Samsung UN40H5203 Flashing Backlight

[jason123]

Happy holidays folks.

I just got this Samsung with weird symptom. Powers up and the backlight flashes very bright at roughly 1 Hz. When I first got it, it flashed few times then stopped. When I opened up the panel, the majority of the LEDs where dead. I replaced them all put it back together and it's flashing again. I don't want to troubleshoot while flashing because the LEDs are ultra bright and will eventually die.

Seems that the LED drive circuit doesn't have sufficient current limit?

It's BN44-00769C power board. Has anyone seen this before? The backlight voltage at pin with LEDs disconnected is roughly 200 V and doesn't fluctuate with the LEDs disconnected.

[budm]

Re: Samsung UN40H5203 Flashing Backlight

1) You indicated that the old LED's were dead, were they shorted out or open circuit?
2) What LED's did you use for the replacement, spec?
3) lift up one leg of the diode d9801? (next to blue disc cap C9842) in the LED driver section then check the resistance between the two legs of that diode in both directions, report the result.
4) The LED's are connected in series and the LED power supply rating (printed on the board) is 151.8V @425mA with load, so 200V without load is correct.
5) Provide the P/N of the LED driver SMD IC9805 on the bottom side of the board by the LED connector.

[jason123]

Re: Samsung UN40H5203 Flashing Backlight

Hi budm
1) You indicated that the old LED's were dead, were they shorted out or open circuit?
Recall upon first few power ups, these were flashing, then eventually stopped. 2 strips had many shorted. the 3rd strip has several open.

2) What LED's did you use for the replacement, spec?
I use the 1W 3V LEDs (I've used them before on Samsung, very similar to the ones that were on the board, physically)

3) lift up one leg of the diode d9801? (next to blue disc cap C9842) in the LED driver section then check the resistance between the two legs of that diode in both directions, report the result.
One direction shows open (High Impdeance) and the other direction 4.62 MOhm

4) The LED's are connected in series and the LED power supply rating (printed on the board) is 151.8V @425mA with load, so 200V without load is correct.

5) Provide the P/N of the LED driver SMD IC9805 on the bottom side of the board by the LED connector.
Marking on the IC is 7014X

Thanks

[jason123]

Re: Samsung UN40H5203 Flashing Backlight

Anything else you can suggest looking into?

[vinceroger69]

Re: Samsung UN40H5203 Flashing Backlight

maybe same as in this video disconnect pwm wire if your set is the same
https://www.youtube.com/watch?v=sQn5QZ4SK80

[jason123]

Re: Samsung UN40H5203 Flashing Backlight

Thanks. This TV is responsive to power button and the backlight flashes even if the main board is disconnected. I think it's LED strips or Power Supply. Maybe I used the 3V LEDs and I should have used the 6V instead?

[vinceroger69]

Re: Samsung UN40H5203 Flashing Backlight

do samsung even use 6v leds i know lg do though whats the lcd panel number used in this set maybe then we can find the led specs

[jason123]

Re: Samsung UN40H5203 Flashing Backlight

Here is the label on the panel.. not sure if it tells you the LED spec?

[budm]

Re: Samsung UN40H5203 Flashing Backlight

Were these your LED strips with 38 LED's total?
http://www.silvershoptvparts.com/sam...r-un40h5203af/

[jason123]

Re: Samsung UN40H5203 Flashing Backlight

That's it eaxactly.. 12 leds center 13 top and 13 bottom.

[jason123]

Re: Samsung UN40H5203 Flashing Backlight

You think its the LEDs that are causing the problem? All have been replaced and all light up. Would love to get this repaird asap. I ordered a ps board.. waste of money?

[vinceroger69]

Re: Samsung UN40H5203 Flashing Backlight

3v leds would use 114v 6v leds 228v your power pcb states 151.8 v i hate issues with backlights i usually just replace the lot like you have and that fixes the issue maybe budm will have more ideas on what too check next

[jason123]

Re: Samsung UN40H5203 Flashing Backlight

A new power supply board just arrived and it's doing exactly the same.. flashing backlight at 1 Hz or so... it's got to be the strings

[budm]

Re: Samsung UN40H5203 Flashing Backlight

Sounds like you have to get the LED strips out and wire them up out side the panel and hook up to the power supply board and see what is going on.

[jason123]

Re: Samsung UN40H5203 Flashing Backlight

Just a quick update.. got a set of backlights from China ($38.00 + a couple of weeks) and it fired right up. All is good.. thank you

[nomoresonys]

Re: Samsung UN40H5203 Flashing Backlight

So the first set of backlights you replaced were bad, were they new, if so could you share where you got them? wouldn't want to buy from them if they sell bad lights.

[jason123]

Re: Samsung UN40H5203 Flashing Backlight

No, the first set I installed where the original but with LEDs replaced.. They worked great outside the set with a tester.. so I'm not sure what was wrong with them.

[nomoresonys]

Re: Samsung UN40H5203 Flashing Backlight

Ok, I see, thanks, nice fix.

[budm]

Re: Samsung UN40H5203 Flashing Backlight

May be you should try out the old set of LED powered by your power supply/LED driver board so you can see what is going on.
LED tester only puts out 30mA so any bad connection, weak LED may not show problem until they driven by high current.

[jason123]

Re: Samsung UN40H5203 Flashing Backlight

So my first step was to replace LEDS. Once i did, i tested with original power supply. They turned on blinking very bright. Got a new ps board. It did the same thing but i left the strings connected too ling while i was attempting to take measurements... eventually most leds shorted opened again...unfortunately unsalvageable at this point .. none related quick opinion.. up for sale for $20 is a samsung 50" 4k tv... any guess if this issue is fixable (color line and color bleeding on top)