Problem with red on a Panasonic TV. - Page 2 - Electronic Circuits Projects Diagrams Free

StarBaseONE2 · 11th October 2006, 03:53 AM

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** · 11th October 2006, 09:06 AM

Quote:

Originally Posted by StarBaseONE2

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 · 11th October 2006, 04:03 PM

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 · 11th October 2006, 06:58 PM

Mr Goodwin,

Surely you jest.

Hero999 · 11th October 2006, 07:04 PM

Quote:

Originally Posted by 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.

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?

**Nigel Goodwin** · 11th October 2006, 10:13 PM

Quote:

Originally Posted by StarBaseONE2

Mr Goodwin,

Surely you jest.

NO!, I've been repairing TV's professionally for 35 years, I've seen LOAD'S of duff tubes, certainly dozens per year. The current really cheap sets (mostly made in Turkey) have a VERY short tube life, and Philips tubes are well known for early failure, no matter what set they are in. I probably see at least one Sony Trinitron duff per month - but we are a major Sony dealer!.

tunedwolf · 12th October 2006, 12:25 AM

I would say Nigel is correct here...

Modern sets, certainly all that I have seen in the last 15+ years, have all used one scheme or another for automatic tube compensation. When the tube can no longer be controlled by automatic means, all sorts of poor picture troubles show up. Probably among the most common would be flaring of one gun or another, usually seen as streaks of colour around edges in the picture, but at the same time a lack of definition of that colour in the actual picture content as a whole.
Loads of fairly modern sets will actually blank the picture completely when the tube wears beyond automatic control. Philips sets seem to be very prone to this in my experience, or maybe I have just been unlucky...also most of the sets in recent years I have ran across using Philips tubes all seem to have had tube issues of some sort or another. About 5 years ago I had two that failed within warranty, the original factory fitted tube, and the replacement sent from the factory several months later, I chased the set to another dealer the last time to fight the warranty claim.

A common trick, to get a last gasp from a dud tube a good few years back, was to reduce the filament resistor in value a little, making the cathodes a little hotter, but to be honest, the mileage of doing that in a modern set is doubtful at best. I think your best bet is to rip out the chassis and donate it to your local repairman for spares, and scrap the cabinet and tube at the local amenity tip. It's unfortunate, but we now live in a throw away world, and the cost of a repair of this nature would be better spent on a new set.

penoy_balut · 12th October 2006, 12:35 AM

if you can check voltages on cathode drives (RGB) and they are good then tube could be defective

**Nigel Goodwin** · 12th October 2006, 09:12 AM

Quote:

Originally Posted by tunedwolf

Philips sets seem to be very prone to this in my experience, or maybe I have just been unlucky...also most of the sets in recent years I have ran across using Philips tubes all seem to have had tube issues of some sort or another.

As I mentioned earlier, Philips tubes have had MASSIVE reliability problems, many set manufacturers have extended the warranty on the tubes because they know it's a manufacturing defect and they don't have a leg to stand on in court!.

HiTech · 12th October 2006, 02:23 PM

Quote:

Originally Posted by Hero999

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?

Without using a CRT tester to confirm the condition of the CRT, I would now strongly suspect the problem to be the picture tube. Can you get ahold of a CRT tester or have someone test it for you? They should also be able to rejuvenate it as well. Rejuvenation does improve things for awhile... depending on how many hours daily the set is used it could last for months to a year or more to just several weeks.

Hero999 · 12th October 2006, 09:22 PM

Also as it's been deteriourating for awhile. . .

Anyway, I'd like to learn more an oscilloscope has a focus control, right? so do you think the red electron gun has just become badly out of focus? Perhapps the focussing circuit has gone wrong and it can be repaired. There again it might be electron sputter on the red cathode, this would certainly explain why it's deteriorated over time, in which case the tube is probably worn out.

**Nigel Goodwin** · 13th October 2006, 09:17 AM

Quote:

Originally Posted by Hero999

Also as it's been deteriourating for awhile. . .

Anyway, I'd like to learn more an oscilloscope has a focus control, right? so do you think the red electron gun has just become badly out of focus? Perhapps the focussing circuit has gone wrong and it can be repaired. There again it might be electron sputter on the red cathode, this would certainly explain why it's deteriorated over time, in which case the tube is probably worn out.

The focus is common to all three guns, generally what happens is one, or more, guns go 'low emission' - as suggested boosting the CRT might help short term, but modern tubes don't boost terribly well!.

Hero999 · 13th October 2006, 03:37 PM

What about the blooming on the red? I take it nothing can be done about this?

HiTech · 13th October 2006, 03:44 PM

The blooming is a result of the low emission. Just install a new CRT, or test & rejuvenate it, or dump the whole thing in the trash and buy a new set, make a sandwich, sit down & relax to a good movie.

Hero999 · 14th October 2006, 01:49 PM

I think we'll dump it and buy a new TV, since analogue TV is going to be turned off in a couple of years time so we'll need to go digital anyway.

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11th October 2006, 03:53 AM	#16
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. __________________ ...Located on the fringes of the Cosmic CoastLine... .....Deep, Deep, in the Engineering Section... .......StarBaseONE2

11th October 2006, 04:03 PM	#18
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. __________________ Don't make me reach through this monitor to slap you a good one!

11th October 2006, 06:58 PM	#19
StarBaseONE2	Mr Goodwin, Surely you jest. __________________ ...Located on the fringes of the Cosmic CoastLine... .....Deep, Deep, in the Engineering Section... .......StarBaseONE2

12th October 2006, 12:25 AM	#22
tunedwolf	I would say Nigel is correct here... Modern sets, certainly all that I have seen in the last 15+ years, have all used one scheme or another for automatic tube compensation. When the tube can no longer be controlled by automatic means, all sorts of poor picture troubles show up. Probably among the most common would be flaring of one gun or another, usually seen as streaks of colour around edges in the picture, but at the same time a lack of definition of that colour in the actual picture content as a whole. Loads of fairly modern sets will actually blank the picture completely when the tube wears beyond automatic control. Philips sets seem to be very prone to this in my experience, or maybe I have just been unlucky...also most of the sets in recent years I have ran across using Philips tubes all seem to have had tube issues of some sort or another. About 5 years ago I had two that failed within warranty, the original factory fitted tube, and the replacement sent from the factory several months later, I chased the set to another dealer the last time to fight the warranty claim. A common trick, to get a last gasp from a dud tube a good few years back, was to reduce the filament resistor in value a little, making the cathodes a little hotter, but to be honest, the mileage of doing that in a modern set is doubtful at best. I think your best bet is to rip out the chassis and donate it to your local repairman for spares, and scrap the cabinet and tube at the local amenity tip. It's unfortunate, but we now live in a throw away world, and the cost of a repair of this nature would be better spent on a new set.

12th October 2006, 12:35 AM	#23
penoy_balut	if you can check voltages on cathode drives (RGB) and they are good then tube could be defective

12th October 2006, 09:22 PM	#26
Hero999	Also as it's been deteriourating for awhile. . . Anyway, I'd like to learn more an oscilloscope has a focus control, right? so do you think the red electron gun has just become badly out of focus? Perhapps the focussing circuit has gone wrong and it can be repaired. There again it might be electron sputter on the red cathode, this would certainly explain why it's deteriorated over time, in which case the tube is probably worn out. __________________ 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.

13th October 2006, 03:37 PM	#28
Hero999	What about the blooming on the red? I take it nothing can be done about this? __________________ 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.

13th October 2006, 03:44 PM	#29
HiTech	The blooming is a result of the low emission. Just install a new CRT, or test & rejuvenate it, or dump the whole thing in the trash and buy a new set, make a sandwich, sit down & relax to a good movie. __________________ Don't make me reach through this monitor to slap you a good one!

14th October 2006, 01:49 PM	#30
Hero999	I think we'll dump it and buy a new TV, since analogue TV is going to be turned off in a couple of years time so we'll need to go digital anyway. __________________ 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.