Sennheiser MD421-U still possible to repair ?

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beatnik

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I am wondering if anyone here had experience repairing these older MD421-U ?

Seems the replacement capsules are not available anymore as now the current production model is MD421-II and Sennheiser europe told me the newer capsules do not fit MD421-U models

Do you know anything about fixing these mics or where to find nos capsules for older model?

Thanks


 

ln76d

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What's wrong with the old capsule?
I repaired a little bit of them. In some just need to glue the diaphragm (weak bass response), some need soldering broken winding (no output) and some need to change the diaphragm/coil.
Those capsules are really easy to work with it (better than AKG capsules), enamel from the wire is excellent to remove it with soldering iron and all the types of repair i mentioned are possible :)
If you will write something more about the damage i can help you.
 

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beatnik

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that is good info

i don't have them at the moment but i will get back soon and report what i find once opened them

thank you
 

shot

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While Beatnik is waiting for his mic, I'll hijack the thread with the problem I have with one of my MD421!

It has constant buzz/hiss and a bit lower level than other mics of the same type I own. I thought it was a broken wire so I opened it but all the wires seem to be ok.
Is there a place where ground connection might have fallen off?
What would be the way address this issue?

best,

Luka
 

ln76d

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shot said:
It has constant buzz/hiss and a bit lower level than other mics of the same type I own. I thought it was a broken wire so I opened it but all the wires seem to be ok.
Is there a place where ground connection might have fallen off?
What would be the way address this issue?

What is the suffix of that 421? Maybe HL or HN? XLR? Klein Tuchel? Groß Tuchel?
I'm assuming that the frequency response is ok, so "buzz/hiss and a bit lower level" looks like wiring issue, it could be ground disconnected or overall bad wiring.
Check with multimeter (diode checker) if the pin 1 of XLR (pin 2 on Tuchel - except HL/HN version) has connection to the other pins and connector metal housing.
You can remove/desolder the connector/switch module (newer versions have pin connectors so you don't need to desolder them) and try to solder wires to any XLR male inlay from the plug. Standard colour scheme of symmetrical connection. Connect it careful (don't pull the wires) to the microphone cable and check. If it help, we will look for the switch issue, if not - the capsule wiring :)
 

ln76d

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jordan s said:
I've got a few with low bass response. Any tips would be super helpful.

Do you hear any difference in bass response using "m-s" switch?
First you can try direct connection which i described for Luka.
To remove connector module you will need to remove name plate, underneath which is the screw.

I wrote the whole disassembly/repair instruction, but my laptop battery discharged and i lost it ;D
If this will not work i will write once again whole instruction :)


 

DerEber

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I glued a diaphragm crack in an 421 with low bass response.
It was only a very  small crack so lock out with an magnification glass.
Helped for good.
2 month later the  compensation coil felt off.
:D

At least it still looks good....
 

ln76d

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What a pity :D
I glued coils too, it's awful work :D
If you can take off glued diaphragm without problems, you can always change it.
From what i remember best replacement is md408 (which goes cheap) or use md405/ grundig gdsm 202 (thinner diaphragm foil) - a minor audible difference. There's a many sennheiser mikes which share same size of diaphragm and identical coil. Unfortunately most of it is overpriced today.
From the late 80's/early 90's there are md908/md918. They will fit too, but the coil lamination is worse to remove (if you will need of course).
908/918 are cheap mikes but excelent sounding :)
 

Knuddi

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ln76d said:
What's wrong with the old capsule?
I repaired a little bit of them. In some just need to glue the diaphragm (weak bass response), some need soldering broken winding (no output) and some need to change the diaphragm/coil.
Those capsules are really easy to work with it (better than AKG capsules), enamel from the wire is excellent to remove it with soldering iron and all the types of repair i mentioned are possible :)
If you will write something more about the damage i can help you.

Long shot I know - this is an old thread, but here it goes:
I've got a defective MD521 Blackfire which is almost identical to the MD421.
I have located the failure to be a broken coil (not the humbucking coil on top) and my problem is how to get the capsule disassembled without completely destroying the unit. I hope that mayby the enamel wire have been disconnected from one of the terminals, but  I'm uncertain how to get the upper plasticpart, holding the diaphragm, off. Should I just "pull it off" with severe force, by means of a screwdriver inserted between the upper and the lower plastic part?

Regards, Knud
 

panman

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Knuddi said:
Should I just "pull it off" with severe force, by means of a screwdriver inserted between the upper and the lower plastic part?

Yes, you need to pull it off, but very gently. The plastic snaps easily plus the diaphragm may get damaged.  Once you have it off, you just follow what was written on this thread before.  Having done a lot of repairs for these and  other Sennheiser capsules, I would not call it "easy repair" though.  Yes, a lot of things can be done by an expert, but nobody becomes that without learning by doing.
You may  get lucky the first time , but most likely not.  Well, at least I didn`t, but my failures taught me the most.
 

Knuddi

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panman said:
Yes, you need to pull it off, but very gently. The plastic snaps easily plus the diaphragm may get damaged.  Once you have it off, you just follow what was written on this thread before.  Having done a lot of repairs for these and  other Sennheiser capsules, I would not call it "easy repair" though.  Yes, a lot of things can be done by an expert, but nobody becomes that without learning by doing.
You may  get lucky the first time , but most likely not.  Well, at least I didn`t, but my failures taught me the most.

Thanks for the reply.
Shall I be able to put a screwdriver here where the arrow points and wrickle the plasticparts apart?

MD521Capsule.jpg.html

MD521_Closeup_of_diaphragm.jpg.html

MD521_Closeup_of_diaphragm_w_arrow2.jpg.html
 

Knuddi

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panman said:
Yes, that`s the place.

Thanks a lot - I'll give it a try tonight.
Hopefully I'll be able to do it without destroying something.
But it appears to be extremely firmly glued to the other plastpart - right?
 

Knuddi

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I have gotten so far as to have removed the humbucking coil, but I still need to get "under the hood" to see if I can repair the voicecoil.
Anyone who have managed to get the membrane off?




 

Whoops

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Interesting thread,
I never took a diaphragm of one of these capsules, but theres a lot of these microphones worldwide that need to be fixed so it would be great to find a method for it.

I have some 421 documents that might help in your repair, send me a pm with your email and I send you what I have

Wish someone can chime in and bring some help and insights
 

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