rockford fosgate power 300 mosfet

[mike49504]

Im working on this amp and wondering what the outputs are for this??

There are 9540's in the outputs but the other ones that are in there right now are irf542's arent they suppose to be the 540's??

 

[Perry Babin]

The IRF542s are likely the originals but the 540 would be what I'd use as a replacement. The schematic lists the 12p10 and 18n10 as the outputs but I think the 542 and 9540 superseded those parts.

 

[mike49504]

Ok back to working on this amp i have 3 out of the 4 channels working perfect.

Now the front left channel has problems.

when you connect the speaker wires up the speaker pops and no sound.
so I checked the 540 and 9540 they check fine. I replaced the 2 gate resistors in that channel.

I checked the drivers for that channel and they test fine wondering where i go from here

 

[Perry Babin]

What is the DC voltage on the two outputs in that channel?

540
Leg 1:
Leg 2:
Leg 3:

9540
Leg 1:
Leg 2:
Leg 3:

 

[mike49504]

540
Leg1= -11.27

Leg2= -24.36

leg3= -24.36

9540

Leg1= 26.31

leg2= 24.36

leg3= 26.32

 

[Perry Babin]

What's the DC voltage on the LM833 for that channel?

Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:

What is the color of the speaker wire for this channel?

 

[mike49504]

i checked all the op-amps since i cant figure out which one goes to that channel all read the same beside one of them

and that one reads 0 volts on the first three legs of it

 

[Perry Babin]

What is the color of the speaker wire for this channel?

 

[mike49504]

its the front left channel and the wire is white

 

[Perry Babin]

It appears that there may be more than one problem.

There's a Zener diode connected to the output of the op-amp. Is it shorted?

There's a 56k (maybe 56.2k) ohm resistor that's used for feedback. One end is connected to the white wire. The other end to pin 2 of the op-amp. Is that resistor within tolerance?

Are those two connections intact?

 

[mike49504]

resistor reade 56.1 and the diode checks fine

 

[Perry Babin]

Are the connections between the resistor and the wire/op-amp intact?

 

[mike49504]

everything is connected i tested that op-amp with the right channels that work and i get the same reading on both opamps.

so now i have to dig a lil deeper into that channel to figure out why it doesnt work

 

[Perry Babin]

The op-amp should have at least 1/2v on pin 2. If the op-amp had a connection to ground, it would be possible that a shorted op-amp could be causing the voltage on all 3 pins to be at 0v but there's no connection to ground.

Is the voltage on pins 1, 2 and 3 precisely 0.00v DC?

There are two other diodes connected to pin 2. Is either shorted?

Are there any solder bridges on or near the op-amp?

 

[mike49504]

The op amp that controls the front left channel and the rear left channel reads

pin1= 0.96

pin2= 0

pin3=0

pin4= -18.18

pin5= 0.97

pin6= 1.14

pin7= 0.87

pin8= 18.18


theres another op amp more towards the RCA's and the first 3 legs of it are 0 volts

 

[Perry Babin]

To clarify, this op-amp (see attached) is the one you've just posted the voltages on?

 

[mike49504]

yes this is the one im talking about i i replaced the two diodes that are circled 1n4148 and on pin2 reads -0.22

 

[Perry Babin]

Post the voltages on pins 1-3 again.

 

[mike49504]

Pin 1= -1.00

Pin2= -0.90

Pin3= 0.00

 

[Perry Babin]

The op-amp appears to be defective.

With the inverting input at a lower voltage than the non-inverting input, the output should be positive.