Kicker kx1200.1 amps (2) cut out under load

[jimmyjames22]

I Have (2) kx1200.1, green pcb, 2002 production, and both amps have the same problem. They both jump into protect when slight load applied at 4ohm. after a few seconds it comes out of protect and plays for a second then repeats over and over. rail voltage will drop from 77vdc to 56 at which the amp will enter protect and open speaker relay. Anyone have this problem? or an idea what is wrong?

[Perry Babin]

How low is the voltage dropping at the power/ground terminals?

Place the black meter probe on the ground terminal of the amp (not on the point where the ground wire connected to the vehicle).

[jimmyjames22]

battery voltage stays steady at 13.8 vdc from positive and negative terminals while amp enters and exits protect mode

[amptech]

you can check service car amplifiers via computer psu's/bench power supply's...

I would apply signal to the amps in put now with out a load connected to the speaker end and place your meter on ac volts range and in turn adjust each level pot to test each channel and record the voltage's... never cross the power in put ground with the speaker ground connection... now power down and connect speaker loads and reapply the same test if it cut's out as you turn it up power of and replace the o/p transistors and check components within the power stage for shorts or open circuit readings..

possible faults are o/p transistors that have been stressed, broken level controls, power supply switching fet's and the pwm chip..check the large diode within the dc in put circuit.

[amptech]

Carry out current tests with speaker load and then with speaker loads...

[amptech]

was meant to say with out loads then with speaker loads...

[Perry Babin]

Does the rail voltage drop if you have no speakers connected to the amp?

If you have speakers connected but no RCAs plugged into the amp, does the amp go into protect?

With no speakers or RCAs plugged into the amp, dies the amp cycle into protect?

[jimmyjames22]

Thanks guys! I hope to find time to tomorrow to check out those leads. Day job keeps me from the repair work some days Thanks again. James

[jimmyjames22]

Hello guys the amp will not go into protect until it is put to work with an input signal and speaker being drivin. I replaced 8 Irf3205's on one of the amps . even though they tested ok I had them to try and it didn't make any difference. any ideas?