Riddled TV Repair Forum

oryan_dunn · Joined: 23 Jan 2013 Posts: 7

Make: Philips
Model: 30PW850H
Chassis: EM1.2U AA

I'm not sure exactly when this issue started, but I noticed on a completely black screen that the screen would be black, but the top would be lighter, which fades to full black about an inch down. It really looks like minor light leakage, like someon is shining a flashlight out of sight, and you see the reflected glow, if that makes any sense. I'll attempt to take a picture and post, but it may not turn out. I can also create something in MS paint that approximates the issue. I also noticed this on 2.35:1 movies, the upper black bar would be slightly lighter than the bottom. Also, you don't really noticed much during normal HD programming, but certain colors seem just a bit distorted in the area that you see the discoloration on the black screen.

So, I used the vertical amplitude control in the service menu to shrink the picture, and at the very top, regardless of input (signal, no signal) and scan rate (480i, 480p, 1080i), there is a very thin horizontal line, which is made up of a single red, then green, then blue line. Normally, this line is overscanned above the screen, so you don't see the line itself. But, I think the presence of the line is what's causing this discoloration (basically seems like light leakage at the top).

Far too many words, I'll get pictures of the line and attept a picture of the discoloration, but I'll probably need to generate an image approximating the issue.

Any ideas? I'm a software engineer with a minor in electrical engineering, so I'm very comfortable working in the set. I've discharged CRTs in the past. I also have the service manual for this chassis, which I can get to anyone willing to help.

Regards,
Ryan

Edit:
Ok, here's a simulated picture of what I see on a black screen:

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Edit 2:
Here's a simulated picture of what I see when I reduce the vertical amplitude down so the full vertical scan is shown. The very top has a horizontal line that's composed of one of each color as shown.

Uploaded with ImageShack.us

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oryan_dunn · Joined: 23 Jan 2013 Posts: 7

After playing around with it a bit more, I'm no so sure it's the line that's causing the discoloration. In the opening scene of Fellowship of the Ring, when the screen goes to black between the title, I noticed the brightness on the top and on the right side of the set. The lower left was still pretty black but the top and right sides seemed to have the black turn to a light gray.

oryan_dunn · Joined: 23 Jan 2013 Posts: 7

I've found this:
http://www.repairfaq.org/samnew/tvfaq/tvbccltras.htm
and this:
http://ths.gardenweb.com/forums/load/electronics/msg010215046854.html?12

Which would seem to indicate capacitors going bad.

Here's the service manual for my set:
https://docs.google.com/file/d/0B71t-o_uDecjNjJmZjEzOGQtMTNhNy00YmFjLWJlMWYtYTU3ZjMwNzg5ZGJm/edit?authkey=CISCj4kJ

Perhaps someone knowledgeable could look it over and see if anything jumps out as being a possible culprit. I plan on disassembling the set this weekend to look things over.

I've also noticed that after power-on for the first few minutes, there are "sparks" in the picture that happen all over the screen, usually one every few seconds or so. It's a strange spark or dot on the picture that causes it to tear from that location all the way to the right of the screen. After the set has warmed up, these go away. I can't help but thinking all of these problems are somehow related, probably to a capacitor or two going bad.

oryan_dunn · Joined: 23 Jan 2013 Posts: 7

After a bit more testing, and picking up a used 34PW8502 off craigslist, I don't think the line at the top has anything to do with the slightly brighter picture at the top. The new TV also has a similar line if you reduce the size, but it doesn't seem to have the same brightness issue. I've also noticed that the same brightness issue occurs on the right side of the screen. Any ideas what component could cause this? It almost seems like it'd be something in the defelection, but I don't know enough to properly diagnose the issue.

I got the 34PW8502 to possibly take the internals out and put in the 30" set that I have. I think most things would work, but the 34" has an issue that I'll start a new thread for. Once I get that fixed, I'll swap the parts out.