshooting?

Note: microphones have been used in studio and classical theatres, never in opened air and never been dropped.... bad batch from Beyrdynamic?

 

[Pule]

I had the same problem. One microphone had moisture problems. After drying, the situation changed significantly.

 

[Tim Campbell]

Well if it works when it's wet with alcohol and not when it's dry I would suspect a poor connection. Try resoldering the connections especially at the xlr since that is the place getting mechanical stress.

 

[Whoops]

Well if it works when it's wet with alcohol and not when it's dry I would suspect a poor connection. Try resoldering the connections especially at the xlr since that is the place getting mechanical stress.

I would suggest exactly the same just resolder and connections and solder joints, seems like a bad joint

 

[Tim Campbell]

Did you try this?

 

[Jim50hertz]

Hey @Lowfreq did you ever get this issue resolved? I have literally the same issue with my pair.

 

[Whoops]

Hey @Lowfreq did you ever get this issue resolved? I have literally the same issue with my pair.

Post photos of the PCB and also post the schematic

 

[OneRoomStudio]

Post photos of the PCB and also post the schematic

This is a current product of Beyerdynamic, so I don’t think posting a schematic is a viable option.

 

[Whoops]

This is a current product of Beyerdynamic, so I don’t think posting a schematic is a viable option.

Yes it is,
no problems whatsoever with that. You are repairing your own microphone which you have the right to do. You can post the schematic and you should in case you want help.

Problems with current products has to do with people trying to clone and starting clone threads for products that are still being sold.
But even that is in muddy waters, since people have been cloning here Neve preamps and EQs, SSL Bus compressors, All Urei 1176 revisions, Tektronix LA-2A, Neumann 87, Neumann U67, etc etc etc , and all those units are currently still being sold commercially.
So it seems it is what it is, anyway that's not your case

 

[Lowfreq]

Hey @Lowfreq did you ever get this issue resolved? I have literally the same issue with my pair.

Whenever I've opened the mic up and then put it back together, it always seems to go back to normal and work like it should, but 15-20 mins later it will always make a few weird sounds and then the volume drop happens again. I've cleaned the contacts and that hasn't made much difference. I do need to check the solder joints, but it's kinda slipped down my priority list, as I'm currently converting an old garage into my new studio, and all my time seems to be spent there.

I'm still planning on diving more in-depth into it again, as it seems such a waste of a good mic. It's been my go to pair on drum overheads for ages.

 

[Jim50hertz]

Thanks for chiming in guys. To clarify, I've been into the mic and resoldered the XLR connection to the PCB thinking that was the issue. As @Lowfreq says though, within a short space of time it's back to where it was...

 

[RuudNL]

This one?

 

[LevinGuitar]

I have the MC950 and it's a very useful mic! Was curious about what it have inside, thank you! (Hope this would not make me "mod" it in order to reduce caps xD :/ )

Offtopic but another example of a top mic that use two caps in paralell in audio path.

Aren't the rf caps values too big?

Also I'm curious about the unique capsule protection system they use in this mics. Some solid material that allows audio to pass through

 

[dom]

Did either of you ever figure out this noise issue with your MC930s? I have a 930 that I'm pretty sure is noisier than what I recall it being in the past. Unfortunately I purchased it used and a while ago, so no option for a warranty repair I believe.

 

[Jim50hertz]

I’ve sourced a repair tech in the uk who has dealt with this. Will be sending them off soon to get fixed, can report back afterwards.