Faulty CCF tube
For LCD panels, a fault in one CCF tube (if more than one is used), would normally result in the inverter being turned off by the micro-controller either immediately or after a short delay. With one tube malfunctioning, the brightness will still be distributed evenly and the picture will look normal with almost un-noticeable low brightness. However, once one tube goes down, an error signal is sent to the micro-controller and the inverters will be turned off and the set would probably go into standby. Check the over-voltage protection/error signal. Check the PWM tube brightness control waveform; if present, then the fault is in the oscillator.
The classic stuck in standby fault (plasma and LCD)
Invariably, a fault in one section such as the power supply, micro-controller and even video and formatting section leads to the set going into standby as a result of the extensive feedback protection system employed in PDP sets. Once into standby with all other power turned off and all processing and control halted, it is difficult to find the original cause of the fault. However, tests during the start-up sequence in the period between switch on and the set going into standby may provide important clues as to the location of the fault. The precise start-up process differs from one set to another, but they all follow a general sequence which has been summarised above.