No sound coming out of speakers but lights moving on board

The internal board is gone. You need to get it replaced, although may be cheaper to buy new PA Speakers.

AC hum comes from poor grounding of components.

Suspected Faulty PC board Dead Capacitor Or Mod Pot I would suggest returning it for an exchange the problem is your speaker will work on a regular stereo because a stereo powers the sound internally causing the magnets in the speaker to vibrate Headphone jacks are designed to pick up off a seperate circuit board with a different connection to the main board hence the no sound from the speaker.

The bad news is it could be any of them. or it could be the lighting- CFL's and regular flourescent lighting are bad for audio, as are switching supplies used in TV's, microwave ovens and some musical gear. They are worse than lighting dimmers for noise.

The thing to do is start at the speaker itself and work through the chain of devices to find the one distorting. An old transistor radio is useful here. Most actually do have enough power to faintly drive a large speaker- listen for scraping and rattling- it would mean the voice coil windings may have come loose or the coil form is damaged from heat.

Move back to the amp input and try again- this time listen for a clipped sound if the speaker checked out okay. It would sound like the Charlie Brown adults in the cartoons. That would be a failure of an active component in the amp. If you now hear rattling or scraping- the speaker voice coil is bad and should be repaired or replaced.

If it sounds good, move back to each deck. apply your radio- volume turned down to an input it one is provided. Each should sound clean like the amp did. If no sound or distorted sound is found here- which is the most probable location, it is likely one of the IC chips is at fault. Likely a 4558 if an IC fault, otherwise suspect dirt or hair on the encoder connected to the spin platters.

Zombie post, I know... But, I have a solution for this. Remove the power amp unit from the rear of the sub cabinet. Remove the sheetmetal shield, noting the 4 allen screws on the side. Th daughterboard that the 4 screws thread into is a filter for the power amp's output, and is the last circuit that the powered signal goes through before hitting the speaker. If you inspect the solder joints, you will likely find that there are several which are bad. they will look cracked, potentially discolored in the crack. Resolder the joints, making sure to use good solder, and fill the joint. The most likely culprits are the 4 joints belonging to the 2 blade connectors which attach the daughter board to the larger board (which is the actual amplifier component).
Again, sorry for digging this problem up from the grave, but when I searched for a solution earlier, this was one of the only posts that resembled my issues, and it never got a good solution.

Just had the baby brother (ACX450) with this problem...opened the amp... screws from sides and or top (including 2 hidden under handle covers).

The power cable from the power transformer had come off the connector on the circuit board in spite of goo they had put on it. Put connector back on and secured the cable and works perfect,

Since your display lights, yours is likely a different problem. I have also seen similar ones that the cable to the speaker had been pulled off its connection on the circuit board, rendering no sound. See if you have sound at headphone jack. and if none, how about the preamp output jack? Note you will only hear the left side using earphones as these jacks are monaural.

Not a fuse. First thing, to check your speaker (amp unplugged, of course), touch the + and - speaker connections to a 9V battery. If you don't hear a pop sound then your speaker is blown. Thus, no output sound. If speaker is OK, then the output IC is your problem.

You don't specify which model Phonic mixer in question.
Is it a powered mixer ? And are you plugging your speakers into the speaker outputs ? If it's not a powered mixer and you're plugging speakers into the Line Outputs, you're not using a power amplifier between the line outputs and your speakers - this won't work.
If it is a powered mixer and you are plugging speakers into the speaker output connectors and still getting little or no sound, check your speaker cables and the speakers themselves by plugging them into known good amps.

When it was knocked over it may have cracked the main circuit board, but does the pilot light come on at all? If the pilot light comes on but no sound is output from the speaker try plugging some headphones into the head phone jack and then turn it on and see if you can hear sound in the headphones. I have had a similar problem before and the main speaker had gone bad but it would still play thru the head phone jack.

clavinova 83s...comes on but goes off within 20 sec.,sometimes comes on display lights up but no sound or functions?