LED LCD TV SMPS thermo fault

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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  
:( ).

(like  
http://www.rivervalleyelectronics.net/p-22806-westinghouse-bsf-pi420401a-power-supply.aspx )

Thanks

Tony

Re: LED LCD TV SMPS thermo fault
On 09.07.14 3:48, Tony wrote:
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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.

Re: LED LCD TV SMPS thermo fault
On 9/07/2014 11:20 AM, Sjouke Burry wrote:
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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



Re: LED LCD TV SMPS thermo fault
On 09.07.14 8:11, Tony wrote:
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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.

Re: LED LCD TV SMPS thermo fault
On 07/08/2014 6:48 PM, Tony wrote:
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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 :-#)#

--  
(Please post followups or tech inquiries to the newsgroup)
John's  Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
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Re: LED LCD TV SMPS thermo fault
On 9/07/2014 1:34 PM, John Robertson wrote:
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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


Re: LED LCD TV SMPS thermo fault

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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.

Re: LED LCD TV SMPS thermo fault
On 10/07/2014 10:56 PM, pedro wrote:
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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



Re: LED LCD TV SMPS thermo fault
wrote:

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

Re: LED LCD TV SMPS thermo fault
On 07/09/2014 01:48 AM, Tony wrote:
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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.

Re: LED LCD TV SMPS thermo fault

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

--  

beslutning at undlade det.



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