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Old 4th September 2010, 01:28 PM   #1
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Default Quested subwoofer noise...

Hi,

I have a Quested VS1115 subwoofer. Once I have wanted to check what the voltage it use for the opamp, but when I touched with DMM lead one of the pin of NE5532 opamp the two fuses blow up. They are in the point where the +-15V have to be. My fault. I thought I will replace them and everything will work on. But not. I have changed the fuses and in the subwoofer I hear noise such like a hum, but dirtier, something like DC noise.. I have changed the opamps, the same.. So I solder out carefully all Mosfets, there are 6 x IRF530 and 6 x IRF9530.. And tried to test with multimeter, with this method:

"1) Use DVM in diode test position
2) Holding red lead on S
3) Put put black lead on D. Reading should be between 500 and 800, you are measuring the forward voltage drop in the body diode.
4) Put black lead on G. Reading should be 1... (open circuit)
5) Hold black lead on S
6) Put red lead on D. You shuld read 1... (open circuit) as the gate should be retaining negative charge from step 4.
7) Put red lead on G, you should read 1... (open circuit)
8) Put red lead backon D, you should read a low value (close to zero initially, possibly rising very slowly). You are now measuring the D-S voltage drop with the gate positively charged in step 7."

The IRF530 everything shows up correct, just in the eight point it gives ~1.2V. It is low value? And all the IRF530 gives same result.

Same did with IRF9530, just with exchange + and - DMM wires.
Gave me the same result, just in eight point ~0.8/0.9V.

Can anybody confirm are the mosfets good?

Maybe anybody have some ideas what to measure and what else can cause such a noise in the subwoofer?


Thanks for any tips!
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