Sennheiser MD431 electronics repair?

[Christof]

The microphone does not output sound.

 

[rock soderstrom]

My hope therefore: The capsule should be fine - but something must be defective in the electronics (probably some of the Tantalum capacitors).

As member @RoadrunnerOZ said before, measure the capsule isolated from the circuit.

The tantals are always suspect but in this application they don't die as fast as in a PSU application. I would still check them all and see if they have continuity. Also test the magnetic switch to see if it still works. I would check the capsule first.

 

[Whoops]

The microphone does not output sound.

Ok,
so the first thing I would do is to test the capsule alone, not connected to the circuit.
If the capsule alone outputs sound, the problem is in the circuit.

If the capsule doesn't output any sound and measures Open, then it's game over,
no need to mess around with the circuit

 

[Christof]

To measure the capsule open I would rather not disconnect the wires directly at the capsule, but the wires on the circuit-board. But again - no access possible without removing the plastic shroud.

 

[RoadrunnerOZ]

I'm not one hundred percent sure, but it's the other way around. You can unscrew the switch completely, then the mic is always on AFAIK.

You may well be right there - best way is to meter the reed and see what it is at “idle”

 

[Whoops]

To measure the capsule open I would rather not disconnect the wires directly at the capsule, but the wires on the circuit-board. But again - no access possible without removing the plastic shroud.

If it’s possible that would be better for sure. The contacts at the capsule where the wires connect might be the same contacts where the thin coil wires are soldered also.
Sonic possible it’s better to remove the wires from the PCB.

Although I’m the past with other mics I unsoldered them at the capsule tabs when I had no other chance

 

[RoadrunnerOZ]

To measure the capsule open I would rather not disconnect the wires directly at the capsule, but the wires on the circuit-board. But again - no access possible without removing the plastic shroud.

Can you post some better photos of the plastic where it fits to the inner casing - that should give a clue as to how it comes apart

 

[Christof]

One earlier reply had to be checked by a moderator: Sennheiser MD431 electronics repair?

In that post I wrote: Having a closer look you can see on the photo that the plastic shroud is clipped on with some kind of "teeth". I tried to loosen those, but they are quite rigid.

I will post some better photos later.

 

[RoadrunnerOZ]

One earlier reply had to be checked by a moderator: Sennheiser MD431 electronics repair?

In that post I wrote: Having a closer look you can see on the photo that the plastic shroud is clipped on with some kind of "teeth". I tried to loosen those, but they are quite rigid.

I will post some better photos later.

From what I can make out it looks like it needs to rotate to clear rather than trying to lift the tabs - they may break - is there a recessed screw - it looks like it in No. 2 photo - in a lot of mics the screw goes in to free the outer casing. Sometimes you need to push in, rotate and then pull - you should be able to see through the acrylic if there’s a keyway for the teeth to follow to remove the casing. I use a head mounted magnifier with a Cree LED light to work on mics and fine SMD components.

 

[RoadrunnerOZ]

To measure the capsule open I would rather not disconnect the wires directly at the capsule, but the wires on the circuit-board. But again - no access possible without removing the plastic shroud.

Just hook a scope across the capsule terminals without disconnecting and see if audio is delivered with the mic sitting on a table and slap the table with a ruler or output a sine wave from a tuner app on your phone next to the mic - if you get a good signal the capsule is ok.