LG LM556200 Power Board LED Blinks 4 times

 LG 55LM6200  Screen goes dark after a few minutes, suspect protection mode is engaged-- no sign of thermal issue. On power board there is a LED, blinks amber in 4 blink cycles. Measured voltages ok, both backlight strips appear to be good. I have the SM, there is no reference to this power board LED, beyond the fact that it is there. Does anyone know what the blink codes are for these LG power boards? Thanks!