Samsung UN50KU6300F constant reboot, bad backlights?

[vinceroger69]

If I connect the spare power supply to the main and leave the backlight disconnected, should the tv boot up? I would expect it would, just as if backlights were shorted.

not sure as the tv maybe detecting a fault with backlights disconnected, there was a thread the otherday where the op was having no backlight isssue turned out it was a bad solder joint so check the psu for cracked joints etc

[x_orange90_x]

not sure as the tv maybe detecting a fault with backlights disconnected, there was a thread the otherday where the op was having no backlight isssue turned out it was a bad solder joint so check the psu for cracked joints etc

I'm going to give it a try. At the very least I should get a different blink pattern on the standby light.

[x_orange90_x]

not sure as the tv maybe detecting a fault with backlights disconnected, there was a thread the otherday where the op was having no backlight isssue turned out it was a bad solder joint so check the psu for cracked joints etc

I tried with the spare power supply and the tv boots up. I can see an image with a flash light. So that confirms the power supply is at fault. What should I be looking for on it? Nothing appears to be burnt, leaking, or swollen.

I did a quick voltage check on the plug to the main board and I have 5v standby. The other ones such as 13v and PS_ON fluctuate all over the place.

[nomoresonys]

Did you check all the diodes on top of the board.

[x_orange90_x]

Did you check all the diodes on top of the board.

I actually was just searching the forums with the board model number BN44-00807A and someone said to check two diodes because one of theirs was shorted. I will remove and test those two tonight.

https://www.badcaps.net/forum/troubl...78#post1751678

I seen in another post there's also a diode on the bottom that fails on some people:

https://www.badcaps.net/forum/troubl...-fix#post80203

[x_orange90_x]

I removed one leg of each of those two diodes from the board and checked them. D9002C checks good, but D9001C reads .298 both directions.

[nomoresonys]

Yep, that's a bad one, maybe switch m both out for good measure.

[x_orange90_x]

Yep, that's a bad one, maybe switch m both out for good measure.

How important are these diodes? Do I need to replace them with the exact same values or could I harvest one from a scrap board?

[x_orange90_x]

I replaced it but I'm getting the same symptoms. I can hear a faint fast clicking like it's trying to come on. I've attached a video of the sound.

[nomoresonys]

The video didn't work for me.

[x_orange90_x]

The video didn't work for me.

See if this works:

https://drive.google.com/file/d/1FOr...w?usp=drivesdk

[nomoresonys]

Are those voltages still fluctuating?

[nomoresonys]

Quick test, try heating C9371 with a hairdryer for a minute or two and retry it while it's still hot, no joy maybe test that resistor and test that transistor on the heatsink right there by it, see if any of the 3 pins are shorted to the other 2, or reads low ohms, should be able to test those in circuit. Try tracing where that bad diode goes, what components it leads to. And as always, make sure all your solder joints are good on bottom of board.

[x_orange90_x]

Quick test, try heating C9371 with a hairdryer for a minute or two and retry it while it's still hot, no joy maybe test that resistor and test that transistor on the heatsink right there by it, see if any of the 3 pins are shorted to the other 2, or reads low ohms, should be able to test those in circuit. Try tracing where that bad diode goes, what components it leads to. And as always, make sure all your solder joints are good on bottom of board.

I was just thinking about that transistor last night. I will check it and that resistor. I did not recheck voltage on that plug, bit I imagine they're still jumping around because the board is still power cycling.

[x_orange90_x]

I have a feeling it's that transistor. I will check that, the resistor, and that capacitor tonight. Id like to have kits of components on hand so I don't have to order so often. Like variety kits of transistors, diodes, resistors. Does anyone else keep stock like that, or just order what's needed when it's needed?

[x_orange90_x]

Last night I checked out a few things. First I tried heating up that capacitor and powering on. No change. Then I checked that resistor. It's supposed to be 600Mohms, and my meter being auto ranging showed it as 1.2. I'm not sure what that means, but it's showing resistance so I assume it's good. Last I checked that transistor. I was getting funny readings from it (different measurements between base/collector as base/emitter) so I replaced it. Also NO CHANGE. I still am getting power cycling and that buzz/tick sound in the video I shared earlier.

Whatever is bad literally prevents the whole board from powering up, and instead it just "reboots" over and over.

I forgot to check DM871 on the bottom of the board. I seen Hamie's thread about it being a common failure for this model power board. Despite being surface mounted, I still have to remove this diode to check it, correct?

[nomoresonys]

Go ahead and check that diode in circuit, if it gives unexpected reading then you might need to unsolder to see, not sure what you mean by 1.2 on the resistor, they should be close to the rating of the resistor, if unsure maybe de-solder it and check.

[x_orange90_x]

Go ahead and check that diode in circuit, if it gives unexpected reading then you might need to unsolder to see, not sure what you mean by 1.2 on the resistor, they should be close to the rating of the resistor, if unsure maybe de-solder it and check.

I honestly don't know either! That's how my meter displayed it. 1.2 with the ohms symbol. I think it's probably okay though.

I will check that diode though. HOPEFULLY that is it.

[nomoresonys]

Can you narrow down the location of the buzz-tick, maybe with a straw to your ear or such, make sure ALL the solders are good on bottom of board.

[nomoresonys]

I honestly don't know either! That's how my meter displayed it. 1.2 with the ohms symbol. I think it's probably okay though.

I will check that diode though. HOPEFULLY that is it.

Well that's way off then, lift a leg of resistor and recheck.