50" Mitsubishi Plasma TV

[aliasdck]

Model: PD-5010
Panel: NEC NP50C2MF01

The picture on this plamsa is fairly dark and grainy/snowy in appearance. The picture is not stretched fully to the screen on one side. This occurs on all inputs.

At first I suspected Y or X driver problem but now I don't think so because the osd/menu shows up correctly.

I am unfamiliar with the video processing circuitry. Any pointers?

I've found the service manual online but it'll cost about $10 to download... might buy it but I'll look around and see if I can find it for free first.

[cadiman]

Re: 50" Mitsubishi Plasma TV

correct but dim? driver problem x?

1)Look on scribd.com for info. I have found alot of info for l/g and panasonic on here free and real training manuals.

2)Wait for Wizard and Plainbill to respond

[aliasdck]

Re: 50" Mitsubishi Plasma TV

I was going to take some pictured and post them but I've been called out of town on business. This project will be on hold for a few days.

Cadiam:

The display is dim with some static like noise/grainyness. The osd and menu items show up bright and clear so I don't think its a buffer problem.

[PlainBill]

Re: 50" Mitsubishi Plasma TV

I was going to take some pictured and post them but I've been called out of town on business. This project will be on hold for a few days.

Cadiam:

The display is dim with some static like noise/grainyness. The osd and menu items show up bright and clear so I don't think its a buffer problem.

Something to think about: Does it occur on all inputs, or only on one? IIRC, this is a pretty early set; I believe it doesn't have any digital inputs.

Have fun storming da' castle!

PlainBill

[aliasdck]

Re: 50" Mitsubishi Plasma TV

Something to think about: Does it occur on all inputs, or only on one? IIRC, this is a pretty early set; I believe it doesn't have any digital inputs.

Have fun storming da' castle!

PlainBill

Can't sleep... hate being away from home.

The problem occurs on all inputs, and yes all inputs are analogue. Its an early set and probably not worth repairing but this is strictly a hobby for me at this point... I'm in it for the fun of it and for the learning experience.

[aliasdck]

Re: 50" Mitsubishi Plasma TV

I finally got some more time to play around with this TV today.

I was wrong in my original description of the problem. The OSD does not always show up correctly. It depends on what else is being displayed on the screen.

The TV will show a good display whenever the majority of the display is black. For example, my computer screen saver (black background with just the windows logo moving around) shows up perfectly. Colors are rich and vibrant. The OSD/Menu shows up bright and well defined during this time.

But the more the screen is filled up with bright colors (Especially white) the worse the picture gets. A full white background barely shows up at all. Lots of noise where the white should be and the display is very dark. When I bring up the OSD/Menu it shows up much dimmer than it should be.

Any idea if this is symptom of a bad panel, problems in signal processing, or panel driver problem?

[PlainBill]

Re: 50" Mitsubishi Plasma TV

I finally got some more time to play around with this TV today.

I was wrong in my original description of the problem. The OSD does not always show up correctly. It depends on what else is being displayed on the screen.

The TV will show a good display whenever the majority of the display is black. For example, my computer screen saver (black background with just the windows logo moving around) shows up perfectly. Colors are rich and vibrant. The OSD/Menu shows up bright and well defined during this time.

But the more the screen is filled up with bright colors (Especially white) the worse the picture gets. A full white background barely shows up at all. Lots of noise where the white should be and the display is very dark. When I bring up the OSD/Menu it shows up much dimmer than it should be.

Any idea if this is symptom of a bad panel, problems in signal processing, or panel driver problem?

The first place I would look is the power supply outputs. Also check the waveforms on the sustain cards.

PlainBill

[aliasdck]

Re: 50" Mitsubishi Plasma TV

The first place I would look is the power supply outputs. Also check the waveforms on the sustain cards.

PlainBill

I have checked the power supply outputs and they are correct and stable (both when the display looks normal and when it is bad).

I am unable to check waveforms on sustain cards... my scopes bandwidth is only DC to 10Mhz. I want to buy a used 200Mhz scope... maybe this is a good enough excuse to buy one.

[PlainBill]

Re: 50" Mitsubishi Plasma TV

I have checked the power supply outputs and they are correct and stable (both when the display looks normal and when it is bad).

I am unable to check waveforms on sustain cards... my scopes bandwidth is only DC to 10Mhz. I want to buy a used 200Mhz scope... maybe this is a good enough excuse to buy one.

Who needs an excuse to buy new test equipment?

PlainBill

[aliasdck]

Re: 50" Mitsubishi Plasma TV

Who needs an excuse to buy new test equipment?

PlainBill

Needed a good enough excuse to give to the wife





So I got a new scope and had a look at waveforms today. Not 100% sure what I am looking at here as I am not familar with NEC panels. I found a service manual for this tv but it does not provide any waveforms or service information for the y,x or z boards. It only contains service information for the power supply and logic boards.

But I am familiar with what the waveforms on an LG panel look like and I have been using them as a point of comparison.

The Y-sustain waveform looks good on this tv as far as I can tell. The x-sustain does not (assuming it should look somewhat like it does on a lg panel). In fact, the waveform seems to distort more and get noisy whenever the image is experiencing display issues.

I've replaced hybrid ic's in the past, but I'm not sure I'm going to go that route this time. I might just swap the board this time around.

[aliasdck]

Re: 50" Mitsubishi Plasma TV

Hooked up the scope again today and did some more investigating.

I must have been doing something wrong last time as both sustain waveforms look good. I had y sustain on channel 1 and z sustain on channel 2 and everything looks appropriate.

I'm beginning to suspect the control board. I followed the troubleshooting guide for an LG plasma set and it suggests the control board as well... (this display is NEC).

Guess I might buy a control board (logic board) but I'm not 100% sure this is the problem yet.

[Wizard]

Re: 50" Mitsubishi Plasma TV

You are not making any sense on description of fault.

Does picture looks like cut off top or bottom or sides (mainboard failing or panel itself especially Z drivers (columns) which are bonded to the panel (usually bottom, high end with 1920 lines sometimes have both top and bottom chips) which renders TV scrap) or compressed (scaler customer setting error)?

Cheers, Wizard

[aliasdck]

Re: 50" Mitsubishi Plasma TV

I have trouble articulating the symptoms so I must apologize...

The tv displays a perfect image whenever the majority of the display is black... for example, when there is a small logo on a black brackground. But when the majority of the display is a bright color then the image becomes noisy and dark. A full white screen is very dark and it appears the display is struggling to illuminate.

[mbates14]

Re: 50" Mitsubishi Plasma TV

basically from the sound of it, it sounds like your display panel is "starving for power" almost the same symptom you get on CRT when HV is low. sounds as if the Z sustain isnt having any output, or the power supply is weak and it cant hold the full current requirement of the display when full white.

[Wizard]

Re: 50" Mitsubishi Plasma TV

Much better description; check capacitors on SMPS and both X and Y boards.

May need a little tweak on Va and Vs if it is just sparkles (looks like pixie dust , sometimes red or green, blue is rare.). Panel draws least when on dark, full white is full power consumed.

Cheers, Wizard