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Dr Zeus 20th January 2012 02:47 AM

Rockford Punch P4004
I've got this amp in which has a chasing problem. The thermal light was flickering, but only while the LED board was connected. While flickering, the amp would not power correctly. With the board disconnected, the amp powers with good rail voltage and plays across all channels. I then re-connected the board, and read that flickering P series thermal LEDs may have to do with grounds; so i ground the RCA shields to amp ground as a temporary step. Amp played, but now anything I try will not flicker the thermal LED.

The LED board also doesnt work the way it should. Its supposed to light up the Rockford logo, yet it doesnt. I found 12vDC on Pin one of TL072C opAmp at U3 so i replaced it. The new unit does not have significant DC on pin 1, but the LED board still doesnt work - it works the same as with the defect opAmp. The LM339 is working OK, and on all output pins is measuring +11.4vDC (Signifying all + inputs are greater than - inputs).

Sometimes when I power the amp off, a couple of the LEDs light and fade quickly.

This LED board appears to maybe be missing a resistor, R12 next to the opAmp. Does anyone know it's potential value? Voltage on the pads is 14.3dc and 0.5dc.

I have not taken this amp completely out of the sync so I dont know what may have happened if anything under the board. i dont want to risk causing more problems if the only problems are with the LED board.

Dr Zeus 20th January 2012 03:21 AM

You know somehting, I think all this amp needed was U3 TL072c opAmp. I didnt realize that this LED board actually only activates with an input source. The more input voltage or gain, the more light the LED board emits through the Rockford logo.

This amp wasnt working at all with this LED board connected before, so; replacing the opAmp fixed it?

I also want to point out that from the factory, this amp was missing the following screw which could have caused transistor failure. Photo center.

Perry Babin 20th January 2012 03:24 AM

Have you pulled the main board to see if there were any burned traces?

If the LED board is PC-5124-A, R12 is not installed.

Dr Zeus 20th January 2012 03:35 AM

I just lifted the board out, and no burned traces anywhere. I'll put this one back together and give it a good test-run. :)

Dr Zeus 20th January 2012 06:39 PM

I noticed each channel was biased kind of higher than normal at 0.007, so I lowered it to just below 0.001. The owner of this amp is going to run 2 subs and 6 door speakers off this thing, so hopefulyl the lowered bias will keep the dragon within.

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