As far as I know Sennheiser still does repairs with a valid RMA. What you call them to get the RMA, find out if they will refurb to the old original 421 or will it become a fixed 421-MKII? They may no longer be able to repair with the older original 421 parts. Please let us know the outcome for future reference.

If the main or only problem is that it sounds thin, then maybe you can get away by fixing the HPF-setting. There's a tiny piece of plastic inside thats both easily broken _and_ sets the 5-position hi-pass. If it's broken, the ring around the connector can turn without end-stops and the actual setting can be anything - probably the one with the most bass-attenuation.

Unlikely that this is your whole problem, but you never know.

Bye,

Peter

Peter: Thanks for your comment, and it may actually be close to the truth. The "ring" on the U3 is broken in that it does not "click" when you rotate it from the M to the S position. the previous owner told me that the detents on the ring were broken, but that the filter still worked. I wonder now...

When I asked him about the sound, he acted surprised, and said that he really didn't use it much (which is why he sold it) after buying it a few months ago on Ebay. He said he tested it on guitar cabs and some vocals, and it sounded fine.

It did not sound good at all to my ears! (In fact, it was one of the most horrible sounding things I have ever heard!!!! ;) ).

So I wonder how to check on this inside ring...does it easily come apart? Once I open it, I can probably figure it out. I usually use my other 421 on the M position anyway, and rarely rotate it anywhere else...

Thanks for that advice, it is certainly worth checking out.

My 421 that had that problem is the old grey one, with the 3-pin DIN plug, it's the MD 421 N if I'm correct. It didn't sound horrible, but thin it was.

On models with the HPF there should be five detents and five the number shall be. If otherwise or no endstops at all I don't see how it could still be functional w.r.t. filtering-control. And definitely not how you can know which position the filter is in.

On the mic I have you see a metal ring between the actual connector and the plastic ring. There are two holes in that metal ring. Loosen this ring, by hand of this can't be done use something that gives you more grip by using those two holes.

Sennheiser probably has a specialist tool for this, but using pliers with sharp points can work as well.

Loosen the ring, remove the plastic ring and be sure to catch the little metal ball that should jump out. You'll also find a (probably broken) small piece of plastic, controlling the internal 5-position switch and kept in place by a cavity in the plastic ring. I made myself a new tiny plastic thingy from PCB-material but that didn't last long (once other bandmembers get hold of the mic...)

Make one from metal - or contact Sennheiser, perhaps they provide these parts for a decent amount. I solved it by using the piece of plastic of a broken other 421.

BTW, the MD 441 has the same construction w.r.t. the HPF.

Bye,

Peter

Great Post Peter! I had one of the grey 421's at one time and this was the problem with it too..the HPF adjustment ring and come loose from the actual adjustment on the inside and nothing was happening.It sounded thin and was useless.The repair was cheap and now I would do it myself but then I was but a plebe....

I just removed the hi pass parts all together on one I had problems with. Now it sounds better than our other one with the working hpf.
cheers

Nice, good to hear this could have been the problem, as it's easily fixed. Let us know if someone has tried to get a replacement from Sennheiser for the little broken part. If it's worth while or not for an inflated price I'll get me a few.

I just removed the hi pass parts all together on one I had problems with. Now it sounds better than our other one with the working hpf.

Hey cool !
Nice suggestion, since I can't remember having used other switch-settings than the 'M'-position.

Makes me think of removing all pots & caps in an electric guitar and get a better sound.

Bye,

Peter

Peter

The metal ring you're talking about is called a 'segir ring' if memory serves me well.

It't the same ring that is found in pistons of car engines.

Every car toolshop has the small tool that will make the removing of the ring a piece of cake. :D

'segir ring'

Ah, never heard of before. Always good to know. But manufacturers should stop using specialist stuff like this ! :-)