Weird mixer problem

[aardvark5]

We've got a Soundcraft FX16 (mk1) mixer that has been faultless for 10 years.
Last night I set it up, tested the mic and it was muddy.
I turned the treble pot and nothing happened.
Turned the mid and bass and they were OK.
All channels wouldn't work with the treble pot so I'm thinking the treble rail has gone down on the mixer.
After 90 mins of messing about we had to go on and play so I plugged the monitor amp into Aux1 and all of a sudden the PA came back to life and I could use the treble pots.
I took the lead out of Aux1 (or 2 and 3) and the PA went muddy again and I couldn't use the treble.

Anybody got any ideas whats going on here?

 

[mixsit]

..I plugged the monitor amp into Aux1 and all of a sudden the PA came back to life and I could use the treble pots.
I took the lead out of Aux1 (or 2 and 3) and the PA went muddy again and I couldn't use the treble.

In other words, the main out only sounds normal when an aux/monitor is also plugged in, or you're shifting the output around from mains to aux's?
Just curious, not sure what to make of it either way though.

 

[Whale Bone]

Are you sure the highs reappeared in the PA and not just the monitors, i.e. the main PA amp or cabinets are not delivering highs due to a amp, speaker or crossover fault?

If you connect the mains through the aux sends, are the highs there?

Does it make a difference whether you are using a pre or post aux? If a post aux (or pre fader/post EQ, if available) delivers full sound, then the EQ section of your input is at least OK. And if the mains are truely corrected by connecting the monitors, then the EQ in the master section is presumably OK, too.

If connecting your monitors to the auxes really is what's required to make the main outs deliver proper sound, then perhaps your main buss cable from the channel strips to the master section isn't conducting its ground properly, and by connecting the monitors you are completing a ground connection? Sounds crackpot, but I can't think of any other reason for that behavior. Is the problem on all inputs? If you try the input closest to the master section, i.e. less cable to travel, is it OK or better?

Do the sub outs work properly on their own? You don't have the subs and the mains assigned and reversed left and right? Not sure if you can pan the subs independently, such that if you had the sub 1 panned right and feeding main 1 which was the left signal, etc. On my 200B I can actually do this (not the sort of thing you'd do by mistake), but I'm not sure if you can on the FX16. Combined with a stereo reverb or something, I suppose it could cancel sound, until you added the monitor sound to reduce the cancellation. It seems even more unlikely than my last idea... enough.

Failing all this, you might try posting here:
http://forum.analogconsole.com/viewforum.php?f=25
This forum is moderated by a former Soundcraft designer, Gareth Connor, who's very helpful.

 

[aardvark5]

It wasn't the sound of the monitors effecting the main sound because I turned the volume down on them.
Jack plug out = muddy sound, jack plug in = normal sound.
I tried every button, knob, switch a dozen times over with no joy.
Tis a weird one.

I'll try that other site - thanks

 

[Whale Bone]

Is the muddy sound on every input channel?

Have you tried the Sub out instead on the main?

Have you tried the channels' direct outs alone (no mains or aux connections)?

I would try this:
Connect a male to male TRS cable to the aux out and another one to the your monitor amp. With your monitor amp's volume down, connect the shields then tips then rings of the monitor input cable to the aux out cable and see which one or which combination of connections makes the mains sound clear. The only thing I can imagine it is would be the ground, but...

 

[SonicAlbert]

I don't have any specific advice, but I would suggest testing your mixer in another environment before getting too worried. In other words, test it with a different monitoring system at a different location. If the same problem persists, then you have some troubleshooting to do.

That said, it sounds like something died inside the mixer (like a component, not a small rodent).