Samsung PN42C450 - Working my way through the diagnosis

[MrBerga]

Hi all,

Long time lurker, first time poster. My 42" Samsung plasma TV does not power on; instead a series of relay clicks are heard. I've formed my conclusion and want to bounce ideas off you guys. No bulged, discolored, smelly, or otherwise incorrect-looking caps or ICs anywhere.

What I know:
-After disconnecting all other boards to SMPS except the Logic Board, relays click twice and remain off. I can "force" the SMPS to go on my jumping PS_ON to GND.
-Doing this causes 5.4VDC and 15VDC in the correct places, but no voltage at Va/Vs
-Plugging in both the Logic Board and Main Board yields no Va/Vs.
-Plugging in both the Logic Board and Main Board and jumping PS_ON to GND does yield Va/Vs at the test points, and the voltage is perfectly in-spec.

Based on this, I would presume the Main Board is bad. When only Main Board is plugged into SMPS, relays should power on fine, correct?

I'm new-- let me know what other information I can give to help out!
Thank you!

[randtek]

Re: Samsung PN42C450 - Working my way through the diagnosis

If you look at post #11 of this thread:
https://www.badcaps.net/forum/showthread.php?t=19522&
I give a procedure for testing that may help you confirm the main board as your problem.

[MrBerga]

Re: Samsung PN42C450 - Working my way through the diagnosis

Randtek: Thanks, that was extremely helpful. I used it to find myself a new diagnosis...

What I know now:
-When all cables are plugged in EXCEPT for power to the X-Main-Drive, the TV powers on normally and even chimes and displays static for a second.
-Va/Vs voltages begin at typical values, however when the display turns off, the voltages return *slowly* back to zero.

I'd be inclined to conclude that my X-drive has failed. However, because the power is actually routed through the Y-drive, I can't be sure the Y-drive isn't to blame... Is there a way to know for sure? Also, why am I seeing incorrect Vs/Va voltages?

In the first attached photo, you can see the connector I need to unplug in order to get the static to display. I hope I have my naming right but feel free to correct me :-)

[Mt.Man]

Re: Samsung PN42C450 - Working my way through the diagnosis

X-main is a common failure on that panel. Make sure you update the software also after you get it running to help prevent the x-main from failing again.

[tom66]

Re: Samsung PN42C450 - Working my way through the diagnosis

Yes I have repaired this same model with failed X-main. Usually you will see a dim picture with it removed.

[MrBerga]

Re: Samsung PN42C450 - Working my way through the diagnosis

Usually you will see a dim picture with it removed.

I have a similar defect but not the same. My display turns on for about a second and shows static. I am unsure whether it's normal brightness.

I have no Vs/Va voltage when X-Main is not connected. Is it normal for the X-Main to "drive" the SMPS to provide Vs/Va?

[tom66]

Re: Samsung PN42C450 - Working my way through the diagnosis

No, SMPS provides Vs/Va.

When X-main fails it shorts, killing Vs/Va voltage until it is removed.

Does screen look like this? My video when I repaired this TV:
https://www.youtube.com/watch?v=Bmu12mCOKcU

In my case the X-main partially failed, but after running it for some time, it eventually shorted. I replaced it, and I fixed the TV.

[MrBerga]

Re: Samsung PN42C450 - Working my way through the diagnosis

Hey Tom66, what component(s) did you replace on that particular X-drive board? I'll pull that board out and look at it more closely.

Additionally: the troubleshooting manual below describes scenarios for certain failures...
Red tint: X drive failure
No picture: Y drive failure

Is this reliable? I have a (staticy) picture but only momentarily. Uploaded a lousy shot of the static.