The effects will not work for more than 10 or so min, then quites

Check the inserts and pan controls.

go to this site and call http://www.prosoundservice.com/
they will get you what you need good luck

I assume you mean the wall wart power supply and not the actualy internal power supply in the board...either way check out Full Compass Pro Audio Video Lighting Equipment Largest Microphone Dealer... or better yet www.prosoundservice.com for your needs ..they can help you out... good luck http://www.prosoundservice.com/

http://www.prosoundservice.com/

Yes, but it could be pointless.
Headphones are just small speakers so it is usually possible to drive a small pair of "computer/iPod" type speakers from the headphone output.
True balanced outputs should have a fair amount of drive so try connecting a speaker between pins 2 and 3. The higher the impedance of the speakers the better.
Ultimately, the results will be very quiet and the cost of a small amp or powered speakers for low level use is quite reasonable.

check it out here.. SOUNDCRAFT EFX12 EFX8 MIXER Service Manual free download schematics eeprom...

circuit diagram for soundcraft efx 12 mixer

Effects plug into mixer, mixer plugs into power amp. Others may want the mixer and the effects plugged into the power amp for the most available inputs. (when multiple inputs are available.)

Effects and mixer are a line level output and the mixer can be considered a line level input as well. A mic mixer has gain amplifiers for the inputs that are below line level such as unamplied microphones. It is possible to parse to absurdity, but the gist of it is above assuming you do not want to apply the same effects to everything all at once.

USUALLY the Mute LED's for the switches ar operated by separate contacts on the mute switch an a resistor current limit for the LED. I could NOT find the schematic for this board, HOWEVER some Soundcraft brand mixers do NOT have illuminated Mute switches... Not sure about your particular unit.

If the LED's are level indicators, you are probably saturating the input of the effect and may cause it to hang. Effects use delay and feedback and can cause numerical overflow and the system to basically crash. I would first call the Lexicon support and ask them about this problem... I did have to return one Lexicon product myself for service under warranty.