LED LCD TV SMPS thermo fault

I have a Kogan 42" LED LCD TV that loses back-light after about 50 minutes running time. After cooling down it works fine again.

It has the PSU board bsf-pi420401a.

It can't produce the fault with the back detached, to even find out which voltage is going down.

Has any one had a similar problem with this board, and maybe found the fault? I noticed that it is widely sold as a spare (but not in Australia :( ).

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Thanks

Tony

Reply to
Tony
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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.

Reply to
Sjouke Burry

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...

John :-#)#

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Reply to
John Robertson

Thanks, I was actually thinking the same. However, why has it been running OK for 2.5 years? Something most have happened. I'd hate to see the PSU going up in smoke one day.

Tony

Reply to
Tony

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.

Tony

Reply to
Tony

hear, hear! Hair dryer and cold spray are your friends when it comes to these pesky intermittent problems.

for a really 'available' cheap esr, take a look at Bob Masts's LCR meter using soundcard:, I think circa June 20th he released his 'new' LCR meter aimed at these esr measurements.

Bob Masta

DAQARTA v7.50 Data AcQuisition And Real-Time Analysis

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Scope, Spectrum, Spectrogram, Sound Level Meter Frequency Counter, Pitch Track, Pitch-to-MIDI FREE Signal Generator, DaqMusiq generator Science with your sound card!

Reply to
RobertMacy

The solution is to go to Youtube and look up Renee Everhart and watch one of her videos. By the time she starts getting naked and playing with her snatch, you will want the back light to go out.

Reply to
Phoena J.

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.
Reply to
Sjouke Burry

Phoena J. wrote

Hey NSA, could you track down this guy, and terminate his internet access?

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beslutning at undlade det.
Reply to
Leif Neland

I don't know the exact model you have, but my 42" Kogan LED/LCD has a Samsung screen so I'd expect the LEDs to outlast the cheap Chinese build of the rest.

BTW, mine periodically faults to a "digital raster" in either the full screen or some lesser rectangular area. It also periodically locks up and has to be power cycled on the frame.

Reply to
pedro

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?

Tony

Reply to
Tony

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