JL Audio HD750/1 Repair

So I have this amp on the bench.

PS working. Outputs have signal/oscillation.

Not passing signal. No activity on the status led. LED signal seems to be generated on pre-amp board so leaning toward a lack of power on preamp board. Header pins probe most voltages +/-15, +/-5, etc.

Hard to probe pre-amp board while amp is powered, but I did order jumper ribbon cables. Don't have them yet.

Ideas?
 
Have you operated all pots and switches through their entire range while listening for audio to see if it every played through (even just for an instant)?

With a speaker and signal source connected, did you operate all pots and switches in all combinations to see if any audio/static/noise ever played through?