I'm troubleshooting a stereo for a friend. I've never seen this problem before...

here are the symptoms.

The amp worked intermittently for a while. Then it pretty much quit, and that's where I came in. The amp was clearly on and working to some extent (speakers were vibrating a little... but nothing like they were suppossed to be).

I started with the ground and power wires, and everything is solid. I even checked fuses. All are fine.

I then checled the RCA cables... this is where the unfamiliar symptoms start...

I can hook up eather RCA cable to either RCA input and I would get sound- but ONLY if only one was hooked up). It seemed to work normally, with both speakers working (they are bridged at amp).

For troubleshooting, I put in a known good pair of speakers in a box: Here are the results;

(well, first off) It is a stereo amp (a Kicker 150.2) with standard inputs/outputs R and L RCA inputs and right + and - and Left + and - speaker output. It also has right and left RCA outputs that aren't being used.

With the left and right speakers hooked up separately (not bridged), both speakers work... BUT, when I unhook one RCA cable I get about a 10 dB increase in volume (from 92 to 102), even though only one speaker is on. The same is for each speaker. Same loudness regardless.

When bridged, there is basically no sound from either speaker if both RCA's are plugged in. If I remove either I get sound from both speakers. However... it is 6 dB louder than the loudest from above. (108, instead of 102). But, of course, even that seems... quiet.

I was using sine waves of one frequency, to take out as many variables as possible. It was measured from atop the center console with all doors open.

What else should I try?

Any ideas on what might be wrong?

I'm guessing there is something up with the amp. maybe a short in the rca inputs?
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Master Yoda
It sounds like you do have a short in the RCA inputs. it seems that you have tried almost everything but switching out amps i would try that next.
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is he running an after market deck with preouts or a line out converter. if its a converter the speaker leads into it could be out of phase. It could also be the deck is bad. I would also try another pair of rca's.
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bad rec.bridge?
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rec. bridge?

I've done a couple more things...

I don't know how it is hooked up to the hu. It is an F-150 ('03 I think, but I'll check if you want). I'm guessing it has RCA outs, as it is a 6-CD-changer model... but not sure. I din't feel like taking it apart, so I dug up a bass CD that has an out-of-phase track. Same symptoms. So that probably rules out phase issues.

I'll try to hook up another amp like you mentioned later and see what happens. that could rule out amp issues.

I'm also going to bring out a home CD changer because I know there are no RCA issues with it. That should rule out the HU and HU RCA's.
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if that is the factory radio in the truck then it absolutely does not have rca's on the back of it.in which case it has a line output converter in as B_runz said the speaker leads are out of phase just switch two of the same color leads around doesnt matter which at this point and all problems should be solved.
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Check to see that the positive and negatives are right in the box. Sounds like a problem i had once and it was that. Hope you figure it out and it's something simple.
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I swapped out the amp and another set of speakers as well and all symptoms are the same. I even used an external battery to test as well. I've tested with test tracks that go from left to right, normal music tracks, and tracks in different phases and no matter what, if both RCA plugs are connected, the signal is very reduced.

So that means it's narrowed down to somethine in the HU, RCA cables, or convertor.

The main culprit atm is a little box that says it is a noise reducer and sth else... guessing it is that device some of you mentioned that converted speaker outs to RCA outs. There are two wires that are each crimped to two wires going into the box. I'm going to check it for shorts (if I can get it open without destroying it ).
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