Q903 (SCR) fires 1/2 of a second after bright pic appears forcing SMPS
to trip shutdown mode. Leave it running with low brightness scenes no
problems. Red LED (SMPS protection) dimly lit and changes in
intensity while normally running (Red LED should be unlit). So know
this two problems is related but what is the question.

This info I need part of schematics for power supply and horizontal
section. So I can track down which is triggering SCR forcing SMPS to
shut down on brights. Chassis is functioning normally, voltages are
stable, fixed at 115V B+ via the SE115 IC.

BTW, this is AP52 chassis. I have other schematic for 50FX20B and it
is not quite similar.

HISTORY: had to replace STRM-6511 IC to get SMPS running. Chassis
already had caps replaced in many key areas.

Cheers, Wizard