Rockford Fosgate P300-1

[Jason Smith 616]

I replaced the Power supply fets,outputs, power supply drivers.

When trying to power the amp up the yellow protection light flashes ..

Anyone have any ideas?

 

[Jason Smith 616]

the amps protection light keeps flashing but the amp will power up and protect and it cycles like this constant.

Ive been trying to track the problem down but cant find anything

 

[seankane]

Were the power supply gate resistors within tolerance?


Did you check the gate resistors, drivers, and source resistors for the outputs?


If all this is good you may have a problem on the A/B driver card.

 

[seankane]

Generally they only do this when something has a direct short.

 

[Jason Smith 616]

The gate resistors were burnt and out of tolerance

The source resistors and drivers and gate resistors for the outputs check fine.

I replaced the drivers for the power supply.

Could the 494 be defective?

Im getting 12 volts at the power supply fets but im getting 17 volts on pins 8,11,12 of the 494

 

[seankane]

They rarely fail but its possible. Are the regulators outputting the proper voltage?

 

[Jason Smith 616]

Regulators are fine they output the correct voltage.

If i take the outputs out of the amp the light stops flashing but the power light never comes on.

Heres what i get on the 494

Pin 1:2.28
Pin 2:2.49
Pin 3:0.07
Pin 4:0.00
Pin 5:1.53
Pin 6:3.44
Pin 7:0.00
Pin 8:16.38
Pin 9:6.60
Pin 10:6.60
Pin 11:16.38
Pin 12:16.38
Pin 13:5.02
Pin 14:5.02
Pin 15:5.02
Pin 16:0.00

Wondering why the voltage is so high on pins 8,11,12

Do the rest of the voltages look correct or maybe i have a defective 494

 

[Perry Babin]

8, 11 and 12 are fed by the +15v regulator after the power supply is up and running.

Measure the DC voltage across ALL of the 0.1 ohm source resistors. Do any show more voltage (pulsing) than the others?

 

[Jason Smith 616]

I have the power supply up and running now.

now the issue i have is the amp like to blow outputs..

 

[Perry Babin]

Power up through a current limiter.

 

[Jason Smith 616]

This amp uses FQA36P15 and FQA28N15 as the outputs .

For testing only can i use the FQA36P15 and FQA46N15 or will this give me problems?

 

[Perry Babin]

It should not.

Are all of the gate resistors within tolerance?

Are you sure the bias isn't set too high?

 

[Jason Smith 616]

I just realized that i forgot to turn the bias pot fully counter clockwise i just did and i will install the outputs and see if the amp works

 

[Jason Smith 616]

replaced the outputs now i have full rail voltage across the output terminals

 

[Perry Babin]

Are the outputs in the correct locations? It has parallel output pairs but they're not together. There is a 28/36 then around the back, anotrher 28/36.

 

[Jason Smith 616]

I have the 36P15's on the positive rail - Q2012,Q2010 locations

and have the 28P15's on negative rail -Q2011,Q2009

 

[Perry Babin]

28N? If so, that's right and you're back to checking the smaller components.

It's odd that it was drawing current with the bias up before. Does setting the bias higher increase the idle current now?