First time poster in need of help and ideas Philips 42pf7320...

[mistamista]

Hello all. I found this forum at the suggestion of a friend who said that you guys are "bar-none, the most helpful folks on the web". After reading some other posts, I think it's fair to say that you guys are in a very good position to help me out.

So, I bought a Philips 42pf7320 about three years ago at a local repair shop who had recently replaced a few internal boards. It was working very well in his shop and the picture is astoundingly good...or was good anyway. The power supply died last month and I decided to go ahead and take the chance that the power supply alone would get it up and running. Suffice it to say that I was wrong.

The set turns on with both, the remote and power button as expected. I hear the "click" as the circuit breakers cycle on and I get a green LED that stays on regardless of how long I leave it on. The trouble is that it seems to go completely insane after about 30 seconds. The plasma screen flashes hundreds an hundreds of red and green pixels and does so in a rhythmic pattern until you shut it off. It doesn't have any issues with the power supply and I am reasonably certain that the "logic main" board and "X-main" board are in working order as they are nearly brand new. I'm unsure of the "Y-main", "Y-buffer" and "x-buffer" but none of the caps show any signs of damage and do not seem atypically hot to the touch.

Now, my concern is that I've gotten in over my head as I'm no troubleshooting aficionado, but I am very adept at working on electrons. I'm simply not sure where to begin the narrowing down of the failing parts. Do you guys have any ideas for me?

Thanks so much,
Michael

[cmj21973]

Re: First time poster in need of help and ideas Philips 42pf7320...

Service manual:


If not right SM then:
Look here for the one you need.
http://elektrotanya.com/

Photos:
1) Overall pic of the boards, in the set and connected.
2) Individual pics of each board. (component and solder side)

[tom66]

Re: First time poster in need of help and ideas Philips 42pf7320...

Sounds like Y-sustain failure. You could have tested the power board and verified that the power board was actually good before replacing it using a multimeter.

[mistamista]

Re: First time poster in need of help and ideas Philips 42pf7320...

Service manual:


If not right SM then:
Look here for the one you need.
http://elektrotanya.com/

Photos:
1) Overall pic of the boards, in the set and connected.
2) Individual pics of each board. (component and solder side)

I actually bought the long-form service manual, but I'm unable to track the board in failure as they all seem to show proper voltage and lack and visual component failure. Based on the info that I gave, would you feel confident that it's the y-sus board?

[mistamista]

Re: First time poster in need of help and ideas Philips 42pf7320...

Sounds like Y-sustain failure. You could have tested the power board and verified that the power board was actually good before replacing it using a multimeter.

Hi Tom and thanks. The power supply was going to be replaced either way. It had the faint smell of PCB board being cooked from the original failure...so it was due. Everything I can see leads me to believe that it
s the y-sus too, but I'm wondering if the Y-sus took the buffers too. Is there a means to test them other than the voltage? I ask because all of the components show proper voltage...but still, there's the pulsing blob of glowing red and green pixels.

One thing to add. I did a quick break down and rebuild this morning just to double check all of my connections, but everything was solid. But I tried something new and got a bit more info. When the pulsing pixels are on the screen, if I push the menu or PIP button on my remote, the pixels shift in volume and location. That sounds to me like a failed buffer set-up. Could it be both buffers and the y-sus?

[tom66]

Re: First time poster in need of help and ideas Philips 42pf7320...

Hi Tom and thanks. The power supply was going to be replaced either way. It had the faint smell of PCB board being cooked from the original failure...so it was due. Everything I can see leads me to believe that it
s the y-sus too, but I'm wondering if the Y-sus took the buffers too. Is there a means to test them other than the voltage? I ask because all of the components show proper voltage...but still, there's the pulsing blob of glowing red and green pixels.

One thing to add. I did a quick break down and rebuild this morning just to double check all of my connections, but everything was solid. But I tried something new and got a bit more info. When the pulsing pixels are on the screen, if I push the menu or PIP button on my remote, the pixels shift in volume and location. That sounds to me like a failed buffer set-up. Could it be both buffers and the y-sus?

Usually the problem you are seeing is caused by the ramp down MOSFETs not activating properly. So the pixels are firing randomly and chaotically, with a little control over the picture (which is typical.) Sometimes the buffers can be damaged by the sustain, and the buffers can also damage the sustain itself. It's advisable, unless you have an oscilloscope to test the sustain board, to replace the buffer(s) and sustain board at the same time with known good parts.

I notice though that it's not even a HD panel: it's just 852x480 pixels. It will probably cost a lot more than it's worth to repair, but it's your choice. You could buy a used 480p plasma for less than the price of the repair if you shop around.

[mistamista]

Re: First time poster in need of help and ideas Philips 42pf7320...

Usually the problem you are seeing is caused by the ramp down MOSFETs not activating properly. So the pixels are firing randomly and chaotically, with a little control over the picture (which is typical.) Sometimes the buffers can be damaged by the sustain, and the buffers can also damage the sustain itself. It's advisable, unless you have an oscilloscope to test the sustain board, to replace the buffer(s) and sustain board at the same time with known good parts.

I notice though that it's not even a HD panel: it's just 852x480 pixels. It will probably cost a lot more than it's worth to repair, but it's your choice. You could buy a used 480p plasma for less than the price of the repair if you shop around.

Thanks Tom. Yes, the TV is the older 720p standard, but I love using it on my video games and portable hard-drive media as it has excellent up conversion from SD to HD. I'd love to get a new set without a doubt, but this was a one-time trial that became a favorite pass-time. I think I'll see if I can find all three boards together at a shop or on a surplus website. The problem is that most of these sets die the same way, or so it seems.

Again, your time is very much appreciated.

Michael

[tom66]

Re: First time poster in need of help and ideas Philips 42pf7320...

Thanks Tom. Yes, the TV is the older 720p standard, but I love using it on my video games and portable hard-drive media as it has excellent up conversion from SD to HD. I'd love to get a new set without a doubt, but this was a one-time trial that became a favorite pass-time. I think I'll see if I can find all three boards together at a shop or on a surplus website. The problem is that most of these sets die the same way, or so it seems.

Again, your time is very much appreciated.

Michael

No, it's not even 720p; it's just 480p (slightly less than a standard PAL CRT, the same as a NTSC CRT.) That being said, I can barely tell the difference between 1080p and 720p at a 10ft distance, and 720p and 480p probably wouldn't matter too much to me as I don't watch that much HD. But for a HTPC 720p is a must. Anyway...

Do have a look around on craigslist for people selling off their old plasmas, it may be cheaper.