Help/Troubleshooting - MXL CR24P (603 black chrome edition) - Not Working

[grtfldead1965]

Hi. I am new to this forum and hoping maybe I can get some input on an issue I am experiencing. I have two MXL CR24p (black chrome edition pencil style 603/991) mics that I have recently modded (replaced C3 & C4 with Panasonic ECQ-V .22uf metal film & C13 with Xicon Styroflex .001uf). One mic works fine after these mods, the other mic doesn't work (no sound). Here's what I am noticing...not sure if it helps or explains what is going on...but I measured voltage with my multimeter directly on the XLR cable with Phantom power turned on from my mixer (no mic plugged in yet) and I'm getting 49.5v at the XLR pins (measured across pins 1/2 & pins 1/3). So far, so good. When I connect the working mic to the XLR cable and measure voltage from pins 1&2 / 1&3, measuring at their respective connections on the circuit board where the wires are soldered, I am reading 35.7 volts. On the mic that isn't working, I am reading 4.2v at that same location on the circuit board. So I am trying to narrow down the cause of this issue but not sure where to start. I disassembled the XLR female end of the cable and pulled a reading directly off the XLR wires with the mic still plugged in and it is also reading 4.2v there as well. So something is causing the voltage to drop or the mic is drawing too much from the source and my assumption is that is what is causing the mic to not work because it's too low of a voltage . Does anyone here have any ideas on what may cause this sort of issue? Being somewhat a newbie at electronics, but not willing yet to just ditch the effort with fixing this mic, my thinking is to remove the new caps that I installed and re-install the original caps and see if it works then to at least rule out that the parts I installed are still good.. So I am more curious to see if this sort of issue that I am describing pinpoints to a specific issue/cause that you guys might know more about that I do. Any advice or suggestions to what I can do to solve this issue would be greatly appreciated.

 

[Khron]

Can you attach a photo of the non-working mic's circuit board? Especially on the side that you did the soldering on?

 

[grtfldead1965]

Here are pics.

 

[grtfldead1965]

Any ideas, anyone? If not, it's all good. Just a cheap mic that i was hoping to be able to troubleshoot and maybe learn something from. I'll keep messing with it and see what I can figure out. Again, was just looking to see if my description about the issue amd low voltage would point to any specific issues. Peace!

 

[Gus]

Did you measure the 4.2VDC with the PCB in the body? if so measure it again out of the body it is possible a part(s) is touching the body and there is a path to ground.
You also need to be carefull with the body screws with some SD microphones.

You would need to post voltages at different points in the circuit.
Voltages at the emitters, bases and collector of the PNPs

 

[grtfldead1965]

Hey there Gus! Yes, I did measure it with the pcb removed.

I will check the votages at the various locations you mentioned and get back to you. Thanks for the advice!

 

[Ike Zimbel]

I would check for shorts to ground and also check the new caps you put in for shorts, especially the Sufflex polystyrene cap. They are really touchy about overheating and can fail short if they get too much heat when soldering.