Power Acoustic, unhappy mosfets

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Scanlines

Member
Joined 2007
myspace.com/akgservice
Hi there;

I'm having trouble with a Power Acoustic A4200db

I've replaced all the fets in the power supply,
and their gate resistors.

I used RPF70N06's in place of the IRFZ46n's that were in there.

All the output fets are new as well.

It powers up fine, but draws too much current idling.

I see that the fets on one phase are happy, but the ones on the other phase of the power supply are getting pretty hot.

With a scope, and all the fets out of the circuit, the waveforms on the PMW chip are uniform, but when I insert
the new fets back in, one phase gets skewed


You can see by this picture, the top wave has quite a bump on it, that's the problem phase.


I was thinking maybe a shorted torroid, but this is a split PS with 2 transformers why would just that phase get go squirly on both ?

Got any ideas ?
 

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Perry Babin

Member
Joined 2003
bcae1.com
If the driver transistors are not defective, all of the gate and pulldown resistors are within tolerance and there are no open traces, the driver IC may well be defective.

Does the gate drive signal for any power supply FET (taken from the gate leg of the FET) look different than the gate drive signal on any other power supply FET?
 
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