Kicker KX650.4 little to no ouput

[philk]

Got a Kicker 650.4 that has very little output. I checked the signal coming out of the preamp board with my scope. It looked fine, but by the time the signal reaches the output transistors, it's not much of anything. I assume something is wrong between those two points, but I don't really know where to look. Anyone know of a common failure or where to go from here? I could easily follow the signal if I had a schematic, but those seem hard to come by for car amps.

[Perry Babin]

Find the muting transistors. They should have their emitter connected to the secondary ground. Their collector will be connected to the bases of the transistors in the differential amplifier (possibly via low value resistors). The circuit should be similar to the following diagram. The KTC1303 in the diagram is what you're looking for. It won't be a KTC1303 but it should be an NPN transistor.

http://www.bcae1.com/temp/cheapampaudioschematic01.swf

With the black probe on the emitter of the muting transistor and the red probe on the base of the muting transistor, what's the DC voltage?