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CRT Distortion lines on inputs, perhaps caused by temperature?
Posted by
aseriouslee
on 18 Mar, 2017 19:15
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I don't have extensive technical knowledge, so my apologies up front.
I have a JVC-HV32D40BK, and for some reason after about 10 minutes or so after being switched on, small distortion lines appear and slowly rotate around the screen in an anticlockwise fashion. When they're vertical, they appear quite thick but when completely horizontal they're so fine as to be almost invisible. After some time, perhaps an hour or so they completely dissapear until I switch the set off and on again.
They do not appear on the tv menus, so I know these lines must be interference from the inputs, and since they appear for a set time after being switched on, I believe they might have something to do with temperature.
Can anyone advise me as to how to rectify this problem without killing myself or the TV?
Thanks in advance.
EDIT: here is a picture of the lines against a grey background; the bar in the middle is just the screen's refresh rate.
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#1 Reply
Posted by
james_s
on 18 Mar, 2017 19:34
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Can you get a picture of the distortion? Doesn't sound familiar but it's difficult to visualize from the description.
Does it happen on all inputs?
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I have only tested it on the component and composite inputs, but both are affected. The input I'm using now is component.
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#3 Reply
Posted by
T3sl4co1l
on 18 Mar, 2017 21:08
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Bars rotating slowly are mains frequency (60/120Hz) ripple rotating with respect to 59.94Hz NTSC program.
Replace filter caps.
Tim
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Thanks, why do these rotations stop after a while though? if the same current is going in constantly, surely the problems would persist as long as power is coming from the same source?
also, what are the filter caps and how do I replace them?
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#5 Reply
Posted by
james_s
on 18 Mar, 2017 23:24
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Oh, a rolling bar, those are frequently called "hum bars". When you said rotating, I was thinking rotating around the other axis and that didn't make sense.
It could be a filter capacitor in the power supply, electrolytic capacitors tend to have higher ESR when cool and then improve as they warm up. A can of freeze spray could be very helpful to track this down. If you can't get free spray, those cans of air duster work if you hold them upside down.
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I think you might have mistaken the black bar in the middle for the distortion I mean. I'm referring to the jagged lines running across the screen like lightning.
Here's another picture to show you. Note how they're thicker here as they've moved more vertically in the anti-clockwise rotation.
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#8 Reply
Posted by
james_s
on 19 Mar, 2017 04:14
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500kHz is in the range that could be coming from a buck converter in another device. Have you tried a different video source?
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#9 Reply
Posted by
T3sl4co1l
on 19 Mar, 2017 11:31
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I think you might have mistaken the black bar in the middle for the distortion I mean. I'm referring to the jagged lines running across the screen like lightning.
Here's another picture to show you. Note how they're thicker here as they've moved more vertically in the anti-clockwise rotation.
That's not an image artifact, that's a camera artifact.
Or -- it
could be an image artifact, but we have no way of knowing that for sure. It's more commonly seen in pictures than in person, because cameras only read pixels, and their pixels don't line up with the display's pixels.
In any case, the word you're looking for is:
https://en.wikipedia.org/wiki/Moir%C3%A9_pattern 
Tim
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I assure you it's not a camera artefact, the distortion you see there is visible to the naked eye. I realise it's mixed in with a whole sea of other effects that come with capturing any screen on a camera, but those ones are very visible and annoying. For reference, here's my screen when I switched it on today before they set in, and after when it appeared a few minutes later.
I don't live particularly close to any radio towers, and no CRT's I have used before in this area had a problem like this. Plus, again the fact it comes and goes quite predictably implies there's nothing that could be constantly transmitting causing the interference.
Many thanks for your efforts so far in identifying what this effect is called, though I'm still not sure as to what's causing it.
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#11 Reply
Posted by
tkuhmone
on 19 Mar, 2017 17:54
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I remember also seen moire patterns on my old CRT monitor (446Xpro), maybe worth of checking if your display has adjustment menu for it. Could help a bit...
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#12 Reply
Posted by
T3sl4co1l
on 19 Mar, 2017 18:52
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Ahh, so it's definitely a thing, in person.
Does it change if you hit the degauss button (or select it from OSD options)?
You may have ambient magnetic fields messing up the beam path. Usually results in a much more noticeable rainbow effect, but Idunno.
Color convergence might also be a cause. The monitor probably has dynamic convergence (i.e., there's a beam-position-tweak signal, generated internally, that adjusts the beam as it scans across, mainly to account for the non-spherical shape of the screen), and if that's lagging for some reason, the picture will suffer.
Graphical Moire shouldn't appear for solid colors. It's normal for patterns, e.g. 50% gray, where the pixels won't quite line up with the pattern of phosphors on the screen (or the shadow mask / aperture grille).
There may be a Moire setting, though that may not be a good solution, either: AFAIK, the method used is shifting the entire display about a half pixel's distance, every frame. So the screen judders at half the refresh rate, like it's an interlaced display or something, except it's not. (The reason this can solve Moire: by shifting the screen half a pixel, the areas of pixels that were in the unlucky shadow areas pop out into view, while at the same time the areas that used to be bright, move into shadow; the average is hopefully a uniform picture. The flicker may be irritating, though.)
The pattern changing over time is interesting. Does it change quickly or slowly? If seconds to low minutes, it could be heating of electrical components, and something's out of spec and being sensitive. If slowly (mins to tens of mins), it could be thermal of something much bigger, like the CRT (and its aperture grille), or something that doesn't get hot by itself, but is heated by everything else getting hot, and doing the same thing.
Tim
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#13 Reply
Posted by
james_s
on 19 Mar, 2017 23:01
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Something else that might help, has this problem always been there or did it appear recently? Did it show up suddenly or gradually get worse? Did anything change in the setup? Any new electronics in the vicinity?
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I got the tv recently and it's had the problem the whole time. I don't think it's caused by temperature now as it comes back even when it's only been off around half a minute. I have tried removing all electronics near the set, so I don't think they are causing interference. Right now I do have a sound system plugged in under it, with speakers, but it seems that whether or not it's on or plugged in the moire effect persists.
There is no degauss setting I can find; with that said the screen doesn't have perfect geometry. It curves inwards slightly towards the bottom, so I'm considering getting a degaussing rod anyway to see if it will help. Do you think this could potentially solve the moire problems?
The pattern moves quite slowly, it definitely takes minutes to do a full circle though as it becomes more horizontal its harder to see, and so not easy to observe. There's no colour to it, more of a zebra effect with darker stripes.
The effect seems to be happening on the inputs; it doesn't happen on the OSMs, so I don't think its a problem occurring on the beam. There must be something happening between the signal being received and shot onto the screen. It can't be a problem with my cables or an individual input however, because I've used a PS2 with the composite input as well as my PC (through an HDMI-RGB) on the component. Both have the moire effect on the display, so I do think there's something occurring within the TV itself.
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#15 Reply
Posted by
james_s
on 21 Mar, 2017 21:33
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I don't think this is a degaussing thing, that is to fix purity errors, which are splotches of the wrong color. Geometry is never perfect on a CRT, and in many TV sets it was actually really poor, that is one advantage of flat panel displays.
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#16 Reply
Posted by
tkuhmone
on 21 Mar, 2017 22:44
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At least on my CRT monitor (446Xpro), degauss did not permanently solve moire problems. It only affect slightly - after it was applied. Moire never disappeared, and it was most visible in the neutral grey areas...
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I can see the Moire due the camera's pixels. I can also see
the pattern, its lines move about as the line-frequency and the interfering frequency drift about slightly, seen it loads of times!
What is the TV mode/line-frequency?
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I'm not sure what the tv mode / line frequency is. The component input is a 1080i signal at 60hz (which I think is also known as 1500i)
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I think 1080i is about 27kHz, never heard of 1500i !
While the pattern is slowly drifting around can you see any modulation in it, speech modulation is usually easily recognisable.
Sometimes another connected PAL or S-video video source can produce similar, even if the source is not selected.
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There is a very noticable "wiggle" effect on the screen, the lines are never still. The wiggle is fast, though the rotation is slow.
I don't currently have any other inputs besides component plugged in.
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The wiggle is fast, though the rotation is slow.
That sounds like it could be voice modulation to me, try listening to R4 and work your way up!
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I'm curious, how would modulations in sound lead to on screen effects? Also apologies, but what do you mean by "R4" and working my way up?
I haven't noticed any particular issues with sound in itself, though when quiet the TV speakers make an annoying "peep" noise when sound starts playing or ends.
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what do you mean by "R4" and working my way up?
I meant you could try listening to Radio 4 on 198kHz, to see if the modulation/fast wiggles match the sound, and then working your way up the MW band stations.
You could listen to the digital versions of them but there may be 2 or 3 seconds delay between what you see and hear.
It could be a SMPS, but it still looks like modulated RF to me, the waves look much too stable to be a SMPS.
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#24 Reply
Posted by
voltz
on 26 Mar, 2017 09:21
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Well i'm not really a TV engineer but we used to refer to this as 'herringbone patterning'. Well thats what we called it. It can be caused by a few things. Bad screening on the video cable was the most common problem or bad earth on the input jack to PCB. Have you tried other video sources? do they react the same?. Check the video lead screening is connected.
Sound modulation and PAL colour sub carriers can have an effect too if they are not properly nulled out in the receiver.
Sound (in the uk) is 6mhz and PAL colour 4.4333Mhz. These should be removed from the actual vision signal before being displayed. This is normally achieved using traps in the receiver to reject them, however if a miss alignment or drift in component value has taken place, these modulated carriers can become visible as herringbone patterning and other artifacts. They are not locked to anything being displayed so can appear to drift around and rotate. Sometimes visible, other times not.
But check video cable screening first and try another source.
Hope that helps.