Samsung FPT5084X/XAA won't power on

[Cosmo66]

Hello good people!

So here's my story,

I picked up this Samsung 50" plasma from this chum who tells me that it won't power on. I bring the TV home and plug it in, it works beautifully for about 6 hours. I watched a couple movies on it, turned it off and on a few times in between to make sure.

The next day I go to turn it on.... .. nothing. No relay click, nothing at all except a flashing red light above the power switch.

I open the back of the TV and there are bad caps everywhere. I replaced 8 caps on the power supply, 6 on the Y sus. All fuses are intact. Still nothing. The power supply is not generating any voltages anywhere. When I measure the standby voltage with my DMM, it jumps around from 0 to 5 and everything in between. I swapped the main board with a "good" one I purchased on Ebay, but the problem persists. I also checked the relays, I placed 5 volts across them and they click magnificently.

Quite frankly, I am stuck on this one. Any help would be greatly appreciated.

[Cosmo66]

Re: Samsung FPT5084X/XAA won't power on

By the way, what is this vacuum tube looking thingy in the picture to the right of the blue cap?

It's right at the 120Vac input on the power supply board

[budm]

Re: Samsung FPT5084X/XAA won't power on

That is the surge suppressor Gas discharge tube, normally open circuit, will conduct when breakdown voltage is reached. The two small blues caps are safety caos X/Y type.
http://electronics.howstuffworks.com...protector2.htm

[mattpd]

Re: Samsung FPT5084X/XAA won't power on

Is it flashing any pattern? Maybe it has a bad solder joint and it temporarily fixed itself while transporting it.

[Cosmo66]

Re: Samsung FPT5084X/XAA won't power on

No pattern just steady flashing

[mattpd]

Re: Samsung FPT5084X/XAA won't power on

Most likely x or y boards since you already swapped the psu. Try turning it on with y board unhooked. If its a no go hook it back up and then try with x board unhooked. Some TVs will still come on and give you sound even with the boards out. If not, start unplugging boards one at a time from the psu to see if the voltages becomes steady.

[mattpd]

Re: Samsung FPT5084X/XAA won't power on

Err. I meant to say z or y boards.

[Cosmo66]

Re: Samsung FPT5084X/XAA won't power on

I powered it on with the x and y boards disconnected from the power supply and there are no voltages being generated anywhere. I have not swapped the power supply, I swapped out the main logic board I believe, the one with all the video inputs. I was suspicious of this board because I cannot get a steady 5V standby on the power supply.

[Cosmo66]

Re: Samsung FPT5084X/XAA won't power on

I meant I removed z and y boards....

[Cosmo66]

Re: Samsung FPT5084X/XAA won't power on

I am a little confused as to how the 5V standby gets generated, can anyone shed some light?

[tom66]

Re: Samsung FPT5084X/XAA won't power on

Check for cold joints on PSU.

[Cosmo66]

Re: Samsung FPT5084X/XAA won't power on

I just checked and resoldered about 80 joints on the power supply board. I did notice a couple joints that had completely detached from the board , but they were heatsinks.

One thing I noticed, while handling the power supply board, the components and heatsinks are too heavy for the flimsy board, and it tends to flex and bend as you move it around to work. I could literally hear creaking and joints pulling loose as I turned it around.

I really can't justify wasting anymore time or patience on this piece of $h!t. Throwing in the towel....

[tom66]

Re: Samsung FPT5084X/XAA won't power on

Put it on Craigslist for $50 then; someone will buy it and replace the PSU. On this model, the fault is almost always cold solder joints on the PSU. Do you know what a cold solder joint looks like?

[Cosmo66]

Re: Samsung FPT5084X/XAA won't power on

I sold it to some guy who said that's what he was gonna do. I just didn't want to replace the whole PSU for $100 after I saw blown caps on the Y and Z boards also. The TV was also missing a stand. Didn't seem worth the trouble

As for the cold solder joints, no what do they look like?

[tom66]

Re: Samsung FPT5084X/XAA won't power on

Here are some examples:
http://upload.wikimedia.org/wikipedi...der_joint2.jpg
http://softsolder.files.wordpress.co...der-joints.jpg
http://upload.wikimedia.org/wikipedi...lder_joint.jpg
http://www.kemo-electronic.de/images...loetstelle.jpg

They typically have a dull, grey colour to them, unlike other joints which appear shiny.