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Old 20th December 2009, 02:26 AM   #1
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Default rockford fosgate power 300 mosfet

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??
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Old 20th December 2009, 02:58 AM   #2
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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 The schematic lists the 12p10 and 18n10 as the outputs but I think the 542 and 9540 superseded those parts.
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Old 22nd December 2009, 10:23 PM   #3
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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
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Old 22nd December 2009, 11:27 PM   #4
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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:
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Old 23rd December 2009, 12:42 AM   #5
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540
Leg1= -11.27

Leg2= -24.36

leg3= -24.36

9540

Leg1= 26.31

leg2= 24.36

leg3= 26.32
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Old 23rd December 2009, 12:47 AM   #6
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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?
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Old 23rd December 2009, 01:18 AM   #7
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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
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Old 23rd December 2009, 01:20 AM   #8
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What is the color of the speaker wire for this channel?
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Old 23rd December 2009, 01:22 AM   #9
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its the front left channel and the wire is white
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Old 23rd December 2009, 01:34 AM   #10
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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?
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