I have a cheap chinese plasma cutter cut50d.the unit comes on and the fan runs but pull trigger no spark or air.i did a continuity check at the cable and it has continuity.plus at the switch when i pull the trigger the ohm meter moves.the red diode light is not lit.could it be a solenoid problem?

Yes.

I have a damage board Chiry SM4-01, of my Colossal Tech CUT50D the transistor that blow up is the Q3, someone that can help me to know what is this transistor? I will appreciate any information that you can provide me.!

I had the same problem... found out it was a broken wire inside the insulation on the red wire inside the torch handle. it feeds the switch that excites the air and the voltage.

You need to check the internal connections coming from the panel switch connections through to the botom PCB. My guess is that a wire or plug connection is disconnected or losse.

I doubt the solenoid is the problem. first,lets see what is working, the power fan comes on, which on the Dual voltage model is powered by 24 volts dc. This means the powersupply/ voltage regulators are working correctly,( air solenoid, and HF section are powered by same 24 volt dc source). If the fan was not working, i would have assumed it to be a faulty regulator. I believe Giant tech guy is correct, and its something as simple as a loose connection between the 2 pins where the torch plugs into, to the bottom board located in the front of the machine. If all connections are good, the only thing i could think of would be a faulty relay located in the HF Board, ( the small board located on the bottom front of the machine),its a little blue sealed relay, take the board out and inspect for poor solder joints. If that dosent show anything, put the board back in , leave cover off, turn on machine and try tapping either one of the 2 relays with a long insulated screwdriver,( while holding the plasma torch switch on), its possible the vibrations could unstick or seat a burned contact), , but be warned, If you dont know what you are doing, these machines could be lethal if your rooting around in there while its powered up. Besides high voltages and currents, MOSFETS exploding in your face can really hurt you...Hope this pointed you in the right direction....good luck