Left speaker not working, system crackles if left side is active, alright when left side shut down.

buy a canister cold spray and spray on some active components if the noise begins You have a thermical failure in a component on the board can be faltering resistorcircuits or resoldering some active components.

If it come back on after shutting down, you have a part overheatinga and then working again after it's cooled off, rather than "blown. You will need to take it in for service.

Have you tried isolating the problem, like switching cables from the left side that is not making noise? Also check connections,
I say this all the time and use all the time.... electronics spray contact cleaner, usually takes care of crackling noises
really hope this helps?

I had same issue with the series below (525). I removed the amp and there was an aluminum inside cover I took off the amp that was secured by a single top and single bolt/nut combo. This was holding in all the heat but also perhaps to physically dampen potential vibration of some of the components. I got mine to cool down 10c less than one with the manufacturer's case left intact (unaffected speaker) and it quit cutting out on me without having to devise a complex fan. Hopefully this is true for the PRX 600 series as well.

Most likely bad electrolitic capacitors from it sitting for a long time

in your system preferences click on sound and adjust the settings you need.

"Tested with other speaker and cable" ... you did not tell us the results of the test. If swapping the speakers and cablles still had the same dead side, it is probably the power amp for that side and not the mixer part. Take in for repair. If you had an accident of speaker cable not being plugged in fully or pulled out while operating, this pops the power amp real quick. They also just plain fail at times. Plug a set of headphones into the MONO out jack. If you can hear audio going through the unit then the mixer is OK... and the power amp on the failing side has a failure. Note the headphones will be low level and probably only one side, usually the left as this is a mono signal and headphones are normally stereo.

It could be that the input jack is or cable is damaged. The input to the right speaker is from the left speaker via speaker cable. Check that wire and try a new one. All speakers are susceptible to some type of interference. Make sure the cables aren't tangled and free from other powered equipment.

Hope this helps

To troubleshoot the problem start with the bit that is working - the left speaker.

1. Unplug the input leads on the back of the left speaker and swap them round.
2. If sound now comes out of right speaker and not the left the problem is with your sound source (computer, IPOD or whatever) or the connecting cable is faulty.
3. If there is still no sound from the right speaker try turning the volume control knob up and down quickly several times - does this produce any sound from the right speaker? Sometimes the electrical contacts get dirty and this can help clean them.
4. Turn the speakers off using the volume control knob. Disconnect the speaker wire for the right speaker from the OUTPUT on the left speaker (push the red and black tabs downwards and gently pull the wires out. Find a small 1.5 volt battery (an AA or AAA size will do nicely) and touch the bare ends of the speaker wire briefly on the battery terminals. If you hear a slight crackling sound the wire and the speaker are okay and the problem is in the amplifier, which will need repair or replacement - not a job for an amateur.
5. If you don't get any sound from the battery test find another piece of speaker wire (any piece of 2 core cable with bare ends will do for testing) and repeat the battery test. If you get sound then replace the speaker wire. If not remove the speaker wire again and go to next step.
6. Lay the speaker face downwards and carefully unscrew the back panel (don't do this if it is still under manufacturers warranty - take it back for repair or replacement). Lift the back panel off carefully and slowly taking care not to pull the connecting wires inside the cabinet, which will probably be quite short. You may have to settle for just rotating the back panel slightly so that you can see inside if the wires are too short to do otherwise.
7. Use sticky tape to tightly attach the bare ends of the speaker wires to the terminals of the battery. Touch the loose ends of the speaker wires on the two metal terminals where the internal wires are joined onto the back of the big loudspeaker cone. If this produces a crackling sound it is the internal wiring in the cabinet that needs re-soldering. Otherwise the loudspeaker unit has failed and will need replacement.

Probably NOT a transformer. Most likely in the power amp. Many have a thermal cutout that shuts the thing down when the chip/stick gets to hot. Your description leaves some questions... IF you don't get anything at all out of the left, then look first for a short from the amp to the output jack. This probably has a dual chip amp in it and half that chip may be bad heating up and shutting the whole thing down.