I have been using my car amp for double 10"s without any problem for a half year but when i connected the amp for double 12"s it played for 5sec and then it turned itself off. I have looked at the circuitboard but nothing seems burned. Where should i start looking?
ok, using an volt meter check your voltages. make sure you have 12v at the power and turn on lead. Is there a power led on the amp? Is it on, it should be on. Is there a protect light? is it turned on? It should be off. If it has power and the protect light is off re install your old subs. do they still work? If they do you have a bad 12" sub. if not your amp is suspect.
Power source is ok and everything else but as soon as the turn on lead goes active all 3 40ampere fuses on the amp burns, and that is even when no subs are connected. What i dont understand is how all of that could happen just from changing subs from 10" to 12". I should also mention that the 12"s plays without problem with other amps.
your amp has a dead short.my best guess at this time is the outputs are gone ( shorted) dont know why, possibly the wires to the speakers touched together or to ground. you will need to get your amp repaired or replaced.