Samsung LN40B610 flickering and dying

[tertiumsquid]

Picked this TV up as a freebie today. The backlight is flickering quite badly immediately after powering on, and eventually dies completely after a minute or two. First thought is the obvious - caps.

Stuck my scope on the two biggest caps in the TV (82uf 450v), and I'm getting around 150v of ripple on them! DC voltage is measuring around 389v across those caps, which are paralleled. I soldered a 120uf 450v cap across one of them, and it didn't help the flickering at all.

Suggestions? Not hard to replace all the caps, but I'd have to order and wait for good caps or install the cheap general purpose caps available in local stores. I've also seen some threads on similar Samsung TV's involving shorting an optoisolator and changing resistor values or something, but I can't find that again.

Power supply board is BN44-00264A rev 1.4, btw.

[budm]

Re: Samsung LN40B610 flickering and dying

We will need good clear pictures of the whole backside of the TV showing all the boards, and the straight shot pictures of the whole top and bottom side of the power supply board so we can read the printed texts on the board.
It is hard to do long distant troubleshooting without seeing what we are dealing with.

[nomoresonys]

Re: Samsung LN40B610 flickering and dying

Could be a panel issue, try lightly tapping or squeezing the bezel along the top and sides, look closely for any changes.

[tertiumsquid]

Re: Samsung LN40B610 flickering and dying

Here's the pictures. I'll pull the board out tomorrow or sometime to get the bottom pic, but it's the same power supply as this one:

http://www.shopjimmy.com/samsung-bn4...t-inverter.htm

Don't think it's a panel issue, as the backlight is actually what's flickering/flashing - I can see the backlight from the back of the TV, and it's definitely what is flashing. Tapping/squeezing didn't do anything, fyi.

[dick_barton]

Re: Samsung LN40B610 flickering and dying

When the backlights are flashing, is the screen uniformly lit or are one or more of the tubes not coming on or may be dimmer than the others. Video the screen with your camera and then play back slowly.
Have you measured the resistances of each of the 4 transformers and do they match exactly.

[Andrew F. Ali]

Re: Samsung LN40B610 flickering and dying

Indeed. I think, from what I've read, you seem to have a CCFL or Inverter problem. I will not recommend you tap the Bezel at all as this could crack your screen as you may hit a little too hard or just enough to cause damage.

[nomoresonys]

Re: Samsung LN40B610 flickering and dying

Indeed. I think, from what I've read, you seem to have a CCFL or Inverter problem. I will not recommend you tap the Bezel at all as this could crack your screen as you may hit a little too hard or just enough to cause damage.

What part of "lightly" tripped you up andrew??? it's a sammy ln, I've tapped about 100 or so, haven't broke one yet.

[Andrew F. Ali]

Re: Samsung LN40B610 flickering and dying

'Lightly tap' is a relative term. Your 'light' might be 'heavy' for me. You might have more muscle power in your arm than me. Anyway my comment didn't intend to discredit you in any way. Do not take it personal. Take a chill pill, Bill........

[nomoresonys]

Re: Samsung LN40B610 flickering and dying

Take your own advice, take your 420 break mon....

[nomoresonys]

Re: Samsung LN40B610 flickering and dying

I DO NOT recommend this but even this whack DID NOT break the screen. https://www.youtube.com/watch?v=T-y5pt06HJ4

[tertiumsquid]

Re: Samsung LN40B610 flickering and dying

Alright guys, keep it civil.


Screen is definitely flashing uniformly. Backlight looks pretty stable for a couple seconds, then starts flickering (and you can hear the inverter struggling), and within 30 seconds from power on the backlight goes completely dead. It's possible to turn the TV off and back on and start that all over again.

I measured the transformers, they range from 1.52k to 1.58k, which is well within 5% tolerance (little under 2%).

Looking around at the "repair kits" for this TV, some of them have a couple capacitors for CM852/853/876/881 which are 1000uf 25v or 10v caps, some of them have a few surface mount chips and the bigger transistors in here. I decided to swap the 4 caps with what I have here (Rubycon YXA, definitely NOT low ESR, but ok for a test), and they made no difference. They're the biggest caps on the board apart from the 82uf 450v ones.

That's it for tonight as the girlfriend is dragging me out for dinner (free food yay!).

[budm]

Re: Samsung LN40B610 flickering and dying

1) Did you use the scope probe GND lead to the chassis when you see 150V Ripple? It sounds like that is what you did. You are measuring in the hot side of the circuit so for you to use the scope safely you must plug your TV into full isolation transformer for you to be able to use the scope which is then you will be able to use the negative leg of the main filter cap as the GND ref for your scope.
You can short the Opto PC803S Emitter and Collector pins together to bypass the PFC Under Voltage protection just to see if that is the cause of the flickering backlights. Make sure that you locate the correct Opto as shown in the circuit.
You should leave the DC Meter connected between the two legs of the main filter cap to see if the Voltage drift down below 360VDC or not when the lamps flicker.
Schematic: https://www.badcaps.net/forum/showpo...7&postcount=12

[tertiumsquid]

Re: Samsung LN40B610 flickering and dying

Dammit, I shoulda known that! Yeah, the probe ground was on the chassis. Used my second probe on the negative lead and the signals are basically identical.

I'll try shorting the PC803S later, but for now I watched the voltage, and at no point did it go below 389v, mostly sitting at 390v even when the backlight went off completely.

[tertiumsquid]

Re: Samsung LN40B610 flickering and dying

Tried shorting PC803S just now, no change. Monitored voltage while doing that and they were steady at 390v.

[dick_barton]

Re: Samsung LN40B610 flickering and dying

Keep an eye on the following thread with a similar problem.

[maxvalutech]

For what its worth I have a Vivo with Samsung screen and inverter and flickering display no display. The problem was solved by building up the inverter solder contact points on the several inserts on screen side.