Rockford T600-2

[imraneesa]

Got this amp with blown power supply fets and driver transistors. Fets were IRFP064N. This amp was repaired earlier and technician had spoiled someone the vias of power supply driver board. I changed fets to 75344g and also gate resistors 51.1ohms. Amp coming on and producing good clean outputs. But power fets gets very hot at idle. And almost pulling 2.1amps. Any suggestions?

 

[Perry Babin]

What's the idle current before the output stage is enabled?

Are the gate signals all clean and driving to ground?

 

[imraneesa]

Idle current is about 2amps without anything connected. I don't see any time gap between enabling outputs. As I power up it will spike little bit and stays at 2amps.
Gate signals looking good.

 

[Perry Babin]

What's the board number on your PS driver board?

 

[imraneesa]

Picture showing number of driver board and waveform attached.

 

[Perry Babin]

The drive looks OK. It may be a bit lower with lower value gate resistors but that can wait.

If you reduce the bias current (full CCW on bias pots), do the PS FETs heat up?

 

[imraneesa]

I turned the bias full counterclock wise already. Still they heats up

 

[Perry Babin]

I would try reducing the gate resistors. I don't have this diagram but the T400 uses 34 ohm resistors. Rockford goes as low as 22.1 ohms with that PS FET.

I'd go down as little as possible for the FETs to run cool. Then drive the amp hard for at least 10 minutes to confirm that there is no heating of the primary filter caps.

 

[imraneesa]

What if I use IRFP064N?

 

[Perry Babin]

The FETs you have are OK and used in Rockford amps. Any time you make a change, you have to expect the unexpected.

What were the original gate resistors?

Why did you change to the 75344 if you have the 064?

 

[imraneesa]

I saw in some rockford they used 75344. As I said this amp came from technician. So I was guessing if he changed them. Amp came with 064 and 51.1 ohm gate resistors.

 

[Perry Babin]

Well... you'll have to change something if you want to reduce the current draw.

If you have 47 ohm resistors, try those. That may be enough.

 

[seankane]

Rockford used the 75344 from the factory. I've used 064 in many Rockford amps with success and never any issues.

 

[seankane]

I've always used 47 ohm gates with the 064's and never had any issues.