Kicker KX850.4 weird input issue

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Hi all, I just bought a Kicker KX850.4 locally and when I brought it home, I bench tested the amp. All works or at least appears to be fine. There is one issue (I guess this is an issue) where when the low inputs (RCAs) are plugged into the amp only on amp1, channels 1/2, they could send output to all 4 channels. When I then tried to send input into amp2, channels 3/4, there was no output from channels 3/4 and if there was a signal into amp1 as well, channels 3/4 would have no output.

I read in the users manual that you could use only one pair of RCAs to supply input signal to power all four channels but this seems a bit strange to me. This amp does not have a switch (at least I believe so) that could switch between the inputs and fader between amp1 and amp2 so I am left confused.

This is the 2004 model with the silver cover and EndKaps (as Kicker called them.) the amp has not had any repairs done to it. Thanks in advance for the help!
In some of the kicker amps, there are switches built into the RCA jacks. When you feed 3 and 4, it breaks the connection to 1 and 2. In some of the amps, the ground is lost when feeding 3 and 4 alone and the amp won't function properly unless the 3/4 shields are shorted to the 1/2 shields. When all 4 channels are fed with normal RCA signals, all 4 channels should function.

On one of the preamp boards, there is a trace that burns just as it goes under the 3/4 input side of the RCA jacks.

If none of that helps, papaZBill may be here later.
Just so I understand you, when you have signal applied to both sets of RCA'S, you have no output correct?

Only when you apply signal to the front left and right channel inputs you have output and on all four channels, correct?

I will examine schematics tommorow and get back to you.

You may won't to examine the RCA terminals closely, to see if the switches look deformed or otherwise damaged. Other than open traces, cold solder joints or the RCA'S themselves could cause the problem you are describing, that comes to mind.
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