HLN507W 50" TV stays on only 3-5min

[dewtan]

History: Lamp replaced twice in last 7 yrs. Color wheel replaced 2yrs ago (screeching). Logic Board replaced 1. 5 yrs ago. all parts got from DM. TV has been good as new for the last yr and half.
a month ago started having trouble powering up. Then would power up and stay on for 3- 5 min and lose picture then sound. Lamp 2yrs old so replaced lamp. No help When TV shuts down, Both fans continue to run and the three leds remain lit on the Logic bd. No lites on front of TV lite. unless use try the pwr button on remote, then the top standby lite blinks. but nothing changes. Plug must be unpluged to shut TV down. When on for the 3-5 min Picture and sound is excellent. Replaced the lite ballast. no help. Checked input to the Ballast 385 VDC, Normal when shutting down losing the 5v turn on voltage to the Ballast. Could this be logic board went bad again? Am technical 46yrs with electronics.

[dewtan]

Dewtan again: Actually tv will stay on with good picture and sound for 10-15 minutes if been unplugged for extended time. was able to reset lamp. During this 15 min. i can turn on and off with remote, acts normal, except the three lites on front. labeled timer(top), lamp(middle, Temp(bottom).
As per Manual the lamp lite is to be lit during normal operation with TV on. Now when operating normal NO lites are lit. I have noted the DMD board is what supplies the 5V logic to the lamp ballast to lamp on. still looking for any expertise.