Problem with red on a Panasonic TV. - Electronic Circuits Projects Diagrams Free

Hero999 · 26th September 2006, 10:50 AM

The picture has remained clear, but over the last few months the red has been deteriorating. First it went out of focus, then it started to get dimmer and dimmer, now it's practically non-existant.

The TV doesn't have a RGB colour adjustment setting, but it does have an overall colour setting which I've set to the maximum value. This did make a small difference but not anymore.

Is there a way to adjust the TV using service mode or is the red electron gun totally nackered in which case I assume we need a new TV?

**Nigel Goodwin** · 26th September 2006, 10:58 AM

Modern TV's (last 20+ years?) use decoder chips with 'automatic greyscale adjustment' - this means they automatically adjust the three colours 50 times a second to maintain the picture quality. But what this means is that you don't really get a gradual deteriation - it keeps correcting itself until eventually it runs out of adjustment range, then all of a sudden you see a problem.

There are manual adjustments, which may help get it back within auto-range?, but these will be accessed from service mode - not actual pots.

Hero999 · 26th September 2006, 04:17 PM

The TV was bought about 1997 and has fully digital tuning, brightness and contrast controls..

How do I access service mode on this machine?

**Nigel Goodwin** · 26th September 2006, 04:21 PM

Quote:

Originally Posted by Hero999

The TV was bought about 1997 and has fully digital tuning, brightness and contrast controls..

How do I access service mode on this machine?

No idea?, you've never even mentioned it's model number!.

Hero999 · 26th September 2006, 04:49 PM

I don't know the model number, I'll have a look.

It's a TX-29AD2.

**Nigel Goodwin** · 26th September 2006, 05:18 PM

Here's how to access service mode.

Hero999 · 26th September 2006, 05:28 PM

Thanks for the information, where did you get it from?

It's just a pain in the bum because I can't find the origional remote!

Luckilly it looks as if it might work with the new generic remote, so I'll have a go.

**Nigel Goodwin** · 26th September 2006, 07:04 PM

Quote:

Originally Posted by Hero999

Thanks for the information, where did you get it from?

I got it off the PDF of the service manual - which is just a scanned one, not a 'real' PDF, due to the age of the set.

StarBaseONE2 · 2nd October 2006, 05:14 AM

Discover the chips numbers and attempt to get the specs on this chip. You will find that it will have a R, and G, and B input pins. In the circuit supply to the R input you will likely find a small (in value) capacitor. I would bet that it will have a high ESR. If you have no way to test the ESR a sustitution of this cap would be wise. If this circuit tests healthy,or you find cap substitution does not correct the problem. I have seen a resistor change value on the CRT board (CRT board plugs into the picture Tube) to cause this as well.

I (in my opinion as a TV tech)would stay out of the service menus until this approach has been determined not to work!

Good Luck,

HiTech · 2nd October 2006, 08:51 PM

set the color all the way to minimum and note how the picture looks. B&W should look obviously proper. If not it may be screen drive adjustment, to weak crt gun issues.

Hero999 · 2nd October 2006, 10:04 PM

Lol, I've still got to get around to doing this.

I think I'll try the service menus first because I don't w3ant to risk messing it up when I open the case.

HiTech · 3rd October 2006, 02:58 PM

you don't need the service menu to do what I mentioned. Simply turn the color setting to its minimum and note what the pic looks like in black & white. It should look true and no hints of R, G, or B tint to it. If B/W looks true then the crt isn't the culprit.

Hero999 · 5th October 2006, 09:07 PM

I see what you mean now. I'll give it a go!

Hero999 · 8th October 2006, 01:43 AM

I turned the colour down to minimum and it still looked white, but there again there is some red present so it will still look white. I think it's probably the tube or an associated circuit since the menu screens are still in colour and the red appears to be very dark, the yellow looks slighty greenish and the magenta is violet.

Hero999 · 10th October 2006, 10:15 PM

Am I right then?

Does anyone agree that tube is probably worn out?

I'd like to be at least 90% sure nothing can be done before we dump it and buy a new one.

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26th September 2006, 10:50 AM	#1
Hero999	Problem with red on a Panasonic TV. The picture has remained clear, but over the last few months the red has been deteriorating. First it went out of focus, then it started to get dimmer and dimmer, now it's practically non-existant. The TV doesn't have a RGB colour adjustment setting, but it does have an overall colour setting which I've set to the maximum value. This did make a small difference but not anymore. Is there a way to adjust the TV using service mode or is the red electron gun totally nackered in which case I assume we need a new TV? __________________ I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong. Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.

26th September 2006, 10:58 AM	#2
Nigel Goodwin	Modern TV's (last 20+ years?) use decoder chips with 'automatic greyscale adjustment' - this means they automatically adjust the three colours 50 times a second to maintain the picture quality. But what this means is that you don't really get a gradual deteriation - it keeps correcting itself until eventually it runs out of adjustment range, then all of a sudden you see a problem. There are manual adjustments, which may help get it back within auto-range?, but these will be accessed from service mode - not actual pots. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

26th September 2006, 04:17 PM	#3
Hero999	The TV was bought about 1997 and has fully digital tuning, brightness and contrast controls.. How do I access service mode on this machine? __________________ I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong. Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.

26th September 2006, 04:49 PM	#5
Hero999	I don't know the model number, I'll have a look. It's a TX-29AD2. __________________ I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong. Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.

26th September 2006, 05:18 PM	#6
Nigel Goodwin	Here's how to access service mode. Attached Thumbnails __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

26th September 2006, 05:28 PM	#7
Hero999	Thanks for the information, where did you get it from? It's just a pain in the bum because I can't find the origional remote! Luckilly it looks as if it might work with the new generic remote, so I'll have a go. __________________ I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong. Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.

2nd October 2006, 05:14 AM	#9
StarBaseONE2	I would start with the Video processor... Discover the chips numbers and attempt to get the specs on this chip. You will find that it will have a R, and G, and B input pins. In the circuit supply to the R input you will likely find a small (in value) capacitor. I would bet that it will have a high ESR. If you have no way to test the ESR a sustitution of this cap would be wise. If this circuit tests healthy,or you find cap substitution does not correct the problem. I have seen a resistor change value on the CRT board (CRT board plugs into the picture Tube) to cause this as well. I (in my opinion as a TV tech)would stay out of the service menus until this approach has been determined not to work! Good Luck, __________________ ...Located on the fringes of the Cosmic CoastLine... .....Deep, Deep, in the Engineering Section... .......StarBaseONE2 Last edited by StarBaseONE2; 2nd October 2006 at 05:24 AM.

2nd October 2006, 08:51 PM	#10
HiTech	set the color all the way to minimum and note how the picture looks. B&W should look obviously proper. If not it may be screen drive adjustment, to weak crt gun issues. __________________ Don't make me reach through this monitor to slap you a good one!

2nd October 2006, 10:04 PM	#11
Hero999	Lol, I've still got to get around to doing this. I think I'll try the service menus first because I don't w3ant to risk messing it up when I open the case. __________________ I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong. Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.

3rd October 2006, 02:58 PM	#12
HiTech	you don't need the service menu to do what I mentioned. Simply turn the color setting to its minimum and note what the pic looks like in black & white. It should look true and no hints of R, G, or B tint to it. If B/W looks true then the crt isn't the culprit. __________________ Don't make me reach through this monitor to slap you a good one!

5th October 2006, 09:07 PM	#13
Hero999	I see what you mean now. I'll give it a go! __________________ I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong. Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.

8th October 2006, 01:43 AM	#14
Hero999	I turned the colour down to minimum and it still looked white, but there again there is some red present so it will still look white. I think it's probably the tube or an associated circuit since the menu screens are still in colour and the red appears to be very dark, the yellow looks slighty greenish and the magenta is violet. __________________ I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong. Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.

10th October 2006, 10:15 PM	#15
Hero999	Am I right then? Does anyone agree that tube is probably worn out? I'd like to be at least 90% sure nothing can be done before we dump it and buy a new one. __________________ I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong. Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.