camarada78

Sennheiser vintage md-421 wiring and readings
« on: April 07, 2021, 03:17:40 PM »
hello,

I got two md421 as junk in an auction as they were cosmetically acceptable. One of them is really old (it was the white/beige one but someone spray-painted black... go figure) after reataching some wires i get around 9 ohms on the upper coil (blue and center pin on capsule) but get no reading out of the red wire.

Anyone experienced with these? What readings should i get?

have a good day

- i've attached a picture

Anything that is too stupid to be spoken is sung


Whoops

Re: Sennheiser vintage md-421 wiring and readings
« Reply #1 on: April 07, 2021, 06:47:58 PM »
You should get around a 200 to 230 ohm DC resistance reading with the multimeter

camarada78

Re: Sennheiser vintage md-421 wiring and readings
« Reply #2 on: April 08, 2021, 04:20:14 AM »
I got nothing. Diaphragm is dead and too thin to rewire. If only I could get a new diaphragm the capsule could be salvaged. Almost impossible to resolder.
Anything that is too stupid to be spoken is sung

Whoops

Re: Sennheiser vintage md-421 wiring and readings
« Reply #3 on: April 08, 2021, 07:02:17 PM »
Forgot to say but the 200-230 ohms reading is between Pin2 and Pin3 of the XLR

camarada78

Re: Sennheiser vintage md-421 wiring and readings
« Reply #4 on: April 08, 2021, 09:47:11 PM »
Forgot to say but the 200-230 ohms reading is between Pin2 and Pin3 of the XLR

I got no reading because that should be around the measurement straight from the diaphragm. Since it is broken it will read nothing. Sennheiser doesnt sell just the diaphragm with coil so i'm on a quest to find a replacement for just the diaphragm. It is a waste to through out a whole capsule with bobin and magnet just because they wont sell a U$10 dollar a piece diaphragm.
Anything that is too stupid to be spoken is sung

Whoops

Re: Sennheiser vintage md-421 wiring and readings
« Reply #5 on: April 08, 2021, 10:30:34 PM »
I got no reading because that should be around the measurement straight from the diaphragm. Since it is broken it will read nothing. Sennheiser doesnt sell just the diaphragm with coil so i'm on a quest to find a replacement for just the diaphragm. It is a waste to through out a whole capsule with bobin and magnet just because they wont sell a U$10 dollar a piece diaphragm.

You can get diaphragm donors from other mics although I don't think it's an easy operation to replace it.

It's unfortunate since there are too many 421 mics broken or with low end loss that could be repaired.

panman

Re: Sennheiser vintage md-421 wiring and readings
« Reply #6 on: April 09, 2021, 10:23:09 PM »
I got no reading because that should be around the measurement straight from the diaphragm. Since it is broken it will read nothing. Sennheiser doesnt sell just the diaphragm with coil so i'm on a quest to find a replacement for just the diaphragm. It is a waste to through out a whole capsule with bobin and magnet just because they wont sell a U$10 dollar a piece diaphragm.
You are mixing up "diaphragm" and "voice-coil". You can measure the resistance of the voice-coil and not the diaphragm. The capsule does not look like it would be worth saving, because it obviously has been swimming in dirty water. The ventings are blocked and they need to be clean in order the mic to work properly. Also the basket has been violently torn off and it is broken, so you need to replace that too. The diaphragm might be ok, but the coil is likely jammed and the magnet gap full of dirt. To fix that mic requires expert level of knowledge and skill(of repairing MD421) and there is not much chance of succeeding the first couple of times(I did many before succeeding to get the proper sound with full bass), but it is not forbidden to try. You don`t have much to loose with that one anyway and you might get really lucky. Use the search function here and you `ll find many usefull threads about MD421. 


 

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