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Old 9th August 2011, 03:15 AM   #1
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Default Rockford Fosgate T30001

Hello everyone. I recieved this t30001 in for repair. It belongs to a friend of mine. The complaint was pulsing of the speakers and low output. I have not tested it for audio myself, but will soon I have a few other amps to finish up on.

I powered it up on the bench and there is a pulsing buzzing noise from the power supply and then when the protect light goes out there is a pulsing chirping noise from the output side.

I dont know alot about this particular amp and have never worked on a amp this big.

The only thing I have done so far is tested to see if thier was DC on the output terminals and there was not.

Just wondering if someone could point me in the right direction as in where to start???

Thanks again.
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Last edited by seankane; 9th August 2011 at 03:18 AM.
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Old 9th August 2011, 03:41 AM   #2
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OK just tested for sound. The amp does produce sound but it is very distorted and you can here the pulsing chirp from the speaker and the speaker pulses in and out the whole time.

My friend did indicate he had a previous problem with the cross over frequency pot and had it replaced. Apparentely they replaced it with the wrong one and had to bring it back to replace it with the right one.

He said the amp worked good then he hooked up some new subs and hit some hard notes dropping the volt meter to 8 volts in his ride and this is when the problem occurred.

The amp does not draw excess current but pulses while idling on my power supply amp meter but not much. You can hear the pulsing buzzing on the power supply side and the pulsing chirp on the output side, I tried with and without an input signal with same result.

I tried all the knobs and switches the only thing I noticed is the gain has to be all the way up for the sound to work, if its not all you here is the pulsing chirp and staticy squeelch noise.

Hope someone can steer me in the right direction......Thanks
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Old 9th August 2011, 08:42 AM   #3
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Sounds like power supply, just a guess.
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Old 9th August 2011, 12:51 PM   #4
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Check the output pins of all of the op-amps, do any have significant DC?

Is the output filter inductor loose on the board?

Does having the subsonic filter on help?

With the black meter probe on leg 3 of Q431 and the red probe on the center leg of Q430, what is the voltage?

Does the voltage remain steady with and without driving a signal into a load?
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Old 6th January 2012, 12:15 AM   #5
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Quote:
Originally Posted by Perry Babin View Post
Check the output pins of all of the op-amps, do any have significant DC?

Is the output filter inductor loose on the board?

Does having the subsonic filter on help?

With the black meter probe on leg 3 of Q431 and the red probe on the center leg of Q430, what is the voltage?

Does the voltage remain steady with and without driving a signal into a load?
Perry getting back to this amp the last question you had asked you want me to check if the voltage is steady with or without a signal driving a load?

If so you want me to hook a load to the amp with no signal and check the voltage too? Just want to be clear.
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Old 6th January 2012, 02:13 AM   #6
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I don't think it matters if the voltage on the speaker terminal pulses without a load.
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Old 6th January 2012, 02:19 AM   #7
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Output Filter Inductor loose on the board: NO

The sub sonic switch make a difference? : NO

Black Probe to leg 3 of Q431 and Red Probe to middle leg of Q430 I get a constant 117.8 VDC

Voltage remains steady with or without signal with or without a load between the legs you wanted tested and in accordance with how you requested.

I have not checked for dc voltage on the outputs for the op-amps yet.

I believe you want pins 1 and 7 on all the TL072C'S?
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Old 6th January 2012, 02:21 AM   #8
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Yes. 1 and 7.
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Old 6th January 2012, 02:44 AM   #9
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OK Perry bare with me here........................

U304

Pin 1: 2.171 vdc
Pin 7: -4.35 vdc and when tested makes amp go into protection

U306

Pin 7: -1.679 vdc

U307

Has no significant DC but testing pin 7 makes the amp go into protect.

All of the other op-amps have no more than 0.635 vdc on pins 1 and 7.

Thoughts????? Sounds like I may have a defective op-amp????
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Old 6th January 2012, 02:51 AM   #10
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Post the voltage on all pins of U304 and pins 5, 6 and 7 of U306. Set the subsonic switch on. That should help prevent it from going into protect.

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

Pin 5:
Pin 6:
Pin 7:
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