Sony C37P DC/DC Converter Problem.....

[la-2a]

Hello people, I'm in the process of bringing a Sony C37p back to life. I suspect the error (too little level) in the DC-DC converter. A question for the experts. Can anyone confirm the correctness of this circuit? Somehow I don't quite understand it. The conductor tracks don't quite correspond to the circuit diagram either. In addition, there are no names printed on 2 components that should actually be diodes. Unfortunately I can't measure anything even when it's removed. I marked it in the photo. I really appreciate your help and would be happy to be able to solve my problem.

 

[Khron]

Yes, it would make total sense for that to be another diode.

 

[la-2a]

Hello, I cannot measure the polarization voltage with my voltmeter. To make sure that the DC/DC converter or the CL 112B module in which the FET is located is defective, I would like to connect a Chinese tube power supply that supplies 135 V to see whether the CL 112B is OK. . Please help me get the 140V to the right place without breaking anything. I have attached the circuit diagram. Thank you very much.

 

[JohnRoberts]

I do not recognize that topology.

The component in question may not be a diode, that does not appear to provide any functional purpose. Perhaps a resistor there could serve to RC smooth the output. Alternately if the supply is using a cap as a doubler the circuit connections do not look correct.

Sorry not much help.

JR

 

[Khron]

I would like to connect a Chinese tube power supply that supplies 135 V to see whether the CL 112B is OK. . Please help me get the 140V to the right place without breaking anything.

Why would you want to apply 140V ANYWHERE inside that mic???

 

[la-2a]

The microphone requires a polarization voltage of 140V. To get the 48V Phantom to 140V you need the DC-DC converter. The module that houses the FET and some resistors is called CL 112B and is potted. Both tend to be broken. To make sure the CL 112B module is OK, I thought about testing the mic with the external polarisation PSU instead of the DC DC converter. NOT ANYWHERE . Since I'm not sure about the correct connection, Voltage + or - DC and don't want to damage the output transformer and module. I wanted some assistance.

 

[JohnRoberts]

If that's a typical charge pump/doubler circuit, the bottom of the middle capacitor may not be connected to ground but instead to the transformer. Just my WAG.

JR

 

[Khron]

If that DC-DC schematic is accurate, you'll want a negative voltage with respect to ground.

 

[la-2a]

That's a good question. I have the circuit diagram from the gyraf site. Somehow the circuit does not correspond 100% to the conductor tracks. @JohnRoberts which capacitor do you mean, the one betweed the 2 diodes. @Khron as I understand it, I leave the 48V connected to the XLR input and apply a -90V negative voltage to the pins of the DC DC converter.? You might have a look on my post #3 PDF with the complete schematics...

 

[Khron]

http://recordinghacks.com/images/mic_extras/cad/gxl3000-schematic.png

This contains a Schoeps-type oscillator, but with a voltage multiplier on the output. Likely what's supposed to be in the C37P, just with the diodes pointing the other way.