Samsung PN42B450B1DXA Turning On and Off Repeatedly

[PirateFan06]

Good morning guys. I was recently given the tv mentioned above from a guy at work bc he was going to toss it out. When he gave it to me, the picture was off but it had sound. Once I got it home it started flickering on and off but the sound still played constantly. At that time I checked all power and the numbers matched the sticker located on the back of the tv. Now the tv will not stay on and begins to turn on and off as soon as it's plugge I. I've checked certain test points and fuses and they all look good as well. I've been unable to find any puffy capacitors or anything. I've tried to check for a short in the y buffer but I'm not exactly sure where to ground the black lead out on the board. Any help on where to start would be greatly appreciated.

[vinceroger69]

Re: Samsung PN42B450B1DXA Turning On and Off Repeatedly

Samsungs sometimes suffer from bad solder joints on the power supply if i was you i would re solder all the parts that are on the heat sinks etc even if the joints look good maybe reflow/add a little more solder.

[ReeceyBurger123]

Re: Samsung PN42B450B1DXA Turning On and Off Repeatedly

Test the Ysus/Xsus for short circuits to ground from Vs use chasis as ground.

[PirateFan06]

Re: Samsung PN42B450B1DXA Turning On and Off Repeatedly

Good morning ya'll and thank you for your quick replies. I tested the x main and y main to see if they were grounded out and everything seemed fine. I also took the main power board off and checked the back. All soldering joints looked okay, but my soldering skills are limited to car stereos. Not sure if I want to mess soldering those connections yet or not. Should all heat sinks be grounded? 1 on the power supply was and all on the y main were. Also just messing around I noticed the 5.3v connections on the power supply were grounded out. I did this while it was taken off the tv. Not sure if it's supposed to be that way, or if I'm painting myself even dumber with electronics than I already seem.

[vinceroger69]

Re: Samsung PN42B450B1DXA Turning On and Off Repeatedly

what ohms reading do you get between the 5 volt pins and ground? dead short?

[PirateFan06]

Re: Samsung PN42B450B1DXA Turning On and Off Repeatedly

Yea both are dead short.

[vinceroger69]

Re: Samsung PN42B450B1DXA Turning On and Off Repeatedly

What is the power supply board number

[PirateFan06]

Re: Samsung PN42B450B1DXA Turning On and Off Repeatedly

Looks like it's BN44-00273A.

[vinceroger69]

Re: Samsung PN42B450B1DXA Turning On and Off Repeatedly

This psu schematic may help you
https://archive.org/stream/Samsung_B...ge/n0/mode/2up

[PirateFan06]

Re: Samsung PN42B450B1DXA Turning On and Off Repeatedly

Thank you for this diagram. I will print it off tomorrow at work and work on it throughout the week. Hopefully I will have some good news next time I return!

[ReeceyBurger123]

Re: Samsung PN42B450B1DXA Turning On and Off Repeatedly

Unplug sus boards, does 5v short go away ?

[PirateFan06]

Re: Samsung PN42B450B1DXA Turning On and Off Repeatedly

Unplug sus boards, does 5v short go away ?

I had the board off the tv for a little while and tested it. I put the black probe on the screw mount of the board for a ground and the red probe to the 5.3 volt pin. Both 5.3v pins showed short on the multimeter.

[ReeceyBurger123]

Re: Samsung PN42B450B1DXA Turning On and Off Repeatedly

So that means your sus board is what is shorting the 5v not the Psu. Now all you need do it get a Pc psu apply 5v to the other end of the 5v fuse (not input) and put a pin to ground see what smokes remove that device and see if the short on the 5v rail goes.

[vinceroger69]

Re: Samsung PN42B450B1DXA Turning On and Off Repeatedly

I had the board off the tv for a little while and tested it. I put the black probe on the screw mount of the board for a ground and the red probe to the 5.3 volt pin. Both 5.3v pins showed short on the multimeter.

so are you testing the psu by its self with no other boards connected at all and the short is still there on the psu?

[PirateFan06]

Re: Samsung PN42B450B1DXA Turning On and Off Repeatedly

Yea I have the psu laying on the workbench with nothing attached and tested it. The 5.3v pins and the ground pins all constant "beep" when using the multimeter to check for shorts.

[PirateFan06]

Re: Samsung PN42B450B1DXA Turning On and Off Repeatedly

I put the board back on the tv and tested it. Grounded out until the tv turns on for a quick second then it reads 5.23v until the tv cuts itself off. Then back to being grounded out. Unplugged the x main and y main one at a time, and no change.