Cause:heating. Solution:cooling,moving air. Try aiming a blower at the back of the tv, and see if if stays on. If that works, get a 6-8inch computer van and screw it into the right spot. Those tv's/monitors have a rotten heat management.
A hair dryer and some cold spray will help you find the culprit, although in most cases it is a bad capacitor - look for ones with bulging tops or where the insulation sleeve has pulled down relative to others of the same brand.
An ESR meter can help with this if you read up on using it...
(Please post followups or tech inquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
Thanks John. I have used the heat blower, trying to get the fault to show, but maybe not long enough. I was already worried that the fault may be in the LEDs, but that'd be a slim chance. I heated up the 2 other boards as well, no change. No caps bulging and no dark spots on the pcb.
The specs for power transistors at full load and temp was
4 years in the past. Reason:the layers started to diffuse into one another at high temperature, turning NPN into N?P?N?. I doubt if the newer ones will last 4 years. At half load/temp, they last almost forever. And that is bad for bizznez.
Sorry to hear that. Should be rather complex to deal with the digital picture works:(
Not sure which brand screen mine has, but there is a quality problem. After cooling and heating the PSU had no results, I went a little deeper. I found the two 100uF filter caps of the PWM circuitry for the backlight to get really hot (lousy ESR) I replaced them. No change. Then I found another 470uF Elecrto cap in the supply for the PWM circuits to be totally dry, but replacing this one also was no solution. Amazing how stuff keeps working with half dead parts.
Then I started to disconnect loads while the fault was showing (the PSU is actually quite good and caters for shorts by switching off), I found the culprit was one of the four LED backlight strings. Nice short when hot enough. You can even hear the spark (@43V).
Unfortunately there are always 2 sets of LEDs in series, so if you disconnect one you are taking two out of action. To my surprise the TV works just fine on a half a set of LEDs. I'll leave it like this. Changing the LEDs would be a major operation I would only embark on, if I had a spare screen to play with.
Has anyone ever replaced the LEDs of a 42" LCD screen?