Issue with Samsung PS50c450 Plasma 50" no power up

[edgimeno]

Hi there!!
I just bought this TV yesterday, "as is". owner said "nothing happens when you hit the power button".
Ok I got it home, connected to mains. Relays click back and forth 5 or 6 times, during 5-10 seconds, led blinks, and after that led stays on, relay stop and it wont respond to either remote or panel turn on command

Opened it up
Nothing seems burned, no bulged capacitors, nothing leaked (aparently).

Checked Power supply: 5V stdby are there, nothing else (15v, 5v3 are off)
Makes sense as the TV is "officially" off
Force PS_ON to GND and nothing happens.

Whenever I disconnect either the cables from X-main to Y-main, or the power supply to y-main, it powers up with the startup tune normally (no image as the Y-main is unplugged), but the from led reacts to the remote commands.

Is this normal? Bad power supply? Bad Y-main? What else can I check? I checks Vs and I get (normal) 213V so maybe PS if OK

Thanks in advance!

So

[edgimeno]

Re: Issue with Samsung PS50c450 Plasma 50" no power up

Also If I unplug the Ymain from it's buffer board (slide it out of the 4 connectors), nothing changes (tv doesn't power on) when the Y main is powered. So this leads me to think that the issue is not in the buffer.
So should I go and change the Y-main? It seems like a hard to troubleshoot board with lots of components on the bottom side too.
Its model lj41-08458a
15€ + 6€ shipping, not bad, I just don't want to waste the time it would take to get here if it's not that board
Is it common for Y boards to get bad and lock the whole TV preventing it to power up? Is there anythign easy to diagnose on these boards?

Thanks!!

EDIT: I took one by one all the pins in the power to Y-sus plug, and the issue is the Vs lead. I insert one by one GND->Va->Vg and everything so far stays on, but as soon as I insert the Vs pin, I get a spark and it turns off, so there's got to be a large shortcut somewhere in the Y-sus board related to Vs , right?

EDIT2: Sorry Im progressing on the board as I write here. Vs goes from power supply to Y-main, and then from Y-main to X-main. If I measure Vs normally I get 0ohm to GND, so I suspecting a shortcut in Y-main, but if I unplug X-main from Y-main, the shortcut is no longer there. Removed X-main from panel and I measure the shortvut between Vs and GND. It seems easy to diagnose now as it power only 2 sections, sets of mosfets in the powersink, and some other components. Gona isolate them all now

[sordids999]

Re: Issue with Samsung PS50c450 Plasma 50" no power up

PICTURES !!
showing all the boards will hopefully help you more to fixing your problem

[edgimeno]

Re: Issue with Samsung PS50c450 Plasma 50" no power up

Hold on...Im about to fix it LOL...traced the shortcut in X main isolating aread (good thing there are several jumpers to cut and resolder)
I JUST desoldered the "offending" component. RJP30E2 mosfet...
It has a clear shortcut among all 3 pins. Shortcut in the board is gone now.
Goind to see what the quickest place to have it sent here

Thanks!!

[sordids999]

Re: Issue with Samsung PS50c450 Plasma 50" no power up

opps second post was not showing when i posted

[edgimeno]

Re: Issue with Samsung PS50c450 Plasma 50" no power up

No worries, I should probably delete this post as I found the issue quickly but I guess it may still be useful to someone else later
Symptom: 50" plasma Samnsung TV not turning on. Relay clicks "on" them clicks back "off"
Opened TV: Removed power cable from PS to Y-main. TV would start on (startup tune)
Plug power to Y-main. Unplug Y-main to X-main. TV still starts up
Remove all wires in X-main. Check between Vs and Gnd in X-main. Got 0 Ohm
Removed X-main. Vs doesn't go to many components. Isolated one by one.
Caps->Checked good
Diode on heat sink->Checked good
-IGBT mosfet on heatr sink. Had shortcut on all 3 pins. Replaced
(Hopefully) this is it, will get back in 3 days (what takes the delivery of this component)

[tw2005]

Re: Issue with Samsung PS50c450 Plasma 50" no power up

No worries, I should probably delete this post as I found the issue quickly but I guess it may still be useful to someone else later
Symptom: 50" plasma Samnsung TV not turning on. Relay clicks "on" them clicks back "off"
Opened TV: Removed power cable from PS to Y-main. TV would start on (startup tune)
Plug power to Y-main. Unplug Y-main to X-main. TV still starts up
Remove all wires in X-main. Check between Vs and Gnd in X-main. Got 0 Ohm
Removed X-main. Vs doesn't go to many components. Isolated one by one.
Caps->Checked good
Diode on heat sink->Checked good
-IGBT mosfet on heatr sink. Had shortcut on all 3 pins. Replaced
(Hopefully) this is it, will get back in 3 days (what takes the delivery of this component)

I had more than one shorted plus a pair of 20Amp N FETs shorted too, threw in something temporary to test. First time it lasted 1 minute, then used a pair of Toshiba IGBTs with higher voltage and current rating. Lasted an hour.

Board Heatsinks were very hot, suspect other components bad like driver ic, don't know as I usually don't try component on Samsung.

Hope you have more luck, don't be surprised if it goes pop again.

Also have a good look for cracked solders , I found on the fets one leg was completely cracked and floating.

[edgimeno]

Re: Issue with Samsung PS50c450 Plasma 50" no power up

Will check that. Hopefully there's nothing bad beyond the IGBT, will know at the end of this week

[edgimeno]

Re: Issue with Samsung PS50c450 Plasma 50" no power up

No dice...Unfortunately, I got the IGBT in my mail yesterday, soldered it, and...something strange happened.
Put it all back in place. Turned TV on. The relay clicked on and off, like when it was shorted. Tired to turn on again, Samsung tune played but screen was black. It all responded to remote commands (I mean the led flashed but screen was still black).
Checked the back side again and noticed 2 things:
-VS is gone. But in this case no matter what board I disconnect from the PS (Y sust, X sust), nothing changes
-This is worse, I get nothing at all (no startup flashes, nothign later) at the LOGIC board LED. It's just off all the time.

I remember this led used to flash at different rates when the Y-sust was shorted or when it was disconnected, but now, even if I unplug EVERY ribbon (except the one from the PS) in the logic board, nothing lights up in it

Did I fry it? Is is the PS now? How should I proceed to diagnose it without starting to just purchase boards randomly

BTW this LOGIC board is a LJ92-01705

[edgimeno]

Re: Issue with Samsung PS50c450 Plasma 50" no power up

Nobody? Should I try to manually short PS_ON to ground and/or VS_ON to Vcc? And see what happens? Thanks!

[edgimeno]

Re: Issue with Samsung PS50c450 Plasma 50" no power up

Bump...anyone? Thanks

[chrismurphy]

Re: Issue with Samsung PS50c450 Plasma 50" no power up

Think you should give up ..I dont think you dont have enough knowledge to proceed in safe manner
Replacing boards randomly will cause you grief and will be costly

[edgimeno]

Re: Issue with Samsung PS50c450 Plasma 50" no power up

Think you should give up ..I dont think you dont have enough knowledge to proceed in safe manner
Replacing boards randomly will cause you grief and will be costly

I dont know why youre saying that, I do have electronics knowledge but no experience on plasma TVs, thats why Im asking for help so I dont have to start swapping boards randomly. I already found a shortcut in my Ysus board and fixed it, but since then something else gave up and now I dont even have power in my logic board, I just need some directions on how to proceed to diagnose whats wrong

[maxvalutech]

Re: Issue with Samsung PS50c450 Plasma 50" no power up

Do a search for Samsung Tech Talk issues around 2010/2011 .

[tw2005]

Re: Issue with Samsung PS50c450 Plasma 50" no power up

I'm a bit muddled with what you're saying. You probably need some cheat sheets or troubleshooting guides to help. Samsung expert I am not but I think this series if either x or y disconnected Vs will not stay on. You would have to have the probes on as you strat it and it may be there for a second but it will shut down straight away.

As for the logic board can you state what is connected and what is not?

Also you can kill the ymain sometimes with a bad X. I did that in the 42" version after trying to repair.

[edgimeno]

Re: Issue with Samsung PS50c450 Plasma 50" no power up

Thanks but in my cae, after repairing the X, I reassembled averything and realized that nothing worked, unplugged X and Y, and still don't get Vs and T-con seems to be completly off, my question is, how do I test if this is due to PS failure to power T-CON, o the T-CON itself?
Thanks

[tw2005]

Re: Issue with Samsung PS50c450 Plasma 50" no power up

Thanks but in my cae, after repairing the X, I reassembled averything and realized that nothing worked, unplugged X and Y, and still don't get Vs and T-con seems to be completly off, my question is, how do I test if this is due to PS failure to power T-CON, o the T-CON itself?
Thanks

So if power is disconnected from the x and y are the ribbon cables that go from the Logic Ctrl board ( you call it tcon) to x and Y disconnected? have you tried turning it on like that?

[tw2005]

Re: Issue with Samsung PS50c450 Plasma 50" no power up

Have a look at this and see if this looks like your setup

[edgimeno]

Re: Issue with Samsung PS50c450 Plasma 50" no power up

Yes, I totally isolated X and Y boards, removed EVERY wire from /to them (like f they were out of the chassis). Only PS, Main, and T-COn. I turn TV on, hear the Samsung chime (so at least SOMETHING in PS is alive and Main is alive), but I get no Vs, no Vg, no Va...Is T-COn dead? How can I test "whose fault this is"?

[tw2005]

Re: Issue with Samsung PS50c450 Plasma 50" no power up

Yes, I totally isolated X and Y boards, removed EVERY wire from /to them (like f they were out of the chassis). Only PS, Main, and T-COn. I turn TV on, hear the Samsung chime (so at least SOMETHING in PS is alive and Main is alive), but I get no Vs, no Vg, no Va...Is T-COn dead? How can I test "whose fault this is"?

Is the green activity light blinking on startup?