Allen and heath zed fx16 no main output

[Chadk88]

My Allen and heath mixer main l and r main outputs have stopped working. I have checked all of the aux outputs and everything else and they seem to be working. Is there anything specific I should check. I am fairly new to working on my own stuff, so any help would be greatly appreciated. Thanks

[52 Bill]

Welcome to the place.

It would be helpful to you and to all of us here if you had a copy of the service manual or at least the schematic for your unit in order for us to communicate on an equal basis.

If you have one, post it here. If you don't, then maybe someone here will have one to share.

Again, Welcome.

[Jazz P Bass]

See if you have signal at the Mono output.

You can also check if you have a signal at the L/R insert jacks.

This may help narrow down the problem.

There is a block diagram in the manual that may help in the signal tracing:
http://www.allen-heath.com/media/AP7...6FX_22FXUG.pdf

[mozwell]

I cant find any on line schematics for this, but allen & heath have a lot of info on "old" units on their web page
GL3 or these others may be similar enough
GL3 - Allen & Heath
http://www.allen-heath.com/ahproduct...rd3-16-2/#tab4
http://www.allen-heath.com/ahproduct...x-12-2dx/#tab4
http://www.allen-heath.com/ahproducts/pa12-cp/#tab4

Check you are getting power supply to the op amps on the master board
Check all connectors are plugged in & one hasn't come loose
It would seem unlikely that both L & R inserts have gone weird, if you have an insert lead, try it, or use a stereo lead & short together tip & ring to "bypass" the insert socket

[Enzo]

When I hear both mains are out, other than a connector off, my first reaction is some makers put dual op amps between the L and R sections and the op amp is shared by the two channels, so one defective op amp can kill two outputs.


nickb has a lot of A&H on his web site, I have no idea which, if any, are close to yours, but add those to what mozwell posted.

Guitar Amplifier Schematics and more

[km6xz]

I have schematics for many models but not a ZED FX series, lots of ZED's however.
So you have checked routing so all aux sends, send and all CR monitor output is OK. What about the Mono main buss output? It sums the R and L mains before the fader and inserts.
Do the Main L&R section inserts send a signal to the tip of a TRS plugged into the main inserts?
When a whole section is not working that is on multiple boards the first thing to assume is routing error since the Right main and Left Main are on 2 separate circuit boards and they share the power supply with the channel strips, and you say they work.
That comes down to mute switches, mute logic, or routing, or the ribbon cable for the master section came loose.
If you don't have a scope, you can plug in TRS headphones into the inserts for the Mono, Left an Right Mains and your should be able to see the expected signal if the signal is getting to the inserts. The mains mutes are post fader so inserts will still be hot even if they are muted.
Are all expected indicator LEDs light in the master section? Do the LED meters display a signal?

[The Dude]

......You can also check if you have a signal at the L/R insert jacks.

This may help narrow down the problem.......

^^^^^^ That! You can plug a 1/4" mono cable in just to the first click and see if anything comes out. It could be the insert jacks themselves. If not, it will at least tell you if the problem is pre or post insert jack.

[Chadk88]

Ok here's what I have so far. The l and r inserts are showing a signal but the mono out and the headphones are not. I made sure nothing was muted and the signal was going to main out. It is metering when I have aux button or the pfl button engaged, but when I switch to the main out It stops metering. Also, I do have a signal through the phones when it is in aux.

[Chadk88]

One other thing, when I had the unit on checking things it powered down a turned back on by itself, so I wiggled the cord when it turned back on and it did the same thing

[Jazz P Bass]

Ok here's what I have so far. The l and r inserts are showing a signal but the mono out and the headphones are not. I made sure nothing was muted and the signal was going to main out. It is metering when I have aux button or the pfl button engaged, but when I switch to the main out It stops metering. Also, I do have a signal through the phones when it is in aux.

There is something wrong with the Main Insert jacks.

Insert a TRS (stereo) plug in one & try jumpering the Tip & Ring.

[Chadk88]

There is something wrong with the Main Insert jacks.

Insert a TRS (stereo) plug in one & try jumpering the Tip & Ring.

What exactly do you mean by jumpering the tip and ring, bit of a newbie. And even if the main jacks are bad wouldn't it still meter

[oc disorder]

Allow me ! An example of a jumper is a kangaroo.
My apologies ChadK 88 , without humor some of the older members think they can run for president
and it takes years and years to convince them otherwise!

In this instance "to jumper"
a short wire to close a break in, or cut out part of, a circuit, or to make a temporary electrical connection

some related info on TRS jacks

Understanding TRRS and Audio Jacks - Cable Chick Blog

Insert point on block diagram JPBass mentioned .


The insert point on your mixer allows the signal path to be broken so an effect can be "inserted" into the signal or audio path.

Usually it comes in the form of send and return which takes up two jack hole spaces in the mixer. In this instance by using a tip , ring and sleeve jack (a 3 wire circuit same plug as stereo headphones for example) both the audio/signal coming out of the mixer and the input for it to go back in) , are in the one housing and only one hole is required in the chassis !

So to plug a graphic equalizer in there for example you have to have a special "Y" looking kinda lead.

Page 15 mentions an insert point in the manual.

If any grit or dust gets in there , that is the switch part when the insert jack is pulled out the signal can't get through.

If you look closely at the block diagram section I posted above you can see that when a jack is pushed in
to the insert jack, the ring connection would move down breaking the connection with the switch contact which is connected to the tip.

Sometimes firmly pushing and pulling a jack in and out will clear the grunge on the shiny metal terminals.

Otherwise a good cleaning solvent like Caig Deoxit is required.

So what JPBass is suggesting is to solder a wire between the tip and the ring of a TRS jack so when pushed in
it takes over the switch role in the TRS jack socket and connects together the tip and ring.

[Jazz P Bass]

Very well put, OC.

[oc disorder]

pleasure .. here's a complete jumper!

[Chadk88]

I did take the power supply and found the power plug was loose and had three broken solders, would that have anything to do with it