Rockford Fosgate Punch 75.2 static channel - diyAudio
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Old 20th January 2011, 05:43 AM   #1
chipper is offline chipper  United States
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Default Rockford Fosgate Punch 75.2 static channel

I recently replaced one channel of output FETs and haven't tested my work since until now when i plugged the amp in the output sounds really distorted, like a radio that has no reception. I measured the resistance on the source resistors and those are good and the gate resistors all checked fine. Anyone have an idea whats causing this noise?


Note: when i put my finger on the driver transistor (to drive IRF540) it sounded alittle cleaner but went back to horrible when i took my finger off.

leaky capacitor, out of tolorence resistor, broken trace somewhere??
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Old 20th January 2011, 05:17 PM   #2
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Does the other channel produce clean audio?
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Old 20th January 2011, 05:48 PM   #3
chipper is offline chipper  United States
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Quote:
Originally Posted by Perry Babin View Post
Does the other channel produce clean audio?
Yes it does. Could it be a open trace?
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Old 20th January 2011, 06:01 PM   #4
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It could be almost anything.

Do you read ~0 ohms between the RCA shields of the amp? Push back on the terminals gently while measuring the resistance. Have no RCAs plugged into the amp when measuring the resistance.

If you read 0 ohms, please post a photo of the inside of the amp?

Do you have a scope?
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Old 29th January 2011, 06:45 PM   #5
chipper is offline chipper  United States
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MPSA56, i don't think its connected or something that feeds it is probably broken or open? I disconnected MPSA06 and no audio. Is there a muting transistor of some sort?
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Old 29th January 2011, 10:15 PM   #6
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Is this a reply to a question for this repair?
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Old 29th January 2011, 11:15 PM   #7
m4ick is offline m4ick  United States
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He is thinking he has a similar problem to mine with the MA audio amp.

Drive a signal through your amp and show Perry what it looks like when it distorts and where inside the amp it begins to distort, at least as far as you can tell.

chipper, my muting transistor was "leaking" not shorted, it's pretty difficult to detect a "leaky" transistor without the help of..... "certain" others.
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Last edited by m4ick; 29th January 2011 at 11:18 PM.
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Old 30th January 2011, 09:52 AM   #8
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Hey chipper what’s going on man! Stay persistent you will get it figured out. You can do a lot of checks & tests with your multi-meter.

My only suggestion is if you’re not sure where to begin, listen to Perry Babin & check what he asks you to check if you have the tools to do so, you can slowly work your way into the circuit to find the problem. He really knows his stuff when it comes to electronics & amp repair & he has walked a lot of people through there repairs here on the forum over the years & is very knowledgeable on amplifiers.

I did not mean to clutter up your thread, just wanted to say hey, & don’t give up, you will get it working, sometimes you just got to be patient.

Take it easy!
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