PN50B400P3D 50" Samsung Plasma Won't Turn On.

[tom66]

Re: PN50B400P3D 50" Samsung Plasma Won't Turn On.

Unplug Y-buffer, does -Vsc rise?

[Dowd, Elwood P.]

Re: PN50B400P3D 50" Samsung Plasma Won't Turn On.

unplugged the Y-buffer & no change

I'm putting the red lead on the VSC point & the black lead to the chassis screw. The same as I did on the other test.

[tom66]

Re: PN50B400P3D 50" Samsung Plasma Won't Turn On.

If that is the case, your (new) Y-main is bad.

[Dowd, Elwood P.]

Re: PN50B400P3D 50" Samsung Plasma Won't Turn On.

Could the adjustment screw be turned all the way down? Could something else be bad & have fried the new Ymain when I put it in?

[tom66]

Re: PN50B400P3D 50" Samsung Plasma Won't Turn On.

You can test your Y-buffer.
The min -Vsc is not 0V (more like 60% of max), but you can try adjusting it anyway.
https://www.youtube.com/watch?v=51SZsfH60EY

[Dowd, Elwood P.]

Re: PN50B400P3D 50" Samsung Plasma Won't Turn On.

I pulled the Y-buffer & tested it according to that video. I dont have a sound option on my meter. I have it set on diode. I get a reading of .8-1.5 on most pins. Is that the correct setting I should use? What reading would indicate a fault?

[tom66]

Re: PN50B400P3D 50" Samsung Plasma Won't Turn On.

I would try using ohm mode - internal diode bias of meter may give incorrect results. Also make sure you get probes around same way as I did in video.

[Dowd, Elwood P.]

Re: PN50B400P3D 50" Samsung Plasma Won't Turn On.

Is the Y-sustain output a certain pin or connector or all 4 connectors? My Y-buffer board is LJ41-07018A

[tom66]

Re: PN50B400P3D 50" Samsung Plasma Won't Turn On.

Usually it's the connector where all the pins are grouped. There are several lots, -Vsc(floating GND) and Vof(output), the output path is the main output from the Y-main and has the most pins due to the higher current. Typically you want to test from the output to each of buffer outputs. That being said I would not expect a bad buffer on these newer Samsungs to damage a Y-Main and I suspect the board you got was defective.

[Dowd, Elwood P.]

Re: PN50B400P3D 50" Samsung Plasma Won't Turn On.

Ok, thanks. I'm going to borrow a different meter to check it, I don't quite trust mine for something like this.
I haven't bought any new boards before so I don't know how often you get a bad one but I would hate to put another one in & fry it as well if there's another problem.

[tom66]

Re: PN50B400P3D 50" Samsung Plasma Won't Turn On.

What you can try if you get a new board is to test it without the Y-buffer connected. That being said, these Y-main boards can usually handle a shorted -Vsc without damaging themselves. They just go into protection mode.

[Dowd, Elwood P.]

Re: PN50B400P3D 50" Samsung Plasma Won't Turn On.

Alright, Thanks. Just out of curiosity, I put the old Y-main back in disconnected from the X main & Y buffer. It read -190 VSC. I reconnected everything & it still read -190 VSC. Does this change anything or are the two Y-mains still bad but in different ways?

[Dowd, Elwood P.]

Re: PN50B400P3D 50" Samsung Plasma Won't Turn On.

I put the new Y-main back in & tested off the "side" of the VSC test point instead of the center & it reads -188. It's supposed to be -193. Still no change in the picture.

[tom66]

Re: PN50B400P3D 50" Samsung Plasma Won't Turn On.

That does change things, what happened for it to go from 0 to -190V? Can you try with buffer board installed?

[Dowd, Elwood P.]

Re: PN50B400P3D 50" Samsung Plasma Won't Turn On.

I tested it with everything connected & it still read -188.

It it reads 0.00 with the lead like this


It read -188 with the lead like this

[Dowd, Elwood P.]

Re: PN50B400P3D 50" Samsung Plasma Won't Turn On.

It must not get a good enough connection for some reason in the center, I cleaned it with alcohol but it didn't change. I assume the VSC was always -188, I just failed to get the reading.

[tom66]

Re: PN50B400P3D 50" Samsung Plasma Won't Turn On.

OK. Different tact. If you look at the control board there should be an LED on it. The LED will either blink once a second or light for 5 seconds and dark for 2 seconds, what does it do?

[Dowd, Elwood P.]

Re: PN50B400P3D 50" Samsung Plasma Won't Turn On.

It stays on for about 3 seconds then goes out. I only left the tv on about 20 seconds but it never came back on.

http://www.youtube.com/watch?v=5ZCNn...u812QMYbQkxRWQ

[tom66]

Re: PN50B400P3D 50" Samsung Plasma Won't Turn On.

Well, it sounds like the control board is shutting down but not going into its fault state indicated by 5s on - 2s off. I don't know if these older Samsungs do that, for sure. But the LED should blink once a second if the system is working. I can suggest a control board replacement but I'm not confident it will fix it.

[Dowd, Elwood P.]

Re: PN50B400P3D 50" Samsung Plasma Won't Turn On.

The buttons on the front (power, channel, volume, etc..) are non responsive. Are they related to the control board?
Seems like it's either the control board or the power supply board at this point.
I found a used control board for $13. I think I'll order it & if that doesn't fix it, try a PSB.