kostix

AKG P220 microphone failure repair.
« on: October 16, 2017, 05:10:25 PM »
Hello to all!

Recently I have been given for repair an AKG P220 microphone and it has a peculiar failure, my client told me that it didnt not work.. i ran some tests, apparently it works but if I say something very loudly right into the capsule screen, the output sound goes totally off and then very slowly recovers back, sometimes with what sounds like a very random low-passed noise. I am wondering if the capsule is damaged somehow and goes out of spec of the rest of the circuit after receiving a stronger acoustic shock (a loud shout right into the mic) or the failure is part of the circuits.
I have an AKG P420 mic at hand and it does not behave like this, the output never goes dead no matter the level of sound close to the screen.
I tested the P220 with a cheap Phonic console I have here (which measures around 51V on the phantom lines unconneted to the mic) and it behaved like this when strong levels of sound are produced right at the capsule. I left it laying on a table without touching it recording  the room ambience for 4 hours and it did not fail once.
After testing I gave it back to my client who tested it with a Tascam computer interface, as well as with using an external phantom power supply and he reported back that the sound goes out/off periodicaly, kinda randomly and back on, so no stable correct operation.

The P220 mic is the black model with entirely surface mount components on the boards. The mic is out of warranty so mostly its up to me to figure out how to repair it.

I have a Neumann mic at hand and I was thinking of swapping the capsule with the AKG to see if that will indicate if the problem resides in the capsule or the circuit, but still have to try it.

Any advice would be greatly appreciated.

Best regards,
Konstantin


Khron

Re: AKG P220 microphone failure repair.
« Reply #1 on: October 16, 2017, 05:16:24 PM »
Kinda sounds like the diaphragm sticks to the backplate, when too much airflow hits it. How dirty is it?

It might be interesting to stick the mic (or at least the capsule) in a sealed bag with as much silica gel (ie. desiccant) as you can get.
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ln76d

Re: AKG P220 microphone failure repair.
« Reply #2 on: October 17, 2017, 11:24:02 AM »
Didn't stick to the backplate, it's just dirty - i cleaned many perceptions capsules. 200,220,400, 420.
It's also typical for NT1a with k67. Both mikes works with high polarisation voltage (in nt1a it's just insane!!!) and the dirt glued by saliva is enough. Design of the circuit partially sucks, can be improved ;)

kostix

Re: AKG P220 microphone failure repair.
« Reply #3 on: October 17, 2017, 08:51:59 PM »
Hey guys, thanks for the point outs. From your personal experience, what is an appropriate, doable procedure for cleaning such a surface? The capsule is indeed kinda dirty from what I recall.

Best regards,
Konstantin

ln76d

Re: AKG P220 microphone failure repair.
« Reply #4 on: October 18, 2017, 05:37:41 AM »
Distilled water and delicate brush - don't even try for the first time on your customer capsules ;) Find some cheap capsule and learn first.