Question about LG Flatron F700B 17" CRT Monitor

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LG F700B Lines at top of screen

When first powering up the monitor when cold, I get a series of horizontal lines in the top 2 inches or so of the screen.
The picture at the very top of the screen appears to be slightly "Folded Over".
After warming up for around 10-15 mins the problem seems to correct itself.
I am assuming a cap is drying out, the problem is-which one?
I don't have a schematic, but if someone could give me an idea of where to look, I'm sure i could replace the component and save myself a nice little repair bill.
The monitor is around 6-7yrs old.


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i have same problem (exactly same!!)
see here i hope it is usefull
if it solve your proble please notify me

Posted on Jul 27, 2009

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I would check the video card , then the connector and if the lines are still there , then you need to replace the monitor

Jul 26, 2009 | LG Flatron F700B 17" CRT Monitor

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LG f700b raster problem

If the lines are slanted, you are seeing 'retrace' of the horizontal sweep. The distortion at the top is probably caused by a failing electrolytic capacitor in the vertical deflection circuit or in the power supply filtering for that circuit.
If you want to try to find this problem on your own, use great caution! There are exposed parts that can carry very nasty if not fatal voltages.
Go to any electronics parts source and buy two cans of 'freeze spray.' Expect to pay $4-5 dollars each for them. Using this on a 'live' monitor makes it still a little more hazardous since the cooled parts will form frost that may be conductive and I recommend keeping one hand behind your back so even if you touch something 'hot' you won't have currents passing through your heart.
With the rear case removed, you might drape a clean towel over the guts to let it warm up as it would if cased. When you notice the distortion going away, remove the towel and start spraying short bursts at the cylindrical parts, mostly those of 'medium' size ranging from ~ 3/4 to 1 1/2 inches in height and 1/2 to 3/4" in diameter. These are the parts with values most likely to be failing.
If you can identify the power transformer, a largish block, mostly black, check those capacitors first. You will need a mirror to watch the screen for the worsening of the distortion again and be patient; the parts you are cooling have some thermal mass so the effect is not immediate.
If you find one that seems to affect the picture, then, if you have one, direct a hair dryer (blower type) at that area to see if you can recreate the problem several times.
If you can isolate one specific part, note the value of it; it will have several printed items: - Capacitance - this will be such as this: '100 uF' - Voltage - '63V' - Polarity - this will be marked with a '+' and maybe a minus on the other leg. This is important! Any new part must be installed with the correct polarity if any is shown and it will be present on this type of part.
These parts are very inexpensive so if you cannot decide which one is at fault, replace all of them in that area; they cost from 20 cents to a buck. If you have no local electronic parts store (Radio Shack doesn't have much any more) you can order them from Mouser Electronics. Mouser has NO minimum charge and adds only real postage/shipping charges. You'll find them at
If you decide to go this route, you will have to acquire and learn to solder with a soldering iron. Or if you have a friend who is an amateur radio operator, they will probably do this for you.
Removing the board from the bottom of the case is pretty easy, just make sure the monitor has been OFF for a while otherwise removing the thick cable from the CRT will be a really memorable experience!
Looking at the bottom of the board, note the look of the other solder joints there and do your best to duplicate them when installing the new part(s), bad solder joints can make your repair futile.
Or, you can stuff the wole thing in an envelope and send it to me ;-)
If you have been happy with this unit, it is worth the repair, since LCD monitors are often dead soon after the warranty has passed on.
Good luck

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mt, the 6 to 8 lines you were seeing were most likley the prelude to the end of the monitor. If the problem only occurs when the screen saver comes on then I could say the driver maybe being corrupted by a certain screensaver picture or program. When the monitor warms up to a certain temprature the electronics start to fail. You may want to turn off the monitor while your not right in front of it to cool it down and prolong its use.

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