Output MOSFETs getting hot.

[Perry Babin]

They can survive as long as they're cool. I know it's a pain to reassemble the amp to do initial testing. You can make a temporary heatsink out of 3/8" x 1" aluminum stock covered in kapton tape. The following example shows it keeping a regulator cool. You'd do the same for the full length of transistors. You may need to apply a thin layer of heatsink compound to the aluminum and the transistors to make it conduct heat efficiently.

 

[Ashleyzn]

Hi Perry I'm back to the same problem, it's becoming frustrating, replaced everything on the card except the 8 pin ICs just like i did in the weekend,replaced fets but not brand new but they test fine with a multimeter and I did the light test (saw a video of the light test on YouTube) all the fets looked good. Outputs are getting hot and the amplifier is drawing high current. Achim has the same problem.

 

[Ashleyzn]

I have read all your comments on doing the battery test and checking the signals on the gates but no conclusion to solving the problem.

 

[Ashleyzn]

Without the output fets and the driver card, the amplifier draws 2.5amps. install the driver card and the outputs the amplifier draws high current. I'm really losing hope now.

 

[Perry Babin]

I don't know what a light test is.

Battery test?

Are you using low voltage or full rail?

Where did you buy the FETs from?

 

[Ashleyzn]

Sorry not battery test. You do mention to connect a 9volt battery to rail voltage for the high side signal.

 

[Perry Babin]

That's used to supply the high side with voltage when the outputs are not in the circuit.

Are you using low voltage or full rail?

Where did you buy the FETs from?

 

[Ashleyzn]

To test MOSFETs using a light. Connect the ground of the power supply to the source and a light in series of the positive supply to the drain and use you finger resistance and touch the gate to turn on and off the light.

 

[Ashleyzn]

I'm using full rail.

 

[Ashleyzn]

I don't really understand were do you hook up your 9 volt battery.

 

[Perry Babin]

Where did you buy the FETs from?

 

[Ashleyzn]

Bought the fets from mantech electronics

 

[Perry Babin]

The 9v battery goes across the high side supply pins, 11 and 13.

Do you have low side pulses from the ICs?

 

[Ashleyzn]

I'm running out of options I spent a fortune on components and still no luck.

 

[Perry Babin]

These amps can be frustrating. Counterfeit components, components that are easily damaged when soldered in, the fact that the entire output section can fail catastrophically with a small problem all make them more risky to take in for repair.

 

[Ashleyzn]

You have To disconnect the rectifiers and remove the fets connect 9volt battery to pins 11 and 13 to check the high and low signals to the gates of the fets, should it be 10 volts peak to peak. The other question is do you still power up the main board.

 

[Ashleyzn]

The signal checks are to confirm if your drivers are good or bad am I right. If the drivers check out to be good then the only other thing that's a problem is that the MOSFETS itself,

 

[Ashleyzn]

Do you have pics on doing the signal checks and connections of the scope together with the battery connected and what the signals look like when it's good to be sure I'm doing the right thing. Am I asking for too much.

 

[Perry Babin]

#56:
How can you get power to the drive board without powering up the amp?

#57:
Yes. The test without the output is is generally good but I prefer going to low voltage rails with the outputs in the circuit. Its safer for all components.

 

[Ashleyzn]

What voltage should I apply.