Alright, who's good at fixing TVs?

I picked up this Philips colour CCTV video monitor for really cheap, and, as expected, it's got a slight problem. The picture appears fuzzy in parts. Not grain, but it's got a horizontal zig-zag distortion going across the screen. The distortion isn't consistent throughout... there are some bands of clear picture, mainly towards the center of the screen. Adjusting the brightness/contrast makes the distortion change - making it brighter makes considerably more distortion, and it seems to be less distorted when darker (but far from perfect).

Picture:
**broken link removed**

It's a Philips LTC2910 9" colour CCTV monitor. PAL, 50Hz, 240V. (using it as a poor-man's video editing reference monitor)
PDF information sheet here: **broken link removed**

I've tried connecting it to a few different sources and it produces the same results.

The seller said "it's something to do with the high-voltage power converter, but be careful fixing it"... doesn't help me much.

If it's something reasonably cheap, I wouldn't mind fixing it... I don't have much knowledge or experience, though.

Help?

Thanks in advance

Looks like the green is overgunning, check the RGB guns on the neck of the tube.......... Or it may just need decausing (demagnitising).....

Please excuse my ignorance, but how exactly do I 'check' the guns? Where are they located, and what should I do to avoid killing myself?

And how do I degauss it?

You degauss a screen using a degaussing wand, or some monitors actually have a seperate degauss feature which you can initiate whenever you want. This is to cure problems where a strong magnetic field has been placed close to the CRT and produced purity errors, or if the monitor has been moved while it was switched on. You'd know all about it if you had purity errors - the whole screen would be a mix of deep purples and greens.
Regarding the overgunning thing, I don't think that's your problem. It looks from the picture as if you might have too much green in it, but I think it's just the way the picture has come out. Either way you definately have a problem seperate to that with the distortion in the picture, so concentrate on that first.

Distortion like that you describe can be caused by a problem in the switch mode power supply, or perhaps in the line output stage. I've not had many of these types of problems, but normally it's to do with a capacitor which isn't behaving itself anymore. It's not the type of problem that a novice to TV repair can really attempt, unless the component in question is waving it's hand in the air shouting "look at me, I'm faulty." Capacitors can sometimes give you this indication; they'll either bulge at the top or weep at the bottom, leaving a mess of toxic chemicals in their general area on the board. You could try taking the cover off and giving the board a really good visual inspection for these kinds of things.

BE CAREFUL because even when the TV is off, there are potentially dangerous high voltage areas on the board.

Brian

Thanks for the detailed reply. I agree, it doesn't seem like something a degauss would fix - I'm familiar with the discolouration from magnets, and it doesn't show any of this. The colour is fine, it's just the photograph that's a little off, which cancels out the 'guns', right?

ThermalRunaway said:

Capacitors can sometimes give you this indication; they'll either bulge at the top or weep at the bottom, leaving a mess of toxic chemicals in their general area on the board. You could try taking the cover off and giving the board a really good visual inspection for these kinds of things.

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I'll try that tonight to see if there's anything obvious

What should I do to avoid electric hazard? I know with computer PSUs you have to turn them off, disconnect and let them sit for a few hours to de-charge before opening them... Any kind of similar safety procedure for TVs?

The procedeure is exactly the same, since a TV has a switch mode power supply as well. Unfortunately though, it's not quite as simple as leaving it switched off for a bit and hoping for the best. The capacitors can stay charged for quite some time - more so under certain fault conditions. If you're really that new to this stuff I wouldn't recommend you take the cover off at all, but since you'll probably ignore me and do it anyway ;-) just take care not to touch anything. If you don't know what to touch and what not to touch, the best rule is don't touch anything!

Use a plastic ended tool to do the poking for you, and make sure the end isn't metal or you could end up shorting things out on the board. Just see if you can take a general look at the condition of the caps, or anything else that might be obvious. Sometimes monitors are encased in metal shielding and stuff. If you take the cover off and see lots of that, you'd probably be better off sticking the cover back on and leaving it to someone who knows TVs.

Brian

I am going to jump on in here with my TV problem.

I gave up trying to diagnose my tv so i sent it to a tv repair shop. They have come back and said its the transformer and it will cost me £75 to get it repaired. The Tv only cost me £200 when i bought it new 5 years ago.

Thing is i am not sure whether i am being ripped off here. Does a faulty transformer sound like it would have the effect i am about to describe.

Its a goodmans 28" CRT tv.

There is no picture when switched on screen is completely black. However the sound is working and can hear it clearly. when the Tv is switched on there is no high pitched squeek on start up that is usually familiar. (if you know what i mean).

A thank you to nigel by the way for his help but i had insuffcient skills to diagnose the tv any further. I was measuring voltages etc but just didnt know what i was looking for.

Andy

andy257 said:

I am going to jump on in here with my TV problem.

I gave up trying to diagnose my tv so i sent it to a tv repair shop. They have come back and said its the transformer and it will cost me £75 to get it repaired. The Tv only cost me £200 when i bought it new 5 years ago.

Thing is i am not sure whether i am being ripped off here. Does a faulty transformer sound like it would have the effect i am about to describe.

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It could well be the transformer (LOPTX), it's a common fault on TV's, particularly cheap ones like a Goodmans (which is just a name put on cheap bought-in sets, Goodmans have never actually made TV's). Even worse, Comet have the rights to use the Goodmans name on their cheap sets as well, so there are two completely different 'Goodmans' in the UK, both just badges on cheap imports.

If it is the LOPTX, £75 sounds a pretty decent price!.

Thank you nigel. I am glad you said that becasue i was thinking that is an expensive repair for a tv that is not worth really that much.

Thanks again

Andy

andy257 said:

Thank you nigel. I am glad you said that becasue i was thinking that is an expensive repair for a tv that is not worth really that much.

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That's the problem with cheap sets, generally repairs are no cheaper for a cheap set than an expensive one (and are sometimes more expensive!).

While £75 would only be 10% if your set had cost £750, as the set only cost £200 then it's 37.5% of the original cost. A 5 year old Goodmans probably wouldn't even be worth £75 in good working order?.

We rent TV's as well as sell them, I wouldn't automatically fit a new transformer in a 5 year old rental TV - we'd have to give considerable thought to it. Not that we wouldn't be happy to return the set for £75 and keep collecting rental?, but often you find that they ask for a replacement set a few months down the line. The set then comes back in, having had £75 spent on it, and you can't do much with it.

That's the trouble with TV repair these days, it's just not worth anything anymore. a 28" TV used to cost a grand, in which case a repair involving a £75 part would be more than reasonable. Now things are so cheap that even simple repairs aren't worth doing because there's not even enough money in it to pay for your time!

Electronics is the only trade where the value of things actually goes down. In every other trade, the value goes up with inflation. I think it's really sad that Electronics has to be treated so differently, considering the genius behind the design that makes these products possible.

Brian

Hah Nigel - I think we were both writing our replies at the same time!

ThermalRunaway said:

Hah Nigel - I think we were both writing our replies at the same time!

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I was two minutes faster