Wrong colour on TV

[TBaba]

My TV just started acting up. It shows more of a yellow color generally. Sometimes when switched off themn on again, the colour is ok but then after an undefined time it goes back to a yellowish colour. does it need blowing/dusting or what? any assistance is appreciated . i am technicaly inclined so i can understand some technical work . thanks!

 

[IRstuff]

Have you tried degaussing it?

Are there magnetic fields near the set?

How old is the set?

Has anything changed on or near the set recently?

TTFN

 

[Skogsgurra]

Sounds like a "Gauss" problem. The Eart's magnetic field (or any other magnetic field) influences the shadow mask so that you get miscolorations. There is a degaussing coil in the set and this coil produces an AC field with decaying amplitude that degausses (takes the magnetism away) each time the set is switched on (you can often hear the "thump" sound from the current surge).

The degaussing usually needs a few minutes to recover after first turn on, so it will not work if you switch off/on in a rapid sequence.

Why your set is sensitive is difficult to say. Do you have any large DC circuits close to the set? Or any big magnets? It can be anything, really. Like supply wires to a galvanic bath, a train or tramway, certain lab equipment and so on.

Try moving your TV to another place and see if things change. Warning: Do not believe people saying things about Earth Radiation, Hartmann lines or Curry crossings. That is complete rubbish.

Gunnar Englund

http://www.gke.org

 

[IRstuff]

Could simply be that the degaussing function is kaput.

TTFN

 

[ScottyUK]

Blue gun on its way out? Or drive signal to same?





----------------------------------

If we learn from our mistakes,
I'm getting a great education!

 

[itsmoked]

Except he sez it's fine right after turn on.. So deguassing is working... Then the problem creeps in.

I too think you have a magnetic field near by.. New speakers? Air cleaner? Record player? Fan? Air conditioner? Battery charger? Fluorescent light? What have I missed?

Could also be a componet shifting value with warmup... If the set is filling with dust something could be overheating.

 

[SolderingGunslinger]

Hmmm...one time, you spell color the way we Yanks do, then you spell colour the way the Brits (and former colonials in many parts of the world) would.

Are you, perhaps Canadian?

There have been indications that the earth's magnetic field is becoming unsettled and will switch polarities sometime in the near (geologically speaking) future.

Are you sure the North magnetic pole isn't drifting under your set?

From someone who has fixed more than his share of TV sets (I started when I was eight years old), I would start by gently blowing the dust and other crud out of the set. If the problem creeps up on you, I would suspect a heat related problem. Fire up the set with the back off and wait to see if the problem crops up. If it doesn't, replace the back, but don't screw it down. See if it comes back once again. If not, your cleaning job probably fixed it.

If the problem comes back, get a can of freeze mist and chill carerfully chill aome components in the CRT drive sections if you chill one component and the problem diasppears, replace that component.

If you have a service manual for that particular chassis, a good VOM and an oscilloscope, you can troubleshoot the set in that way as well, however if you have the proper tools, I shouldn't need to tell you how to do it.

If your set is PAL or SECAM, ask again and perhaps someone from the UK or the EU can come back with an answer.

Oh yeah, don't forget to charge yourself $50.00 for the service call and throw in a free degaussing of the CRT. :-D

I remain,

The Old Soldering Gunslinger

 

[MacGyverS2000]

I'm gonna go with Scotty on this one... suspect a component directly tied to the blue gun. I can't count the number of cheapie monitors that have gone that route (really wierd part is, and I have no relevant conclusion, the blue gun is usually the one to go flakey first).

Slinger has the right way to approach the test/fix method. With some patience, you shoudl be able to track it down. If you have a service manual, poke around at the right test points while the thing is yellow... you should find any errant testpoints that way.

Put a mirror in front of the tube so you can sit behind the monitor and see what's on the screen at the same time.


Dan
Owner

http://www.Hi-TecDesigns.com

 

[itsmoked]

If it is a problem with a component, {spelled correctly this time } The most likely are the dang pots!! The color adjust pot for the guns would be the first place I'd check. I have had more than two dozen pots fail on me.

 

[walker1]

Blue gun, or rather driving circuit, it sounds like.
That would be here in the EU and (I think) for you NTSC guys as well

I have seen quite a few circuits go bad after a warm-up.
Turned out to be bad/old soldering.
Some of those seem to turn into some sort of semiconductor, when the solder turns crystaline or something.
Of course, a warm-up can also change the mechanics in a circuit, so stress pulls a pin slightly off-contact. (bad/old soldering again)

 

[ScottyUK]

MacGyver,

I'm glad you made the 'blue gun dies first' observation. It happens to our DCS monitors which are in service 24/7/365 and it is almost always the blue one which goes first. I too have no explanation.

ItSmoked's probably on to something with pots and trimmers. The other chief suspects are connectors and wound components. The latter are heavy and thus prone to causing mechanical failure of the soldered joints if vibration or impact is or has been present at some point. This would tie up with a thermal expansion cause of failure after power on. Tricky to find. Tin/lead solder joints tend to develop a dull halo around a pin with the bad joint which shows up well against the shiny solder on the pad. Try gently tapping the board with a heavily insulated screwdriver or a tufnol rod.


----------------------------------

If we learn from our mistakes,
I'm getting a great education!

 

[johnwm]

I believe that the blue electrons get tired quicker than the green and red ones

Seriously though, if the change in colour is localised then it probably needs degaussing, but if the colour change is constant over the whole screen then it's in the blue drive circuitry. If it comes and goes then try for dry joints (tap with plastic knitting needle) or dodgy pot (wind up and down a few times)

Good Luck
johnwm
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[Cappels]

Your blue channel is intermittent. Its not degaussing or the blue gun (unless its an electrical connection to the blue cathode).

The following assumes that your television receiver is a Cathode Ray Tube receiver, not a flat panel receiver. If its a flat panel receiver, the odds are that you won't be able to locate the problem yourself, and even if you did, you would not have the means of repairing it. Take note: If it is a plasma televison, the panel driving voltages are painful and dangerous. If its a CRT television, the voltages are much more painful and can be leathal.

Most likely its a potentiometer, a connector, or a soler joint or crimp connection. These things happen.

If you are the brave sort of guy and have adequate knowlege of safety around high voltage (25 kv to 30 kv is common, then take of the back and install a cheater cord. If you don't know what a cheater cord is, STOP AND TAKE THE SET INTO A REPAIR SHOP, its for your own safety. Tap around the chassis -tapping the wires, connectors, circuit boards, etc. with an insulated tool -like a nonconductive plastic rod or long plastic screwdriver. Avoid contact with the CRT's anode cap, by the way, if the set is old, it may have cracks in the insulation. You might be able to identify a spot that, when tapped, makes the blue signal go and come (flashing the tube face between the "normal" colors and the yellowish colers. Once you find the most sensitive spot, look in that area for an intermittent connection or a noisey trimpot.

Keep in mind that the intermittent contact can also be a connection inside a component, in which case, you might not be abl to locate it or repair it yourself.

If in doubt, take it into the shop or buy a new one.

AND KEEP ON HAND IN YOUR BACK POCKET -SERIOUSLY.

 

[itsmoked]

AND KEEP *one* HAND IN YOUR BACK POCKET, SERIOUSLY!

And never do TV repair on a conductive bench.

 

[ftr11]

I do not know guys. Most tv sets and monitors work
10 and more years. And if tube was made by japanise or
close to them the tube is still ok. I would inspect
that small funny loking board attached to the tube
especialy trace of circuit board and solder joints.
Because TV operates at high tempreture and it cause
solder or traces to brake. On solder it will look like
tiny circle.

 

[TBaba]

I love this forum. so many replies.. you guys are so helpful. To answer Gunslinger Q., I'm actually nigerian but grew up in America. It's a Sharp CRT TV and has been in use for better part of 7 years. I'll attempt opening it and blowing then i'll poke around with a plastic material as most of you have advised. I'll post results. Thanks sooooo much!!

 

[walker1]

Careful there!

By blowing dust and filth away from one place, it may end up places you certainly do not want it.
This includes your lungs!