Samsung Plasma PN51D550C1FXZC

[tech2014]

The tv was working then all of a sudden the power went out and now all it does it click. I tested the voltages and they are almost 0 with all the boards connected. I removed the connector from the y-main board and the VA is 58 and and VS is 206 but quickly dropped down. When I reconnected the y-main and unplugged the x-main the voltages were good but dropped again. Does this mean I have a bad y-main board.

[tom66]

Re: Samsung Plasma PN51D550C1FXZC

Most likely, X-main.
Check across Vs and GND of X- and Y-main for shorts
(do this with power off, boards disconnected but installed in chassis)

[tech2014]

Re: Samsung Plasma PN51D550C1FXZC

Will do, thanks Tom. I will let you know what I find.

[tech2014]

Re: Samsung Plasma PN51D550C1FXZC

ok Tom, I found that the VS line is shorted on the x-main board. would it be easier to just order a replacement board or troubleshoot the board. Im good with either.

[tom66]

Re: Samsung Plasma PN51D550C1FXZC

Most likely you'll find a couple IGBTs shorted, should be repairable but fairly involved as you'll be replacing quite a few parts.
From what I've heard though this board is really hard to get hold of as a replacement. So repair might be the only option.

[tech2014]

Re: Samsung Plasma PN51D550C1FXZC

ok thanks Tom.

[tech2014]

Re: Samsung Plasma PN51D550C1FXZC

Wow Tom, you were right. I found 2 shorted IGBT on x main board. They are market 30G124. Now I just have to order the parts. thanks.

[newtothis]

Re: Samsung Plasma PN51D550C1FXZC

From toms reply as to the repair of the board I have a feeling it is going to take more than just those 2 IGBTs

[tech2014]

Re: Samsung Plasma PN51D550C1FXZC

The short on the VS line is now gone after the 2 IGBT parts were removed. I am also replacing the two driver ICs that control them.

[tom66]

Re: Samsung Plasma PN51D550C1FXZC

That's a good idea. Worth checking Y-main for shorts too in rare cases that can be damaged by a failure of the X-main. Also one suggestion is to power the repaired board up with a light bulb in series with Vs - this will limit any fault current. A 100W 240V bulb works well - may prevent damage to other parts if you miss something.

[tech2014]

Re: Samsung Plasma PN51D550C1FXZC

thanks Tom, I will do that.

[tech2014]

Re: Samsung Plasma PN51D550C1FXZC

Ok I got the parts, installed them and the tv still doesn't power up. The short is gone, but I noticed the VE is 0V. I didnt check this voltage at the start. Does anyone know where the VE comes from, smps or X or Y SUS

[tech2014]

Samsung Plasma pn51d550c1f VE too high

The VE voltage is supposed to be 80V, but I am getting 106V. Is there a pot for this like the VA and VS, or is it most likely a component on the y-sus board.

[tom66]

Re: Samsung Plasma PN51D550C1FXZC

It's generated on the X-main on most of these sets from linear regulation of the Vs supply. Rarely some panels generate it on the Y-main... Other sets generate a pre_Ve voltage which is high by ~20V this is then regulated to the required level by the X-main.

Short answer: it depends!

The Ve voltage is usually around 80-120V.

Make sure you have the control board ribbon cable installed.

Do you have an oscope available?

[tom66]

Re: Samsung Plasma PN51D550C1FXZC

Merged your threads together - we prefer the same TV/fault to stay in one thread. Ve may be only roughly regulated, or it may drop when a picture is displayed. There is usually an adjustment somewhere.

[tech2014]

Re: Samsung Plasma PN51D550C1FXZC

sorry for posting in 2 threads tom, won't happen again. The 120V VE was taken on the Y sus board. There is a VE test point on the X sus board but it reads 0V. There is a V_IN pin on the top connector on the x sus board, does this mean the VE comes off of the x main. All of the other voltages are present when the x-main board is removed from the circuit, albeit they are there for only seconds.

I do have a scope, but don't have an isolation transformer yet.

Does anyone know where to find the service manual. The ones I found don't have much.

[tom66]

Re: Samsung Plasma PN51D550C1FXZC

You don't need an isolation transformer for testing any panel-related parts on this TV. Only need it if working on the primary/HOT side of the power supply (the side connected to mains voltage)

It looks like this panel uses option 3 which generates a high-Ve on the Y-main, this is then regulated to the required voltage. They do this to reduce power dissipation in the regulation circuit on the X-main.

However, it's worth noting that Ve is only a bias voltage for the panel. The panel will display a picture - albeit a poor and dim one - without Ve. Do you have any image on the panel as it is? Might only be a very dim image visible in a dark room. But there should be one, if only the Ve is at fault.

[tech2014]

Re: Samsung Plasma PN51D550C1FXZC

Ok I found something very strange. When I remove the power from the circuit, the VE on the y main stays at around 90V and isn't discharging. Any ideas? Also, what can I check on the scope to troubleshoot .

[satinser]

Re: Samsung Plasma PN51D550C1FXZC

In the last few months I've had 2 of this model for repair both had blown 1GBTs on xsus. On the both occasions not only the 2x 30g124 had to be replaced but also the 2x RJP30H1 on the heatsink alongside. If you haven't already done so it might be worth checking them.

[tech2014]

Re: Samsung Plasma PN51D550C1FXZC

I did find 2 IGBTs shorted on the xsus, replaced them and short is gone, but still not powering up properly.