TV repair question

Last night we turned on our TV and the picture was wierd. Skin tones were blue, and the display digits which were previously green, were now red. Halfway down each of the sides there were semi-circular areas tinted green, and in the bottom corners semi-circles tinted red.
The set is a 29" Sony Trinitron, abotu 10 years old.
Ms. D called a TV repairman, who said it sounded like it needed “de-Gaussing” or something sounding like that. Said it was a relatively simple, and cheap repair, but nothing we could do ourselves.
Anyone familiar with TVs who can tell me whether this is a complete line of BS, how much such a repair should cost, how long it should last, etc?

Just behind the glass screen you see from the outside, there is another metal screen with lots of tiny holes or in the case of Sony trinitron tubes they are minute slots.

This is called the shadowmask.

The shadowmask allows electrons from each gun to strike the correct colour phosphor.

The problem is that electrons are fairly easily diverted by magnetic fields, which is why you should keep your louspeakers away from a colour monitor or tv unless those speakers have been shielded to allow this use.

If the shadowmask becomes magnetised it changes the path of the electrons such that they hit the wrong colour phosphors, resulting in colour corruption.

TV sets have a built in de-gausser circuit which operates when it is turned on or off, and this sends current through coils of wire around the outside of the tube, which in turn produces a magnetic field which “erases” any other magnetic field on the shadowmask.

If this circuit fails then slowly but surely colour purity will be compromised.

De-gaussing is not a big job, you don’t even need to take the back off the tv set, but if the de-gaussing circuit has failed then this will need repair.

Before you do this first make sure there are no electrical appliances nearby that can can produce a strong magnetic field nearby, things like loudspeakers especially though some other electrical appliances can be as guilty.

If the latter is the case then all you need do is remove said appliances and turn the tv on and off a few times, don’t do it like you were tapping out morse code, and it may well clear.

By turning off the tv set I mean completely and not just setting it to standby mode.

Sometimes, though usually rarely the shadowmask itself can become distorted, bent out of shape, by someone bringing a strong magnet close to it, and this damage can be permanent.

Have to add though that there are other things it could be, is the picture still geometrically accurate, especially around the middle edges ?

There are a couple of other possibilities from the alignement of the magnets on the neck of the tube to the convergence circuits maybe at fault.

De-gaussing is the first thing to look at, since its cheap and easy, but it may not end there(probably won’t)

The tech that does the de gaussing will probably check first but make sure you remove any magnetic tapes from the area or face losing them.
DeGaussing is a simple matter so it shouldn’t cost more than just the service call but the automatic circuit must have failed.Even so the circuit is simple and repair should be reletively cheap.The repair should last the life of the set.
Something caused the magnetism so you should look at the circumstances preceeding the problem. Like casdave mentioned speakers shouldn’t be placed near the set. Also avoid turning on electrical appliances like your vacuum near the set.

Thanks for the info. Just wanted to make sure the tech wasn’t giving me a complete line of BS, just making something up.

We turned it on and off a couple of times, but not several. I loaded it in the car, and my understanding is that the missus would drive it to a local shop today.
The picture was not distorted in any way (tho I do not understand what you mean by “the middle edges.”)

We do not have a stereo hooked up to or near this set. Only appliances in the cabinet are a VCR and a tape rewinder. It worked fine Sun morning, I vaccuumed the room Sun aft, and it did not work when next turned on Mon eve. But I have vaccuumed that room the same way for the last 5 years…

Any ideas how long a TV like this should last?

Any ideas how long a TV like this should last?
end quote

The picture has already degraded some you just don’t notice it.If you’d put a new set next to this one you would see the difference.
10 years is a long time for a set to operate IMHO.

By middle edges casdave is referring to pincushioning.Thats kinda self explanitory.

If I remember correctly, and this is a helluva lot of remembering, but the vacuum is the worst offender of magnetization. And it’s a cumulative occurance. Back in the early 80’s, we used a de-gaussing ring for this problem, I’ve not opened a TV in 15 years, so I don’t know if that’s still current, but I agree, that something else is amok in the system. Sony makes a fine product, I’m a devout buyer, but TV’s are so cheap these days, coupled with the fact that everything’s going to HDTV, ya might just look into blowing a wad on a new set, and not in the porno-movie kind of way…

ah, my answer is the same, unplug it or any other appliance from wall for a full minute. this resets them.

Looks like you did that when you
put it in your car & when he looked at it, the picture was fine.

When you do this with a tv it degausses it too, I believe.

In this age of throw-away appliances that are cheaper to replace than to fix, I’m surprised that people are still in the business of repairing TVs.

Well, 50 later, and the set is all the better for having been turned off, unplugged, and taken for a drive. Just doing my best to pump into the local economy.

I’ve learned more about TV’s in the three minutes it took me to read this thread than I have in my entire life.

One or more questiona remains for me: When my 18 month old son finds the remote control that I should have hidden better, and he powers my TV off inn the middle of a touchdown drive, SHOULD I wait 15-30 seconds before turning it back on?

What if I don’t (or he keeps pushing the on/off button?)
(It’s a 35" Toshiba, 'bout 4 years old)
And, since I just purchased a 60" Mitsubishi projection TV, can someone offer advice not usually given by the manufacturer? Like, this whole magentic thing and degaussing…this is the first I’ve seen of anyone making recommendations about speaker placement and such.


So the repairman didn’t fix it???
I’ll bet it does it again.
When you turn on the set do you hear that humm that lasts a few seconds???
That is the degaussing circuit working.
It is only a coil of wire wrapped around the pix tube near the front. It is ,or was, controlled by an electronic device called a thermistor. Like the name indicates it is a heat operated device. Every time you turn on the set it degausses the tv.
Keep your receipt.

Well, I do work for a TV manufacturing company. But DeGuassing is for TVs with picture tubes. A projection TV doesn’t need to be DeGuassed.

I prefer if people have questions they give the model number & the date of manf of the tv, its printed right on the back of the set.

But not because it doesn’t have picture tubes. Almost all projection TVs have 3 tubes (there are a few new models that use LCD or DLP, but you’d probably know if you had one - you’d have spent a lot more on it, for one thing). The difference is that the tubes don’t have shadow masks or aperture grilles, so there’s nothing to degauss.

Speaker placement is usually not a big concern with projection sets, for a couple of reasons:

  1. there’s no shadow mask, so the only (minor) risk would be for the magnets to interfere with the electron guns in the tubes

  2. Since the tubes are located in the center bottom of the set, your speakers would generally be placed far enough away due to the cabinet size.

The manufacturer has probably already recommended not to use video games with the set. That’s because video games tend to have bright non-moving images that can get burned into the tubes over time (that was the original reason that screen saver programs were developed for PCs). The same common-sense advice can be used for any image. Don’t leave the same image on the set for a long time. If you’re pausing a DVD for an hour, shut the set off.

Also, the tubes will last longer if you run them with lower brightness and contrast settings (and the picture will look more natural). Invest in a dimmer for your TV room and turn the lights down rather than turning the brightness up. Consider using a lamp rather than lighting the entire room.

When sets are shipped from the manufacturer they tend to boost the contrast and brightness settings so the sets will stand out in a showroom. Turn them down!

If you have a DVD player, invest in a copy of video essentials, which will help you make these adjustments and more.

And Handy, I haven’t yet seen any questions where the answer required knowledge of the specific model of set. This isn’t

If it’s just turned off once, turning it right back on shouldn’t be a problem. If you turn it on and off repeatedly you run the risk of heating up the degaussing coils, which aren’t meant for continuous operation, and could damage them or the set. This is unlikely; however, repeatedly turning the set on and off will cause undue wear on many parts and could shorten its life.

Well, he said he did and the set worked fine last night (Buffy, ya’know), but my wife didn’t sit around and watch him work on it. I was just joking about the folk who were suggesting that turning it off for a while was all it needed.

So now that I’m afraid to vaccuum the room, you think you’re gonna get me to put my ear next to the set to listen for a buzz when it turns on? Anything else? Should I paint myself blue and shove a marshmallow up my butt first?

Sometimes I prefer blissful ignorance. Dadburn newfangled technology (grumble grumble).

Just don’t turn on the vacuum in front of the tv

Well anything that trips your trigger
I can hear my PC monitor degauss when I turn it on. And My wife says I’m hard of hearing.

How close would you consider too close. Room in question has hardwood floors, with approx 3’ between front of TV to nearest edge of rug.