DC power failure
These faults normally lead to an overall failure of the d.c. power distribution system apart from Standby and possibly audio power. Failure in one section of power generation would inevitably lead to the other parts turn- ing off as the protection circuit kicks in. The task is to find the part of the power distribution system that is the initial cause of the failure. The following is a suggested series of tests for plasma screens:
● Is the set in Standby?,
● Check d.c. outputs,
● Check the d.c. voltage (around 400 V) from Flyback switching transistor,
● Observe the d.c. build-up of the various d.c. power generators (PFC, Flyback converter and resonant converter) as well as their control signals in turn immediately after switch on from cold. The manner in which the d.c. outputs and the PWM signals are built up would give a good indication as the location of the fault. PWM control signals and d.c. outputs should be present for a very short time before the set trips and goes into standby.