Samsung UN50KU6300F constant reboot, bad backlights?

[nomoresonys]

Shit, my bad, that one is for surface mount, let me grab the thru hole one, here: https://www.digikey.com/en/resources...tor-color-code

[nomoresonys]

Here's one resistor chart, pretty easy to use, check some other resistors to see if you get a correct reading, wondering if your meter battery is ok: https://kiloohm.info/smd4-resistor/1004

[nomoresonys]

I tested the SK34 diode on the bottom and it appears to be bad. It checks .298 both directions with one meter and 4.8 both directions with my other meter.

I have a spare board with a similar size but it's an SK510C. Could I safely use this in place of the SK34?

I assume that was in circuit, if so unsolder it and test it again, seems bad.

[nomoresonys]

Grab the data sheets of both and compare them.

[x_orange90_x]

I tested the SK34 diode on the bottom and it appears to be bad. It checks .298 both directions with one meter and 4.8 both directions with my other meter.

I have a spare board with a similar size but it's an SK510C. Could I safely use this in place of the SK34?

[x_orange90_x]

Well lets make sure on that resistor, is it visible on here, if not what are the colors on it?

Attached is a photo of it. I don't really understand how to interpret the readings from either of my meters as far as resistance goes. I don't get a clear "600 M ohm" or even .600. I get whole numbers with decimals and they'll move around between 20 and 200 ranges

[nomoresonys]

Well lets make sure on that resistor, is it visible on here, if not what are the colors on it?

[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.

[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.

[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]

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]

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?

[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]

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.

[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.

[nomoresonys]

Are those voltages still fluctuating?

[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]

The video didn't work for me.

[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.

[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?