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Old 1st September 2009, 07:19 AM   #1
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Default repair of rockford fosgate power 451s

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The larger 10 ohm resistor (in the middle of the zoomed picture), burns and causes that channel to distort. I replace the resistor, and the amp works again for a week, then it burns again?? I have found no other damaged parts (output transistors, diodes or other resistors). Why would this continue to overheat? What is the function of this resistor? Source resistor? The amp has a 2.6 ohm stereo load on it.

Thank you in advance for any insight.
Mark
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Old 1st September 2009, 11:26 AM   #2
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Your picture does not show up. Is it a 2 watt resistor? Is one leg of the resistor connected directly to one of the output transistors? Is there one resistor per output transistor? If you answered yes to all 3 questions, chances are the resistor is a (.)1 ohm resistor.
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Old 1st September 2009, 12:42 PM   #3
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hopefully this time the pictures work.
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Old 1st September 2009, 12:43 PM   #4
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Click the image to open in full size.

hopefully this time the pictures work.
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Old 1st September 2009, 12:45 PM   #5
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Old 1st September 2009, 03:00 PM   #6
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What is the DC voltage on the following resistors (no audio, measured directly across the resistor terminals)?

R148:
R149:
R151:

R248:
R249:
R251:
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Old 2nd September 2009, 12:27 AM   #7
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Quote:
Originally Posted by Perry Babin View Post
What is the DC voltage on the following resistors (no audio, measured directly across the resistor terminals)?

R148:
R149:
R151:

R248:
R249:
R251:
r148: 1.27v
r149: 1.173v
r151: .004v

r248: 1.31v
r249: 1.43v
r251: .004v

r151 and r251 are the resistors that are burning, and causing distortion. The others listed still read 300 ohms. There has been 2 cases where r177 also burned. Replacing these resistors fixes the problem, but I have had to do this repair several times. r151 appears to be a 10 ohm 1% 1 watt resistor, would increasing it to a 2 watt resistor help? Maybe I am just pushing it to hard or maybe I have not found the additional faulty components.

Thanks for the help.
Mark
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Old 2nd September 2009, 01:51 AM   #8
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Location: Louisiana
There's nothing there to indicate that there is a problem.

If you're driving it into hard clipping or if you're running it below 2 ohm stereo/4 ohm mono, that could be the reason that the 10 ohm resistors are overheating.
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Old 2nd September 2009, 02:51 AM   #9
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It is running at 2.66 ohms. Maybe I will rewire to a higher impedence. Thanks for the help, I am probably just driving it to hard then. I will have to do some gain adjustments and rewiring and see what happens.

Thanks again,

Mark
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Old 26th December 2009, 07:00 AM   #10
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Default Rockford Fosgate 451s Repair: Diode D7

I am repairing my 451s Amplifier. I notice that Diode D7 is burnt and cracked open. The D7 is in the vicinity of R215 and R32. I can't find the part number anywhere. Can someone please advise me so I can order accordingly.

Thanks,
Matt
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