Problem with red on a Panasonic TV.

[Hero999]

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]

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]

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]

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]

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

It's a TX-29AD2.

 

[Nigel Goodwin]

Here's how to access service mode.

 

[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.

 

[Nigel Goodwin]

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]

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,

 

[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.

 

[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.

 

[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.

 

[Hero999]

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

 

[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.

 

[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.

 

[StarBaseONE2]

I have worked on many TVs... I would say hundreds over the last 7 years.

Hi,

Sorry for your sets color problems.

Durring the time that I have worked on TVs, I have only seen THREE bad CRTs that had not been damaged... Shot in a rage, dropped from a table...etc.

I would still advise Checking into your sets Video Processor IC. If you can look up it's specs (There are several on-line sites to do this. I could send you a link), find it's R,G,B inputs and test the capacitors in their circuitry, either by substitution or with an ESR meter. This would probably see your set recover.

I say probably because I have seen open resistors, and shorted transistor color amps on the CRT board (actually on the neck of your CRT) cause this as well. Also it possible that the actual Video Processor IC has gone bad, although I doubt this as it took a while for your picture to deteriorate.

Good Luck.

 

[Nigel Goodwin]

Durring the time that I have worked on TVs, I have only seen THREE bad CRTs that had not been damaged... Shot in a rage, dropped from a table...etc.

Only THREE? - was that this week?.

 

[HiTech]

just wondering if the picture "blooms" when you turn up the contrast & brightness? Try it and if the picture starts to smear and lose good contrast ratio, then there's a chance of a CRT demise. Of course the proper thing is to test the CRT's emissions with a dedicated tester to assure it's not the "tube". There are other tv faults that can mimic a bad CRT.

 

[StarBaseONE2]

Mr Goodwin,

Surely you jest.

 

[Hero999]

just wondering if the picture "blooms" when you turn up the contrast & brightness? Try it and if the picture starts to smear and lose good contrast ratio, then there's a chance of a CRT demise. Of course the proper thing is to test the CRT's emissions with a dedicated tester to assure it's not the "tube". There are other tv faults that can mimic a bad CRT.

The red is dim and is also permanently bloomed, turning the brightness up only makes it worse.

I take it from what you're saying that the tube is probably damaged, is this true?