Behringer SL2442FX-PRO > Trouble shooting Main Outputs....

[Twistedpair]

I just bought a used SL2442FX-PRO and found that the Left main output is not working and the right main is working but sounds very distorted. My connection cables and amplifier are all ok. I used 1/4" TS plugs in the main out jacks, was this ok, as the users manual simply stated that the Main out jacks was a TRS and that if a TRS plug was used, the ring and sleeve had to be bridged. Did the TS plug I used make that bridge connection ?

[Enzo]

Yes, a TS plug grounds the ring to the sleeve.

Check the main fader itself.

Also, I think there are a bunch of patch jacks, try the insert jacks for the main outs

[Twistedpair]

Use a TS in the Main Insert Ok ?

[Twistedpair]

Tried the Main inserts using the TS plug with no output, just buzzing. Also, I noticed that the main fader does not control the Left and Right led bar graph. When the main fader is pulled down, the led bar graph is still showing a signal coming thru and when the fader is pushed up, it still shows the signal coming thru with no increase in the signal. How can I check the main fader ? Thanks....

[Enzo]

An insert jack is just like an effects loop, except it is one jack. The tip is the send, and the ring is the return.

With signal applied to some input channel, center panned, and main faders up, plugging into an insert all the way gets you the tip, and there should be a signal there, which you can listen to at some other amplifier. You either have signal at both or neither or just one of them.

And you can take a signal from somewhere, and plug into an insert jack halfway, until you feel that first bump - that is the ring contact. In a working system, that should send the signal on through the final stages and out the main out jacks.

The mixer has a MONO out jack up there. The MAin L and R signals are taken right before the main fader and mixed together for that MONO signal. Connect the Mono out to some amp for a listen. Got sound? Now go to the input channel you are using, and pan left and right. If the Mono signal stays both ways, then both L and R are making it as far as the main faders, but if panning one direction loses the signal , then it is not getting that far.

How to check the main fader? Power off, set the fader midway. Use an ohm meter to check the resistance of the slider strip, then for resistance from the wiper to the ends. The other side of it works, so compare the two halves of the slider. Alternatively, apply signal panned center, scope the top ends of the two halves of the main fader. Got signal at both? Then check the wiper, got signal?

[Twistedpair]

Roger that Enzo. I did a few checks and found that there is no output at the mono jack, just buzzing....I have output at the Aux send jacks Left and Right....I have a very weak signal with buzzing on the Left and Right Main Out jacks with the main fader and channel fader pushed to the top....I also found that with the mixers power supply off, and with my external power amplifier on, and the input cables of the amplifier connected to the main out jacks on the mixer, I had a audible buzzing coming through the main speakers. Sounds like an internal mixer problem for sure. Guess it's time to take this thing apart and do a few checks, like on the main fader as you suggested. By the way, I did talk to the guy I got the mixer from and he said that he thought that there was a problem in the main output section and that it was probably due to something getting hooked up wrong, but he wasn't really sure. Thanks for your help Enzo....

[Twistedpair]

Ok, I've taken the bottom panel off the the mixer and found a white powder substance around alot of the componants, mainly found on the main board and it seems to be above the conformal coating on the board as I can remove this powder with my fingernail. Could this be part of my problem and what is this white powder, corrosion maybe ? Is this the remains of a spilled drink or something ? Thanks for your help....

[Twistedpair]

Ok here is a picture of the white powder on the main Board....

[Twistedpair]

Trying to check the main fader while still soldered to the board. Should I be getting a resistance reading on the two center pins ? When I check the resistance on the two pins on the left then the two pins on the right, I get a varying resistance from 6.2 ohms (fader pulled down), and 7K (fader pushed up). I also get the same reading on the two center pins of the fader. Is this normal ? Is this the correct way to check the fader ? Should'nt the two fader strips be independant of each other ? Thanks for your help....

[Enzo]

Oh the white crap is normal.

Are there not four pins at one end of the fader and two at the other? It is a single dual section fader, right? Center pins? Some faders have a couple pins along the center just to solder the frame down, nothing electrical there. Is that what you refer to?


it is a "stereo" fader. I expect the two sides to read similarly as I run the thing up and down. One end of the stripe goes to ground, and the other end takes the signal from the insert jack. The wiper passes along the desired amount.

Did we ever get a difinitive answer about the insert jack and if signal is on the "first bump"?

[Twistedpair]

Hello Enzo, Yes, there are four pins on one end of the single dual fader and two on the other end, I didnt see the other two pins until you mentioned it. For some reason I was thinking that the strips terminated back at the lower end of the fader where the four pins are located. The two center pins I was refering to was the two inboard pins on the four pin row and not the mounting tabs for for the fader. Can you explain how to check the fader again ? Regarding the insert jacks, I have output on the aux send jacks 1 & 2.... On the main out jacks with the main fader pushed all the way up, and a high channel input signal I have a very weak signal (Barely audible) with buzzing. On the mono jack all I have is buzzing....On the main insert Left and Right Jacks all I have is buzzing....Thanks for your help Enzo....

[Enzo]

Not the aux sends, there should be jacks marked something like main out insert. Oh, I see you did find them. If all you have is buzzing, are we at that half-way notch in the jacks? And checking the other half, if you apply a signal to the main insert jacks does it then come out the main outs? To input the inserts, plug all the way in for the tip contact. The main fader would control that level too.

Does it matter if the graphic EQ is switched in or out? How about TAPE OUT, is there clean signal there? Probably not a strong signal there.

IC53 is common to both L and R after the subs and before the GEQ. IC44 comes out of the GEQ feeding the inserts.

[Twistedpair]

On the main insert jacks I should go back and check that again. I need to make up a few 1/4"cables as all I have been using for a signal input is a microphone connected to a channel input on the XLR jack and a input signal connected to the RCA CD/TAPE input. Should the cables I'm about to make be TS or TRS ? On the main out jacks I tried both half-way and fully inserted with a TS plug with the same result (buzzing). Regarding the EQ in or out and the tape out checks, I haven't done that yet. I have the main board out also so I will need to re-install that before I can proceed with further testing. I will post a picture of the mixers main section shortly so you can see what I have....Thanks again for your help Enzo....

[Twistedpair]

Here is the picture showing the main side of the mixer. I know you already know this board well, but I thought that you would like to see this. Thanks....

[Enzo]

I just use plain old guitar cords. Any 1/4" jack that is balanced will also work unbalanced when a TS is plugged into it The insert jacks are TRS, but by carefully plugging in half way, a regular cord is close enough.


A plain old cord stuck into anything that is an output should be listenable in some other amp and speaker. And most any line signal is fine for testing. I just use a line out from the back of my little Technics stereo receiver on the shelf. A CD player would be fine too.

We are loking for divide and conquer points. The inserts coming out tell youy if signal is present there or not. If the insertes are noting but hum, then there won;t be anything on the main outs either. And by injecting signal at teh insert, we can test the remaining circuit between insert poi9nt and main out jack. Those other things I mentioned are farther back.