Having problems with your LG Flatron F700B 17" CRT Monitor ?

LG f700b raster problem

\015 Hellomy monitor is LG f700b.when i turn it on there are some raster lines at the top of screen that reversed to down (about 2 cm) .top of screen is blank because that lines are my monitor top screen.about 2 hour after turning monitor on this problem decreases. thanks for every one help\015

Answers :

If the lines are slanted, you are seeing 'retrace' of the horizontal sweep.\015\012The 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.\015\012
\015\012If 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.\015\012
\015\012Go to any electronics parts source and buy two cans of 'freeze spray.' \015\012Expect to pay $4-5 dollars each for them.\015\012Using 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.\015\012
\015\012With the rear case removed, you might drape a clean towel over the guts to let it warm up as it would if cased.\015\012When 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.\015\012These are the parts with values most likely to be failing. \015\012
\015\012If you can identify the power transformer, a largish block, mostly black, check those capacitors first.\015\012You 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.\015\012
\015\012If 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.\015\012
\015\012If you can isolate one specific part, note the value of it; it will have several printed items:\015\012- Capacitance - this will be such as this: '100 uF' \015\012- Voltage - '63V' \015\012- 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.\015\012
\015\012These 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.\015\012If you have no local electronic parts store (Radio Shack doesn't have much any more) you can order them from Mouser Electronics.\015\012Mouser has NO minimum charge and adds only real postage/shipping charges.\015\012You'll find them at mouser.com \015\012
\015\012If you decide to go this route, you will have to acquire and learn to solder with a soldering iron.\015\012Or if you have a friend who is an amateur radio operator, they will probably do this for you.\015\012
\015\012Removing 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!\015\012
\015\012Looking 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. \015\012
\015\012Or, you can stuff the wole thing in an envelope and send it to me ;-)\015\012
\015\012If 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. \015\012
\015\012Good luck
Repair Help & Product Troubleshooting for LG Flatron F700B 17" CRT Monitor

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