Do We Need to Replace the TV?

Factual Questions
1

Well, like everybody else at the moment, we’re spending a lot of time glued to the television. (Hey, if I can’t go back to work, I might as well watch them clear out the streets by the office.) And a recurring picture problem we’ve been having seems to have suddenly become permanent.

The Problem: We hear a sudden ‘click!’ from the TV and the color of the picture goes all crazy. There will be a wide stripe in which everything has a blue-green tint, next to a wide stripe in which everything is purple, next to a yellowish one… The stripes are broad arcs, sort of a rainbow pattern, although they don’t form perfect semicircles.

How We’d Been Solving It Up 'Till Now: The ever-popular ‘give it a good whack.’ A thump with a fist (or two, or five) on the top of the screen would fix it. This no longer works.

What’s going on? Can it be repaired, or would it be more cost-effective to give up hope and move on?

Comments on whether or not we should replace the television, rather than just doing without, should be referred to Great Debates.

2

IANA repair technician, but I have been through a fair number of TV sets in my time.

Generally speaking, if it’s 19" portable or smaller, it’s just not cost-effective to ask someone to repair it. It’s going to be cheaper, easier, and faster to buy a new one.

[insert your choice of sermons about “today’s throwaway society”]

There are a number of TV Repair FAQs out there on Google.

http://www.google.com

3

Sadly, IANA repair technician either. And the FAQs I have found thus far have all been written with the technician in mind. That’s why I’m here. I am continuing to dig for other sources, of course, but I thought somebody out there might have a top-of-the-head explanation.

4

Actually, I am a tech. It sounds like you have one of two problems: a faulty degauss circuit, or a detached shadow mask.

Background: Inside the CRT is a metal screen with a lot of little tiny holes in it. This is the shadow mask, and it plays a role in getting the beam to the phosphor spots it needs to hit on the glass. Sometimes the mask becomes magnetized and deflects the beam to places it shouldn’t go, resulting in color distortions on the screen. This is common enough (in fact, just moving the set around causes this) that every TV includes a degauss circuit that demagnetizes the mask by pulsing an electromagnet wrapped around the front of the CRT when the set it turned on–this is what causes that <click-BZZzzzmmmm> sound that you get when you turn the set on.

If you hear that sound following the click you mentioned, then it’s probably your degaussing circuit coming on when it shouldn’t (they’re designed to only run at cold-start of the set). This isn’t really likely, as the circuits are really simple, and there isn’t much to go wrong with them. If this is the problem, then it may be as simple as a loose plug–it was only connecting intermittently, and bashing it made it connect again until you jarred it all the way loose.

Otherwise, the shadow mask has probably become detached (or severely warped)–this sounds more likely, given that bashing it had an effect. The only fix for this is replacing the CRT, which is very expensive. You should almost certainly replace the set in this case.

If it’s 25" or larger, I would suggest finding a shop with a low estimate fee to check the degaussing. Otherwise, you should probably just get a new one.

5

Which answers something I’ve always wondered about: why does the TV set make a noise when I plug it in, even when it’s off? That must be the “cold start” you’re talking about. Modern TVs, as I understand, are designed to have that standby feature so that they don’t have to warm up like sets from Ye Olden Dayes.

6

Thank you Balance mate!

You’ve answered a question of mine too. I’ve had these two little fuzzy corners of my TV that don’t have the right colours in them. Red looks green when it hits that part of the screen.

I felt that there was nothing I could do, and now I know that I can’t, but at least I can tell people it’s the detached shadow mask, and that I can’t afford the de-gaussing.

What’s that?

Oh, um, since I well, sort of dropped the TV set upside down. While carrying it into the bedroom, with a bottle of drink and a plate in my other hand.

Yes, I know.

Redgauss.

7

You may well have warped the mask, Red. On the other hand, screwy as it sounds, an impact can cause the mask to become locally magnetized. In the latter case, it will probably go away on its own eventually. Or you could get a circular electromagnet about 10 inches across and run it around the screen in a gentle circular motion (about 4 inches away), then center the magnet in front of the screen and back away until the colors go back to normal. It’s a cool process to look at, but I can’t guarantee results–it could just make it worse. Don’t wear an analog watch while you’re doing it; it makes some of them go completely nuts, and go forward or backwards an hour every minute or so.

Oh yeah, make sure you don’t have any speakers sitting near the set–the magnets in them can foul up the colors, too, especially if the degauss circuit isn’t quite up to snuff.

Grumpy, the standby feature involves the preheating of the cathode (the plate that emits the electrons for the beam–CRT=cathode ray tube) so that it’s ready to start pumping out the electron beam on demand–old sets didn’t start heating it until you turned the set on. The preheating is silent unless there’s a problem. The degauss circuit is often connected directly to the AC line input via a thermistor (a resistor that becomes more resistive to electric current as it gets warmer, like you’re closing a valve). When the resistor gets warm enough (in less than a second), it chokes off the current to the magnet, and the degaussing stops. The sound you’ve noticed is the current humming in the coil, combined with a buzz from the shadow mask being shaken by the oscillating magnetic field.

Next Week: Chopper Power Supplies 101 :smiley:

8

Giving it a hit usually means a loose solder joint but I use that idea for computer monitors.

One guy got something like that because his phone was too near the tv & got interference.

Best thing to do is unplug tv from wall for a minute or so & plug back in, this resets the electronics.

How old is this thing?

9

I recently heard some guidlines regarding when electronic equipment is no longer cost effective to fix:

Computer - 5 years
TV - 3 years
Printer - 2 years

Anything thing older than this should be replaced rather than fixed. I bought a new HP printer yesterday to replace my previous (4-year-old) HP.

10

Those figures are pretty reasonable for computers and printers (if anything, I would give the computers a shorter span). With TVs, though, it depends on the set; some of the smaller, cheaper sets aren’t worth fixing immediately after the warranty ends (generally 90 days or 1 year). Others, like a Mitsubishi 35" or 40" direct-view are probably worth fixing until the CRT starts to fade (around 7 years in most cases), unless it happens to be a CRT failure.

That said, I have repaired sets that were 20 years old at the time (you should have seen those things–they predated the use of PC boards in consumer electronics, so they were jumbles of wires with components soldered to metal posts). I thought the owners were fools, but I repaired the sets.

11

You’re right. I had forgotten that the 3 years is for a 19" TV.

12

I think I got it. Channels 4,7,9,11, and 13 (NYC) getting knocked out by the crashes…the round the clock coverage on CNN and CNNfn watched by 50 million around the world saving the two cable stations…you can only get those above-mentioned channels on cable…the last few weeks the front pages and TV news stories were all about Mariah Carey and other fluff, stuff that nobody wants to watch or read…it all comes together. The terrorists are in cahoots with Time Warner and Cablevision to force the last few holdout customers to pay $79/month for cable, and to increase dwindling ratings for the flagship news channels. How’s that for a conspiracy theory?

13

Now that this thread appears to be done, I’d like to hijack it, specifically to pick Balance’s brain.

Firstus: When I bring a magnet near a CRT screen, is the color distortion due to the shadow mask warping, or the magnetic field deflecting the electrons? Either way, why is the distortion a uniform color? Seems like it would vary by distance from the magnet, and possibly by whether it’s to the left or right of the magnet, going by what little I know of CRTs.

Secondus: We have a TV, probably about 8 years old, that brings cable channels in just fine. One local station comes in perfectly. Another station comes in fine sometimes, but sometimes, when tuned to that station, the screen will suddenly have alternating bands of distortion (that’s the best I can describe it), and a loud buzzing will come from the speakers. Usually it’s still possible to hear the audio and make out the picture. I noticed yesterday that the audio distortion got worse proportional to the amount of white displayed on the screen. So that’s that channel. The other 3 or 4 local channels come in … well, like you’d expect on an old TV. Faint double images, a broad vertical band on one side of the screen… actually, I haven’t watched anything on those stations in a while, because it’s so annoying to me, so I can’t describe the problems any more accurately than that.

Secondus (part b): do local signals come in over the cable line? My WAG is that they don’t, and we’ve got a problem with our tuner on the lower channels (the channel that comes in clearly is 24, the sometimes-channel is 18, and the bad ones are 12, 6 and 4). If both signals are coming in over the cable line, then I’m stumped.

Possibly pertinent info: The cable goes into the “IN FROM ANT” coax plug on the VCR, and the out plug on the VCR is plugged into the TV antenna plug. There’s also three RCA plugs going from the VCR to the TV, one for video and two for audio. Also, before we had cable, channel 24 came in fine, 18 was a little fuzzy (but didn’t have the intermittent problem described above), and the other channels were about the same as they are now.

Thanks for any help or info you can give.

14

GrandfatherTrout, look at the back of the set, youll see the date of manf of your tv, what is it? Who made the tv? There are a lot of tvs.

You can ttry unplugging from wall for a minute & plug it back in this resets things but Id rather know what the date of the set is.