JRE Productions

Sennhieser MD421 help needed. (schematics or mechanical?)
« on: December 23, 2006, 01:37:04 AM »
I just got a vintage 421 U5 and it worked fine....until I opend it up.

I had removed the head where the capsule is located to fix up a few dents. When I did I broke a wire down in the base (not near the capsule). So I removed the area down by the switch and re-attached the wire. It did not work, so I removed the switch area and saw that I had a loose wire inside there. So I opened up the switch area where the transformer and (I am guessing) the pad circuits are located. (is that what the switch does?). I fixed all the loose wires and put it back together. Still did not work. I removed the XLR and there was yet another loose wire, I fixed that and still know workie! At least now, I can touch a wire while connected to an amp and here myself tap at all the wire locations including up at the capsule, but still no sound. (touching the wire so I can here the amp buzz). I had not tried the switch when I got the mic, but now the switch clicks 4 or 5 times but then spins past the last click if your not careful. Every thing I do to this thing seems to be a chain reaction to the next area.

Does anyone have schematics or a mechincal drawings of the switch area? Is there replacement parts available for this mic? Is there a service center anywhere? I just bought it, and would like the darn thing to work....

Note to self...you don't know sh*t about the inside of a mic.


JRE Productions

Sennhieser MD421 help needed. (schematics or mechanical?)
« Reply #2 on: December 23, 2006, 11:12:03 PM »
Thanks that actually did help a little even though it was written in German or Dutch or something.

I completely dissasembled the the mic and wiring. I replaced all the wires in the switch area and left a little extra in length. As you pull the mic apart, the wires were so short, you would break them off. While I was at it, I ran the ground wire as a home-run to the element ground. It grounds the entire case at that point. Before, the wire stop at 3 places along the way, but never touched the ground plane. It was just interim stops along the way to make it easier to assemble, which it did not. With the little extra length wire, I was able to pull the mic apart and get to all three sections. The xlr wiring, the switch wiring and the capsule wiring.

Here is where part of it was wierd and not working: The blue wire goes up to the capsule but not in it. It goes to a small coil of wire at the tip of the mic. From there the coil of the wire ends up going into the capsule and out the red wire. So there is a small coil or winding at the very tip. The small strand that attaches the blue wire to the coil never appeared to be soldered on to the blue post, just wrapped. The minute I added a small dab of solder to that connection, the mic started working. It must have worked fine for all these years before I opened it for the first time, so I am not sure how it made its initial connection.

ONE MORE SMALL QUESTION: Anyone have a solution to keep the capsule and head attached to the body? The capsule and head/grill just seems to push into the body. There appears to be no real way to fasten it in.

Thanks for the link!

Sennhieser MD421 help needed. (schematics or mechanical?)
« Reply #3 on: December 24, 2006, 12:00:45 AM »
IIRC the capsule mount pushes the grill into the body and the grill had screws to secure it to the mount.  (brain cells are a dying commodity here)


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