repairing my AT2021

[jtn191]

What happened? Left my interface on overnight and eventually my AT2021 only outputs LOUD white noise. What could have gone wrong? a bad cap? bad transistor? btw transformer is labelled "0915" on top, must be a part number, EX140316 on side, x2 "C106" caps, 1004 resistor, 5602 resistor, "2L" transistor, 1001 resistor, "3" diode, 47 uF 50 V electrolytic front and center.

pic https://imgur.com/a/o7tkApn

 

[radardoug]

This is like saying, 'My car wont start, why?' We dunno! Did you put gas in it?

 

[jtn191]

I know...I opened it up to see if anything looked suspect. Just wondered what would be anyone's first guess for a component to fail. If I had to guess, I'd think the 47 uF might be the likeliest culprit, but I was asking for a second opinion

 

[Khron]

"0915" is rather more likely a manufacture date code, ie. 15th week of 2009.

Do you have any other mics you could use to rule out the interface as the source of the noise? And/or something else you could plug the AT2021 into?

 

[Gus]

First thing to do is try another microphone with the audio interface or another audio interface with this microphone like Khron posted.

There might be parts under the foam
2L SMD looks to be a MMBT5401
https://www.el-component.com/bipolar-transistors/mmbt5401

Are there parts on the other side?

Do you know how to use a DMM to measure voltages?

If there are parts on the other side of the PCB or under the foam compare the circuit to  the  JFET to PNP  microphone circuits you can find on the web

 

[jtn191]

"0915" is rather more likely a manufacture date code, ie. 15th week of 2009.

Do you have any other mics you could use to rule out the interface as the source of the noise? And/or something else you could plug the AT2021 into?

yes, all my other mics and DI'd instruments work.

First thing to do is try another microphone with the audio interface or another audio interface with this microphone like Khron posted.

There might be parts under the foam
2L SMD looks to be a MMBT5401
https://www.el-component.com/bipolar-transistors/mmbt5401

Are there parts on the other side?

Do you know how to use a DMM to measure voltages?

If there are parts on the other side of the PCB or under the foam compare the circuit to  the  JFET to PNP  microphone circuits you can find on the web

Yeah I use a DMM and work full-time in electronics. I can try applying phantom power, but I'm not sure what I should be looking for without the schematic. I could try reversing the schem out of curiosity. Looks pretty simple

 

[Gus]

Measure and post the voltages at the pins of the transistor the zener etc compared to ground(pin1).

When I trouble shoot a phantom powered microphone I use a stand alone P48 supply I built.

If there is aJFET under the foam this might be something like the ST51 or MXL2001,v67 etc without the EQ
or the other
N channel JFET, PNP  circuits you will find on the web. If so this can make the tracing of the circuit faster.

With the microphone disconnected check both sides of the transformer to check if a winding is open.

Is there high humidity where you are?

 

[jtn191]

on it 

Is there high humidity where you are?

yes, where I used to live--and where it happened-- was VERY high humidity