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PostPosted: Tue Sep 02, 2014 11:37 am 
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Black Belt
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Location: Havana, Cuba
I know that this post is probably more appropiate for an electronics forum, but I hope and trust that the electronics gurus of this forums can help me once again.

I have a 17" CRT monitor branded as Haier (el chapo, I think) tha was working fine, but from a few days on the image starts to shake horizontally (i think) so the monitor is almost imposible to be read, even the "NO SIGNAL" banner is shaking so I think it has to be something inside the monitor.

I´ve surfing the web and found a reference about something called ´X-mas tree effect´ but no other reference or explanation about how to solve it.

so I need any clue about how to solve this problem or at least where I can look inside the monitor or what component I must check

many thanks in advance

SAMH

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PostPosted: Tue Sep 02, 2014 3:35 pm 
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Mobo-fu Master
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A CRT monitor is very prone to EMF effects from nearby objects.. even power pole transformers, if less than 10 feet distant!
Any device with a power transformer in it within two feet can also give a CRT monitor the "shakes".
So too can low-frequency transmission towers if within 1/10th mile.. under 200 Hz.
Near a motorized device, like an air conditioner or refrigerator?
Even power mains with less than pure 60 Hz (or 50 HZ in some areas) can cause a CRT monitor to have problems with stability.
Try the monitor in different areas. Try a different refresh rate.. 70 HZ or 75 HZ instead of 60 HZ or 120 HZ. If the same problem everywhere, contact the sales outlet and have a talk.

There is a degaussing coil around the front edge of the monitor.. to clear any residual magnetism so the image is pure.
It should be on for only 5 seconds or less, when the set is turned on.. and a thermistor slowly shunts its power to the main circuit board. If that thermistor is bad, some power will always be applied to the coil. And result in a shaky image.

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PostPosted: Wed Sep 03, 2014 6:59 am 
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Black Belt
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Location: Havana, Cuba
I checked all the capacitors in the SMPS and nothing

the monitor is no close to any EM emitter it is disassembled on my reparations desk.

the image just moves continuosly from one side to the other of the screen, and the borders (left and rigth) are moving forming a pattern that resembles the leafs of a xmas tree

The PCB has the following numbers on it:

LK-29 94V-0 E78613

is there any choice of get an schematic or diagram of it??

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PostPosted: Wed Sep 03, 2014 7:45 am 
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Mobo-fu Master
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A manual or schematic may still be available..
http://www.tv-forums.com/forum/TV_Equip ... l_P128162/
http://www.theschematicman.com/
Some other sources, also.
A CRT TV and CRT monitor are nearly identical in all respects.. except a monitor has an external video input, and may not have the tuner feature.
The first description of your problem indicated the image may have been truly "shaky" as being influenced by external sources.
But if the image rolls sideways, that is a horizontal stability problem internally with the control circuits.
If the image rolls up or down, that is a vertical stability problem.
Or the input signal rate is beyond the monitor's limit, causing multiple images.
Capacitors don't need to exhibit physical signs they are bad.. that is the terminal phase. Internally, they can short and cause unwanted voltages to pass to other circuits. Or allow ripple effect on what should be pure DC voltages.
Capacitors used in computers and high-grade electronics normally are rated at 105°C temperature. For most other applications, they can be rated at 85°C. But in a CRT monitor, there is not a proper air flow sometimes.. and the temperature can go beyond the base rating of components. Capacitors can also dry out internally, without external signs.

Have you tried other refresh rates?
Refresh Rate Frequencies: (nominal)
Resolution.....Horizontal......Vertical
640x480........31.5 Khz..........60 Hz
800x600........48 Khz............72 Khz
1024x768......58 Khz............60 Khz
1280x1024 ....64 Khz............60 Khz
1280x1024 ....80 Khz............75 Khz

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PostPosted: Fri Sep 05, 2014 10:41 am 
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Black Belt
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there is a picture of the monitor so U can see the image

http://www.2shared.com/photo/vAwRYuYl/Haier17CRTr.html

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PostPosted: Fri Sep 05, 2014 4:01 pm 
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Mobo-fu Master
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"Tearing" along only one side of the screen, or both? Looks like the entire image is affected.
Have seen similar effects before.. due to a failed thermistor in the degaussing circuit. The coil is always partly energized.
A regular hiker's compass is a tester, would disclose any AC activity in the coil. The compass needle would vibrate back and forth rapidly! Heating around the front of the tube casing also would indicate the condition.
That thermistor is supposed to go almost zero resistance after about 3 seconds.. and all power shunted to the chassis. Some older sets used an inverse thermistor, which went near infinity on warming. Some designs use a separate control for soft energizing and turn off. The built-in coil is in a parallel plane with the shadow mask.. and does not give the same color "running" as when a degaussing coil is used externally.
Have heard of some instances where a diathermy machine or brush-type motor is on the same power circuit. That too can cause video artifacts.
The video signal cable can pick up external interference if not grounded properly between the monitor and computer. It is recommended that the same power outlet be used for a monitor, computer and printer setup. Using different outlets can cause a ground-loop effect. Very low voltage, but high current (a few amps, perhaps).

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PostPosted: Mon Sep 08, 2014 4:55 am 
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Black Belt
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Location: Havana, Cuba
thanks again karl, the effect is shown in both sides of the image, the picture I took wasn´t in the best angle, I´m sorry

I will check the degaussing circuit

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