Hi everyone. I am currently working on a Rockford Fosgate Punch 250m2. The Amp powers up and the right channel plays as it should. The left channel however, is having some issues. If I run the Amp below 11.8v, the left channel will play loud and clear. If I raise the input voltage above 11.8v, i am only able to get roughly 10 watts out of the left channel before it starts to distort very badly. However, under no load the left channel produces a clean sine wave at all input voltages. I can't seem to find any obviously dead components on the board, so I was curious if anyone else has ever seen a similar fault. Thank you.
Photo of the distorted waveform driving a load (preferably a dummy load)?
If the amp is playing normally up to full power under 11.8v and you increase the voltage slightly, does the channel immediately drop to 10 watts output?
Does the voltage across R302 change as it goes distorted?
Does the input to C301 always remain clean?
If the amp is playing normally up to full power under 11.8v and you increase the voltage slightly, does the channel immediately drop to 10 watts output?
Does the voltage across R302 change as it goes distorted?
Does the input to C301 always remain clean?
Hi Perry, I will post a photo of the waveform and get those measurements for you later today. If the Amp is playing normally at 11.8v, and I slowly increase voltage, the audio output will begin to distort badly. As soon as I back the voltage down to 11.8v it will play clean again. Here is a link to a short video of what it's doing. In the video I am play a 40hz tone. The Amp is running at 12.5v. Once the gain goes past 1/4, it begins to distort. My signal voltage is very low as well. On this same setup I am able to turn the gain on the right channel all the way up without the Amp distorting.
Hi Perry, the photo below is a picture of the output wave with an input voltage of 11.5v
The photo below is with the input voltage turned up to 11.8v. I had to raise the voltage divide to see it properly.
When the sine wave is clean, the voltage across R302 is 3.74vdc, when distorted, it is 3.83vdc. The input of C301 has a bit of noise on it, but shows a 40hz sine wave while the amps output is clean and distorted. Thank you.
The photo below is with the input voltage turned up to 11.8v. I had to raise the voltage divide to see it properly.
When the sine wave is clean, the voltage across R302 is 3.74vdc, when distorted, it is 3.83vdc. The input of C301 has a bit of noise on it, but shows a 40hz sine wave while the amps output is clean and distorted. Thank you.
The other channel has a separate gain. That channel functions as it should regardless of input voltage. And at 11.5v it will produce full rail-rail output. The second I go above 11.8v that +/-3v sine wave gets dirty.
I'm not sure what you are referring to as the bridging terminal. And I already went through and cleaned all the switches. No issues there.
Does the bias pot control the bias of the channel above and below 11.8v?
Does it have the ability to force the idle current as high as the bias pot in the other channel?
If you ground your scope to the non-bridging terminal of the channel, you're likely to get cleaner signals.
Are you sure that the replacement 0.1 source resistors are the correct value?
Does it have the ability to force the idle current as high as the bias pot in the other channel?
If you ground your scope to the non-bridging terminal of the channel, you're likely to get cleaner signals.
Are you sure that the replacement 0.1 source resistors are the correct value?
Thank you very much for you help Perry. I heard some arcing under one of the rail caps upon power up. I removed the cap and saw that it wasn't making a good connection to the top trace on the board. Looks like the via was damaged from a previous repair or recap. I repaired the via, reinstalled the cap, and everything functions as it should now. It looks like the power supply begins to regulate at 11.8v, so I see why it was cutting out when the power supply duty cycle was lower. I appreciate the help and suggestions.
