Samsung LCD Notorious "2 Seconds Black" faulty backlight

[90Ninety]

Hi All

Another project , this time another Samsung LCD Model: LE26R74BD

This has the notorious 2 seconds black fault. The LCD Panel works , this was tested in dark with Torch
Four bulging 1-MilliFarad Caps were replaced on the PSU ( Model BN9603833A) . The fault still resumed

. Originally the backlight switched on for around half a second . This was improved to 2 seconds after swapping Inverter board

I suspect either I have a faulty lamp CCFL or PSU component . Seemingly there are several compatible PSU for this TV ( BN96-03057A , BN96-03642A to name a few )

Before swapping out the PSU or checking the lamps , it would be nice to hear your thoughts , suspicions, experiences and hunches with this issue

I am fairly experienced with electronics and Meters , I just lack time to check everything at the moment

[selldoor]

Re: Samsung LCD Notorious "2 Seconds Black" faulty backlight

If you have swapped out the inverter board then I should examine the lamps.
Have you any spare lamps you could use for test - perhaps build a test bulb
see any post by Budm and in his signature there is a link on how to make one from a 14w cfl

Please can you update your profile with country and mains voltage

[90Ninety]

Re: Samsung LCD Notorious "2 Seconds Black" faulty backlight

Ok the CFL test is complete , the monitor still switches off , even with the CFL bulb attached. Every port was tested .

Some other strange things I have noticed :
When inserting Mains Voltage 240 V , there is a kind of very faint whistle sound which gets higher pitch after 3 seconds then stabilizes

Upon switching on the TV, there is a brief second of 100% brightness , then a second of 40% brightness , then back-light stops .

There is matching sounds , seemingly on when the screen dims there is a kind of slight arcing/buzzing sound which stops when backlight diminishes
Seemingly there is a component dragging the voltage down , I may be wrong , just my suspicion .





Using a flashlight , the settings menu can be accessed , all settings can be changed, apart from brightness , as soon as the brightness spectrum is changed , the user is thrown out of the menu !

I am wondering if it is worth replacing the PSU , as they sell for around £20

Again your thoughts are cherished

[wreksta]

Re: Samsung LCD Notorious "2 Seconds Black" faulty backlight

im leaning toward main av board on this one mate as you say the brightness option kicks you out of menu

[tom66]

Re: Samsung LCD Notorious "2 Seconds Black" faulty backlight

Could be a possibility - try putting TV in standby then pressing info-menu-mute-power and selecting reset option.

[90Ninety]

Re: Samsung LCD Notorious "2 Seconds Black" faulty backlight



And In the Back of the Net

'Good ol' Cowboy Heatgun trick and she is alive

Wonder how long it'll last ........................

[selldoor]

Re: Samsung LCD Notorious "2 Seconds Black" faulty backlight

A bit more explanation of what you did might help others ? and me
Like how hot how long for taped up? and so on.

[90Ninety]

Re: Samsung LCD Notorious "2 Seconds Black" faulty backlight

A bit more explanation of what you did might help others ? and me
Like how hot how long for taped up? and so on.

well After changing the capaictors, I changed the Inverter board which done nothing really

I then dusted all of the inside PCBA's using a paintbrush . I then proceeded to heat the PCBA's and components for around 2 minutes using a heat-gun , alternating between high and low heat , in a waving circulating fashion .I gave all components enough heat to make them hot to the touch . I waited a few minutes to col down , re-assembled and voila

[selldoor]

Re: Samsung LCD Notorious "2 Seconds Black" faulty backlight

Ok - well done - thanks for that - be interesting to see how long it lasts.

[comptek]

Re: Samsung LCD Notorious "2 Seconds Black" faulty backlight

i just did one of these a quick flas of the backlights and that was it.....checked all fuses and a 3.15a near the top end of the board had blown and i measured the fets and the one in line with the fuse measured wrong changed it now all ok