A challenge for me

[yurijeik]

Hi,
My name is Yuri and I'm from Brazil, been trying to get my first mic to mod and found a used AKG P220 for just $50 on the used market but one challenge... It is defective, I really want to try to fix it and would appreciate any directions on how to diagnose the problem, and what is happening... The mic is way quieter and with a constant "wind" noise even tho the quality of the recordings are great, I've noticed drop marks but on disassembly the circuit and capsule looks all intact, I have experience fixing electronics so if anyone wants to help me on this adventure just ask me for anything. Also it's connected to my Native Instruments Komplete Audio 1 Interface (with the +48V switch on) and the -20db switch on the mic is at 0 position.

 

[Khron]

Internal photos (of the circuitry, mainly)?

A Perception 200 i got as faulty years ago ended up having one leg of one of the 1Gohm resistors broken off, which rendered the whole thing mute (or just noisy, can't recall exactly). Replacing that revived it instantly.

 

[yurijeik]

Internal photos (of the circuitry, mainly)?

A Perception 200 i got as faulty years ago ended up having one leg of one of the 1Gohm resistors broken off, which rendered the whole thing mute (or just noisy, can't recall exactly). Replacing that revived it instantly.

I'll send detailed photos today

 

[yurijeik]

Got some pics here, I've noticed that both green "resistors" with two red bands at the pcb C got cracked and I can feel it with my nail.

 

[yurijeik]

New thing discovered!
The mic works! It was very quiet and had a wind like noise but I just let it connected and it got back to normal, but when I say ploxives too close to it than it goes back to quietness and wind humming noise for some seconds. Do you thing maybe the capsule has something wrong? I've heard before about membrane sticking.

 

[Khron]

both green "resistors" with two red bands at the pcb C

Which one's "PCB C"?

when I say ploxives too close to it than it goes back to quietness and wind humming noise for some seconds

Might be worth sticking it into a sealed bag with a few sachets of fresh / baked silicagel, to dry out whatever moisture may be there.

 

[yurijeik]

Which one's "PCB C"?



Might be worth sticking it into a sealed bag with a few sachets of fresh / baked silicagel, to dry out whatever moisture may be there.

The one with the two green big resistors and a bunch of SMD caps and diodes, it has a C on the silkscreen, the rectangular one that is not soldered to the XLR and doesn't have the transformer.

 

[Khron]

... And that's in none of the photos (as far as i can see)..?

 

[yurijeik]

... And that's in none of the photos (as far as i can see)..?

This, sorry!

 

[yurijeik]

I measure 5 ohms on both with my multimeter.

 

[Khron]

Ouch, those indeed don't look good at all. Those may or may not affect tge issue you're facing, but they definitely don't help.

Those are two inductors, and i *think* they're 220uH each. You can check the capsule bias voltage between ground and the yellow-circled point (with the mic electronics assembled and phantom power on, of course):

 

[yurijeik]

Ouch, those indeed don't look good at all. Those may or may not affect tge issue you're facing, but they definitely don't help.

Those are two inductors, and i *think* they're 220uH each. You can check the capsule bias voltage between ground and the yellow-circled point (with the mic electronics assembled and phantom power on, of course):

Oh inductors... I'll try to buy them here in Brazil, also which voltage readings should I expect to measure?

 

[Khron]

At that node, about 60V DC, if all is well.

 

[yurijeik]

At that node, about 60V DC, if all is well.

Okay, measured 45.5V soo there is something wrong after all

 

[bremusound]

Well it depends on your voltmeter. An ordinary voltmeter will show you less voltage than generated. You would need an electrometer or a voltmeter with an extremely high input impedance.

 

[yurijeik]

Well it depends on your voltmeter. An ordinary voltmeter will show you less voltage than generated. You would need an electrometer or a voltmeter with an extremely high input impedance.

I used a Yokogawa TY720, is there a chance that the cracked inductors are lowering the bias voltage?

 

[Khron]

Well it depends on your voltmeter. An ordinary voltmeter will show you less voltage than generated. You would need an electrometer or a voltmeter with an extremely high input impedance.

Not necessarily - i indicated that node precisely because it's BEFORE a series 1Mohm resistor (the one just to the right, before that trace that goes right and curves upwards towards the first pin of that 5-pin connector).

45V is a bit lower than usual, but that should only result in maybe 1dB lower output than "normal".

Those cracked inductors may or may not be the cause of the noise, but you'd want to replace those sooner rather than later, anyway. So you can start with that, but don't necessarily expect that to solve the noise / pop sensitivity issue.

Might be worth sticking it into a sealed bag with a few sachets of fresh / baked silicagel, to dry out whatever moisture may be there.

 

[yurijeik]

Not necessarily - i indicated that node precisely because it's BEFORE a series 1Mohm resistor (the one just to the right, before that trace that goes right and curves upwards towards the first pin of that 5-pin connector).

45V is a bit lower than usual, but that should only result in maybe 1dB lower output than "normal".

Those cracked inductors may or may not be the cause of the noise, but you'd want to replace those sooner rather than later, anyway. So you can start with that, but don't necessarily expect that to solve the noise / pop sensitivity issue.

Thanks for the help, one more question... I've searched for 220uH inductors and found only with 4 colored bands and the ones inside the mic have only two red bands... Are they really 220uH inductors? Just to be sure, and the silica gel filled bag strat is going for all night, I'll share the results about the ploxives cutoffs.

 

[Khron]

Are they really 220uH inductors?

I'll double-check when i get home after work, but i'm pretty sure they are.

http://cdn.recordinghacks.com/images//mic_extras/akg/perception220-pcb.jpghttps://audioimprov.com/AudioImprov/Mics/Entries/2013/2/26_AKG_Perception_220_files/P1010335.jpg

 

[yurijeik]

I'll double-check when i get home after work, but i'm pretty sure they are.

http://cdn.recordinghacks.com/images//mic_extras/akg/perception220-pcb.jpghttps://audioimprov.com/AudioImprov/Mics/Entries/2013/2/26_AKG_Perception_220_files/P1010335.jpg

Huh, weird that these look soo different than the ones on my mic, they're even soldered one flipped compared to the other while mine have the red bands to the same side