no stereo output from the desk ,only mono ...need a repair Tutorial

Hi guys, I have a Behringer Xenyx 1222 FX mixing desk that I use for micing up my drum kit in the band I play for , all was fine until a while back , when I lent it out to a close friend to use as a vocal p.a desk for an acoustic jam session he orgonised ,and he called me later that day telling me there was no stereo output from the desk ,only Mono , but the headphones get stereo nothing had been muted on the desk either ..... hmmmm ????? . I bought the desk used from a good drummer buddy of mine , who used the desk for his drum kit and D.J work , and I made sure everything tested fine before I purchased it , I gigged it twice with no problems, until I lent it to my friend - who is the singer and guitarist in our band ( and he is always very careful with ,and respectful of other peoples stuff if he borrows it ) I have a feeling its either the output jack socket or a circuit board problem ....I have no idea at all really ,but would really appreciate it if anyone could either help with a visual tutorial ,or provide a link to a good tutorial please . its a great little desk , everything works on all channels including the effects , apart from just one thing .... no stereo out ! :( to my knowledge , it has never been dropped or bashed about ,and is always in its split flight case . if anyone can please help me here , that would be awesome :)


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thanks so much :)


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Here is a circuit diagram of the relevant part of the mixer.

Block Image

Depending on whether the left channel or the right channel is missing on the output will mean which part of the circuit you need to look at.

As you say the the headphones are working in stereo, it proves that the problem is somewhere in the Main Mix amplifier section. As seen on the circuit, the headphone's sound is taken from the inputs to the Main Mix amps. (Phone_L and Phone_R at Main Mix points VR79A and VR80A to be fed into the Phones_Ctrl at R387 and R388 and then onto the headphones socket).

So you need to work back from X9 socket (or X10 depending on which is missing) to VR79A (or VR80A) to see where the problem lies. Start with the socket first, it may be as simple as a wire broken off or a loose connection

Hopefully this is of some help.

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