No audio from main speakon outputs A and B

Need more info, how many main speakers and monitor speakers are you trying to plug into the unit?

DO NOT parallel more than two 8 ohm speakers on either output and you will be OK. You could also use one speaker on each output. That would be easier on the equipment as it would be an 8 ohm load on each instead of a 4 ohm load on one of the internal amps. If you want to drive stage minitors, then you existing setup is fine and you will connect the monitors to the second speaker output and set the Mon switch as MAIN/MON.

Well... you probably won't like this, but here is some info: In bridged mode, a different Speakon to speaker cable is required from only the B... it is wired differently and you can only use one of the plugs. The speaker or speaker system CANNOT be less than 8 ohms in bridged mode... this precludes using speakers in parallel or multiple speakers that are less than 16 ohm impedance... such speakers are NOT commonly available as most are either 4 or 8 ohm. There is a slide switch for bridged mode on the face of the mixer. Next thing you won't like... The 1200 Watts specification is PEAK power, NOT RMS... You can get 400 watts RMS per side USING 4 ohm speakers. If you use 8 ohm speakers, each of those will get 200 watts. I use this mixer myself and ALSO repair them. The voltage swing at the outputs is about +/-60 volts MAX (peak). This is about 40 volts RMS by the time the circuit LOSSES are taken into account. Across a 4 ohm speaker you get 10 amps times the 40 volts or 400 watts. Across an 8 ohm you get 5 amps or 200 watts. The voltage rails in the switching amp are +/-70 volts DC so these are reasonable values. Bridged mode just uses both sides of the amp driven in opposite directions for higher voltage out BUT you have to use no less than a single 8 ohm speaker so there is NO advantage to bridged mode power wise. IF YOU NEED more power, use extra speakers from an additonal amp driven by the 1/4 TRS mains output jacks OR use additonal POWERED speakers driven from the same jacks. Please read my tip about the hazard regarding the SLEEVE of the cahnnel A cable when using Speakon to 1/4 plug cables being the HOT and the tip being the cold for channel A. Ground the sleeve accidentally and goodbye channel A amp...

Insufficient information ! Were you using a special cable used for bridged mode or used regular cables and just changed the slide switch to bridged mode? IF you had regular cables for A/B and just had the switch to the bridged mode NO DAMAGE WOULD RESULT. The bridged mode switch really only sets both amps to be driven from the same mixing buss as monaural. If you had a bridged cable and a plain one you would have overloaded one side amp. The amps have an "electronic" over current fuse and if you trip it you have to leave the power off for a minute or so and then re-power the amp. There is a HAZARD that I have written a tip in Fixya about PMP mixers. The sleeve of a 1/4 inch plug connected to side A is the HOT signal out of the amp as opposed to the B channel being the tip of the 1/4 inch plug...this assumes you might be using Speakon to 1/4 inch speaker cables. DO NOT under any circumstances use Speakon to 1/4 inch adapter cables as the barrel of the adapter female part on channel A is HOT to ground and you will pop the A amp.!!!! I am afraid that if you were using regular cables taht another failure occurred not related to the setting to bridged mode. The speaker leads for bridged mode are configured by the way the special bridged mode Speakon cable is wired... The slide switch only configures where the amps get there audio be it stereo busses or singly from one side. If after being off for a few minutes the amp still is totally dead, check the main power fuse which is alongside the power input connection in a plastic boat you pull out. IF THE FUSE IS BLOWN do NOT replace it as it will likely cause additional damage. Have unit repaired. There is a weak spot in these that results in arcing between layers of a multi-layer circuit board.

Bridge mode you use chan B (left connector on the back) using a SPECIALLY wired Speakon. The impedance of a speaker connected as such CANNOT be LESS than 8 ohms.

In the Main/Mon mode, the two amplifiers are separated in function. The monitor knobs for EACH channel input control the mix sent to Channel A which is for the monitor speakers. The Mon1 controls the level sent to Output A for the monitor speakers. Mon2 fader is NOT used.

The individual channel faders control the main mix and the Main fader controls the level sent to Output B which goes to the main speakers.

Yes, in bridge mode you will wire ONE Speakon that will have the two speaker wires connected to pins "1+" and "2+". You do NOT need the manual to do this, the info is right on the back of the PMP6000 itself. You will plug that Speakon into channel "B".

PLEASE note that you CANNOT go below 8 ohm speaker impedance. If your speakers are 4 ohm you MUST connect two in SERIES which requires special cables and the speakers MUST be identical. You can connect TWO 16 ohm speakers in parallel by daisy chaining, however 16 ohm speakers are NOT very common. With 8 ohm speakers you can connect EXACTLY one in bridged mode UNLESS you connect four of them in series-parallel which requires special cables and great care. Believe me you do NOT want to have an accident with this amp as repairing is extensive.

Lastly, put the speaker configuration switch down to the bridged mode.

This is how bridged mode works: Sliding the switch down basically configures the two power amps in monaural and one amp is inverted so there outputs are out of phase by 180 degrees effectively doubling the voltage.

Remember that BOTH wires in bridged mode are HOT and grounding one while amp is on will likely blow out one side or more.

Assuming that you have checked the speaker leads for broken connections and that you know the speakers themselves work okay (test with a different amp) and that you can hear sound on the headphone socket

1. Check that you actually have the power amp switch in the right position for the outputs (monitor jacks or main neutrik/speakon sockets) that you are using (see page 25 of the manual)
2. That your speakers are connected to the speaker outlets on the rear panel and not the 'main outputs' on the front panel, which are for use with a separate power amplifier
3. Check the mute button is not in
4. You have turned both the master volume controls up.

If none of the above solves the problem it is likely that the overload protection fuses on the amplifier output stage have blown and need replacing - take to a repairer
You can find the user's manual here
http://www2.yamaha.co.jp/manual/pdf/pa/english/mixers/emx512sc_en_om_d0.pdf

You require a special cable with the Speakon copnnector wired a special way. Refer to your user manual for the correct pin connections to use bridged mode and then put the slide switch in the position closest to the effects display.

Refer to figure 4.6 on page 10 and figure 4.7 showing the connection for bridge mode.

NOTE: you cannot go below 8 ohm speaker on the bridge mode... that USUALLY means a singl speaker of 8 ohms... you CANNOT parallel two 8 ohm speakers.

The single speaker cable will plug into the "B" output connector. Remember bothe the barrel and the tip of the connector if using 1/4 inch plugs is HOT and grounding either inadvertently will fry the amp.

It is NOT clear what configuration you have set up and what you consider the MONO output is, whether it is the power amp MONO side output or the line level MONO 1/4 inch jack on the top of the unit (this jack is NOT speaker output). If you can run normal stereo speakers using both sides of the power amp in the AB mode, the problems you are having is pilot error.

REMEMBER the main out 1/4 inch jacks are BALANCED TRS jacks... DO NOT put mono plugs into these.

A WARNING: If you use Speakon to 1/4 inch speaker cables, remember that the BARREL of side A is HOT, not the tip!!! You can fry the amp if you inadvertently ground that barrel someplace. (Side B has the barrel grounded) This information is NOT readily available in the manual and results in many a blown amp. They do this to implement the "Bridged" mode easily.

I have schematics and can unravel most any problem you are having.

Better way... Connect the main speakers via the Speakons and then put a Power Subwoofer to one of the Monitor connections IF you are not using both stage monitors. If you need to kill the lows to the mains, use the EQ in the PMP-3000.

Use the EQ that is USUALLY on the subwoofer to kill the highs to the sub.

Lot less cables and hardware.

REMEMBER for equipment safety, power ALL interconnected equipment from the same source be it a receptacle or power distribution system.

Powering parts of a system from receptacles strewn around a room is asking for trouble of ground loops and ground faults.