Precision power A300 blown power supply

[chipper]

Hey guys got a blown precision power amp here I need help checking if the driver circuitry is working or identifying it on the main board. As far as I can see power supply is blown. I believe the original power supply fets are IRFZ44? Any help greatly appreciated. Thanks!

 

[Perry Babin]

From the photo, it appears that the 3525 drives the FETs without any driver transistors.

 

[chipper]

Originals were IRFZ44 can I use IRF3205? Also at what voltage is it suppose to be on the gate pads?

 

[Perry Babin]

The 3205s should be OK with 47 ohm gate resistors.

Most meters will read approximately 5v on the gate pads. This will vary greatly by meter and if the supply is regulated (when the FETs are in the circuit).

 

[chipper]

I have 7.5 volt on all four gate pads.

 

[Perry Babin]

That's very high. If the amp had driver transistors, it would appear that the PNP drivers were defective. Side note, the DC voltage is typically a little less than 1/2 of the 12v supply voltage. If you have 16v feeding the amp, the 7.5v may be OK.

Do you have a scope?

 

[chipper]

Yeah I figured. There is two MPSA56 transistors near 3525AN chip. I don't have a scope just a meter.

 

[Perry Babin]

Confirm but I think that the two output pins of the 3525 go directly to the gate resistors (0 ohms).