Testing the PDP idea. Will it work?

[Skipfinder]

Samsung PN50C490B3DXZA
I have only the bottom 1/6th of the screen functioning even after replacing the Y Main and buffer boards. I'm thinking that before I throw any more money at this set that I'd like to verify that the PDP isn't bad. All voltages are good.

Here's my idea:
Remove both Y boards from the chassis but provide solid grounds from the boards to the chassis. Move the 6 buffer ribbons up one position, leaving the top ribbon disconnected and no input to the bottom of the screen. I know the bottom ribbon is providing good signal to the PDP. If the image moves up the screen by 1/6th then I know the PDP is good.

Will this work?

[tom66]

Re: Testing the PDP idea. Will it work?

The PDP is good anyway, there is no way a bad PDP could cause that issue, you have a bad buffer chip either bottom most or 2nd from bottom.

[Skipfinder]

Re: Testing the PDP idea. Will it work?

I guess it's possible that the new buffer board has the same bad chips as the one I replaced, but it isn't likely. The new Y main and buffer boards are factory fresh from ShopJimmy, and the exact same symptoms remain. I replaced them as a pair and verified that the voltages are in spec.

I have the bottom 1/6th of the screen working normally, and about 2" of the top of the screen working on every other line. The edges of the black area are clean and square. I've tried different inputs on the main board to no avail. The logic board is blinking once per second. All voltages are correct and the set turns on and remains on as it should.

I've never worked on a plasma TV before so this is kinda fun. I'm a EE but this is out of my range of experience. I couldn't believe how few boards were in this 2010 model. So simple inside!

[tom66]

Re: Testing the PDP idea. Will it work?

Can you post a picture of the fault?

[Skipfinder]

Re: Testing the PDP idea. Will it work?

The bottom of the screen is clear and normal. The top the screen is displaying on every other line. Everything else is dark.

[tom66]

Re: Testing the PDP idea. Will it work?

I may have to change my opinion. I've seen some cracked plasma panels with that symptom. Any signs of cracks on the plasma screen?

[Skipfinder]

Re: Testing the PDP idea. Will it work?

No cracks in the screen and no noise from the screen. It hasn't been moved since the day it was brought home.

[tom66]

Re: Testing the PDP idea. Will it work?

If you replaced the buffer board, I can't see anything other than a bad panel causing this fault.
I don't think your trick will work properly due to the need for a solid ground but it's worth a shot.

[Skipfinder]

Re: Testing the PDP idea. Will it work?

I've got nothing to lose at this point. I'll let everybody know how it turns out.

[Skipfinder]

Re: Testing the PDP idea. Will it work?

Well, that was anticlimactic. I suspect that the outputs to the buffer ribbon connectors aren't all the same, because I didn't get an image further up the screen like I'd hoped to see. I did however get random lines across the screen area that was formerly completely black, so that gives me hope that the PDP isn't damaged. I'm starting to wonder if the main board isn't outputting a complete image, if that's even possible.

[freakaftr8]

Re: Testing the PDP idea. Will it work?

I really dont think the mainboard can cause that issue . Unfortunately. With the power off look closely at the screen at the very beginning of the y buffer ribbons inputting into the screen. Almost the first pixel on that side. Do they look black? Compare these pixels with the pixelswith then section of the screen that works.

[freakaftr8]

Re: Testing the PDP idea. Will it work?

Also since you tried this setup have you tried putting a dead ribbon on tje good section to see if you get a pictire as well? I know itsnnot a good idea but hell mighy as well try. If it works that will be interesting. I almost want to say replace both y buffers and y board at the same time. But it looks like you did that already. Did you try thennew y main and buffers at the same time?

[Skipfinder]

Re: Testing the PDP idea. Will it work?

I'll look at the pixels tomorrow and let you know. Thanks Freakafter8.

[Skipfinder]

Re: Testing the PDP idea. Will it work?

Also since you tried this setup have you tried putting a dead ribbon on tje good section to see if you get a pictire as well? I know itsnnot a good idea but hell mighy as well try. If it works that will be interesting. I almost want to say replace both y buffers and sc board at the same time. But it looks like you did that already. Did you try thennew y main and buffers at the same time?

Do the ribbons come off the PDP? I figured that they were integral. If they come off I'm willing to try anything. I put the known good signal to a dead section. It didn't work, but I DID get some random screen activity and the faint glow of power in the dead section. It gives me hope that the screen is OK.

And yes, I replaced both the Y main and the Y buffer (it's all one buffer board) at the same time and verified the voltages to and on the board were correct.

[freakaftr8]

Re: Testing the PDP idea. Will it work?

If you got anything in that area the p anels gotta be good. No the ribbons do not come off the panel.

[freakaftr8]

Re: Testing the PDP idea. Will it work?

A shot in the dark but maybe someone with more experience than I do can chime in. Possibly a control board issue?

[tom66]

Re: Testing the PDP idea. Will it work?

Try doing the test pattern jumper
https://www.badcaps.net/forum/showpo...61&postcount=2

[Skipfinder]

Re: Testing the PDP idea. Will it work?

The LVDS cable should be a twisted pair cable, right? I don't remember seeing one but I'll take a look when I get back to the set. Regardless, it should connect the power supply and main board?

The Samsung Fast Track guide for the PN50C490B3DXZA says that I also have to jumper the PS-On pin to its circuit ground. I'm thinking that it must be a 15Vamp circuit.

[tom66]

Re: Testing the PDP idea. Will it work?

LVDS runs from control board to main board. If you post a pic of your control board we can highlight which cable is LVDS.

[Skipfinder]

Re: Testing the PDP idea. Will it work?