Plasma TV image issues - Brand: Good Question

[aslee35274]

Hi guys,

My search for some sort of indication as to what is wrong with my tv lead me to this awesome thread:

https://www.badcaps.net/forum/showthread.php?t=18542

in which tom66 and a few others were helping out countless people out with diagnosing their tv issues.Most of the time the questioner was asked to start a new thread, so I thought I'd jump the gun and start off with a new thread.

I have a very cheap and low quality 50" plasma tv. The brand is 'DE', model number PDP-50x. I can't even find mention of this brand online, although all the boards seem to be sourced from Samsung. The tv has decided to die on me (surprise surprise haha) and probably should just be replaced, but I figured I'd see what I can find out.

While watching, the tv suddenly went white(ish), kind of like the saturation had been suddenly a drastically changed. The screen is now fuzzy. There are definite coloured 'sparkles' in dark areas, and lighter bits appear white. There is also a purple-ish tinge along the top of the screen.

I wasn't there when it changed, but according to my flatmates who were, there was no popping sound or anything. I've checked basics, such as fuses and key voltages, and also visually checked the capacitors. There was one on the y-sus board which had a suspicious bulge, but not enough for me to be confident it was faulty. I replaced it anyway, but it hasn't changed anything. All the others appear fine.

I was hoping someone could point me in the right direction? Even if it's not economically worth fixing, I'm interested in finding what's wrong, as I am a current mechatronic engineering student and enjoy the experience.

I have attached an picture or two of the tv's image, as well as the opened back.

Cheers again for any advice

[capkid]

Re: Plasma TV image issues - Brand: Good Question

Can you post the part numbers of the power supply, Y-Main, and X-main? It uses Samsung parts, and there is most likely a more common equivalent TV.

[aslee35274]

Re: Plasma TV image issues - Brand: Good Question

Power Supply: LJ44-00132A
Y-MAIN: PBA# LJ92-01299A/B/C/D
X-MAIN: PBA# LJ92-01500A

Let me know if any of these weren't the right numbers?

Cheers

[tom66]

Re: Plasma TV image issues - Brand: Good Question

This is similar to Samsung PS-50Q7/C7/Q97/C97HD.
You should start by checking the Vs and Va voltages. You will need a digital multimeter, do you have one?

[aslee35274]

Re: Plasma TV image issues - Brand: Good Question

Yea i checked Va, Vsc and Vs and Ve. All seemed to match what was recommended on the label in the back of the tv

[tn245]

Re: Plasma TV image issues - Brand: Good Question

I'm quite new at this but just got done working on a similar TV. There are some small 'littelfuse' fuses on Y-main and X-Main. They look like F5200 on the left of the attached pic.

Might be worth checking them to see if any are open. Mine was just the fuse, but it could indicate other components that have failed in the area.

Purplish tinge along the top makes me suspect top buffer chip? As I say I'm new at this. tom66 and others will point you in the right direction I'm sure.

[aslee35274]

Re: Plasma TV image issues - Brand: Good Question

thanks tn245, I will go and have a look when I get a chance

[aslee35274]

Re: Plasma TV image issues - Brand: Good Question

You seem to be onto something tn245, F5200 seems to have blown. Any hints as to what this would mean?

In case it's relevant, the capacitor that had a decent bulge on the top was C5709, near the power input of the y-main.

Again, thanks for the advice guys =)

[tn245]

Re: Plasma TV image issues - Brand: Good Question

I'd definitely check the FETs in that area for shorts. If it's like mine F5200 is protecting Q5200 which is a K2837 MOSFET. You can do a simple check in circuit with a diode test or ohmmeter for shorts and compare with the other K2837 lower on the board. I took mine out to test and it was fine. Also inspect buffer chips for any holes or burn marks and test for shorts like this: http://www.youtube.com/watch?v=5hVi5gd0aec

In my case everything seemed to test ok so I temporarily soldered in a fuseholer I had lying around with a 2A fuse to test and it worked.

[aslee35274]

Re: Plasma TV image issues - Brand: Good Question

From what I can tell, the MOSFET seems fine. There aren't any shorts in it at least.

The upper and lower buffers don't seem to have shorts either, based on the tests from the video you attached - thanks, it was very helpful. Also there are no visible defects on the ICs.

Although I say that after assuming that the pins that were live and ground were slightly different to the ones in the video. On the upper board, I had the lower three pins common, and the rest not. The lower board was the exact opposite. This lead me to assume that the configuration must be (for the upper) the three lower pins being live, and the remaining ground, and vice versa for the lower board. Does that sound valid?

So if the y-buffers are fine and the MOSFET is fine the blown fuse did its job, right? But does the fact that its blown indicate something wrong further upstream?

[tn245]

Re: Plasma TV image issues - Brand: Good Question

So if the y-buffers are fine and the MOSFET is fine the blown fuse did its job, right? But does the fact that its blown indicate something wrong further upstream?

Normally yes, but sometimes they do just blow it seems. As tom66 advised me, nothing to lose by trying a new fuse. I actually first put in a 1A fuse just to see if it would blow and it didn't and the TV worked fine. This is the second TV I've fixed where only a small fuse like this was the problem.

[aslee35274]

Re: Plasma TV image issues - Brand: Good Question

Well here's hoping then =). Cheers, I'll have a go once I can get hold of a new fuse and report back

[aslee35274]

Re: Plasma TV image issues - Brand: Good Question

Hey it worked! Wow I'm stoked. Couldn't get any access to littelfuses quickly, so ended up putting an equivalent glass fuse in with an in-line holder, as it looks like you did in your photo tn245?

My only question left is about the image quality. My quality (sharpness, sort of - smaller writing on the screen is fuzzy and unreadable) is noticeably lower than it used to be. Early on in my fiddling with the tv, I messed with the three trim pots on the ymain board. I thought I put them back where they started, but maybe not. Is it likely any of my component changing would lower the image quality? Or is it more likely a result of my messing with the ymain voltages?

If its not easilly fixable, I'm not too worried. The tv is watchable, which is a gigantic leap from what it was 24 hours ago, so I'm happy. Thanks heaps for all the advice, you guys are doing an awesome thing helping out inexperienced people like me who have a lot to learn =)

[tom66]

Re: Plasma TV image issues - Brand: Good Question

Misadjustment of those pots would cause maldischarge, which loosely means misfiring pixels. It probably wouldn't cause sharpness issues. You'd want to look into making sure you're using the exact resolution of the panel (probably 1365x768) and try to use HDMI over VGA, where available.

[aslee35274]

Re: Plasma TV image issues - Brand: Good Question

Ahh rookie mistake, forgot that I was testing the tv with the VGA plugged in, as my HDMI was broken. So all's good =). One last time, thanks to everyone for helping me get back to an up and running tv

[aslee35274]

Re: Plasma TV image issues - Brand: Good Question

Bugger, looks like I spoke to soon. After 2ish hours, the fuse blew again. So that means I'm looking for a failed component further upstream from the fuse that's causing the recurring issue. Any ideas?