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LG 21FU3RLM 21" CRT TV Issues    
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atesfaye



Joined: 01 May 2014
Posts: 6

PostPosted: Thu May 01, 2014 11:05 am    Post subject: LG 21FU3RLM 21" CRT TV Issues Reply with quote

Hey guys, I have had an LG 21FU3RLM tv for about 4 years, bought new. The problems began about 3 years ago when a lightning strike occurred nearby the house and resulted in it not degaussing correctly. This was eventually fixed by using a degaussing coil.

About a year ago the TV began to show slightly inclined red horizontal lines and the background became reddish and picture would be overshadowed by this reddish background and horizontal lines. When I switch it off it seems like there is a horn like looking symbol at the center for a split second before screen goes dark. I took it to a repair shop and he diagnosed it as the screen going bad and the board being ok, degaussed it and returned it to me. I believe he at first thought that the fly-back was going bad and had played around by adjusting it and realized it was ok, when he tried my board on another similar LG tv.

By adjusting the screws on the the back of the fly-back I was able to remove the red shadows and lighten the picture. The screen had noticeably become darker though, for example I had to manually create my own "user" setting for brightness contrast etc, as the factory presets such as "game, mild, etc." had become too dark. The This worked for a few months.

Now a few weeks ago the tv was on standby all night and when I woke and turned it on the colors were all messed up again (needs to be degaussed again). I use a FTA satellite receiver and couldn't find the remote as the FTA receiver is next to the tv, I began to change the channels manually on the front of the box of the FTA. What happened next is shocking as I heard a buzzing noise and saw the images on the screen change shape as if a magnet had been moved a cross the screen. I immediately heard a zap sound and smelled smoke. Being a computer technician I figured a fuse was probably blown and opened up the tv to confirm my suspicion. I bought several fuses in case and replaced it and it immediately blew the fuse, so I knew something else was damaged. I looked at the board with interest and found the the posistor was toasted literally, and had melted.


Today I replaced the posistor and got no picture, so I adjusted the settings on the fly back and I had picture and sound but it was blurry. I fine tuned some more and had got it to a decent setting, assumed all was good and put it back together.

The problem is now when I change channel on the satellite the picture immediately becomes blurry
When I turn off and restart sometimes I get no picture, don't get it right away or it is blurry
Audio always works
It is no longer blowing fuses, the remote works
When I put it in normal antenna mode with no antenna connected it is supposed to be snowy but it is blizzardly as if the refresh rate is too high or something.

Is it possible this is due to a bad posistor or bad soldering of the posistor, as I do believe I am not the best solderer in the world, or other damage?

Attached are some pics, sorry they are poor quality, 2 show CNN as blurry, 1 shows the snow and one shows what is supposed to be the Green AV1 sign that is supposed to show on a black background as blurry.


Thanks for your help.
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atesfaye



Joined: 01 May 2014
Posts: 6

PostPosted: Thu May 01, 2014 11:35 am    Post subject: Reply with quote

Below are the images.








kuhurdler



Joined: 28 Dec 2006
Posts: 2852
Location: Overland Park, KS

PostPosted: Mon May 05, 2014 10:07 am    Post subject: Reply with quote

Turn up the screen voltage to where it shows retrace lines, then back it down until they disappear.
Then adjust the focus knob back and forth, back and forth until you can find the sweet spot just in the middle.

I'd also check your B+ voltage. I have no idea what it is supposed to be for this model though. It does sound like you have power supply issues.
atesfaye



Joined: 01 May 2014
Posts: 6

PostPosted: Wed May 07, 2014 6:00 am    Post subject: Reply with quote

kuhurdler wrote:
Turn up the screen voltage to where it shows retrace lines, then back it down until they disappear.
Then adjust the focus knob back and forth, back and forth until you can find the sweet spot just in the middle.

I'd also check your B+ voltage. I have no idea what it is supposed to be for this model though. It does sound like you have power supply issues.


Do you mean the adjustments on the back of the flyback? Cause they don't seem to make much of a difference, before I could fine tune them so texts, ie., stock / news tickers, were sharp but now it doesn't make much of a difference, especially the focus knob, it doesn't seem to have the same effect as before. I think the screen voltage is the one where it controls how dark or light it is, on the back of flyback right? That one does make a noticeable change if I turn it clockwise or counterclockwise controls how light or dark the picture is.

Not sure what B+ voltage is.

Obviously the posistor is soldered on, since it seems to work. Before the posistor melted the screen needed to be degaussed, after I replaced the posistor the degauss problem also left on its own.

My problem now is:

If I turn on the TV and I get no Video, I have to turn it off from the power switch and wait like a couple of hours for it to show video again. If it is on standby and I turn it on it won't display video.

If I switch it off or put it in standby and power it on right away, I get no video.

If it does show video, it fluctuates from being blurry to clear to blurry intermittently, I mean constantly.
When I change channels it becomes blurry right away and clears up in like 30 seconds, and becomes blurry within a few seconds, different degrees of it. It's like it is squinting all the time.

Could this be due to a poor quality posistor or damage sustained when the original posistor melted and fuse blew?

I have a schematic of the board, a service manual I can upload.

Thanks.
atesfaye



Joined: 01 May 2014
Posts: 6

PostPosted: Tue May 13, 2014 1:32 pm    Post subject: Reply with quote

Solved guys; It was as simple as the red cable from the back of they flyback being disconnected. I assume this happened when I flipped the board over to solder the new posistor.

Interesting note, the black cable from the flyback to crt neck has a clip on it to keep it in place while the red one doesn't and just slides in.

It's almost as good as new. Now I can watch the world cup, yay!!!!
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kuhurdler



Joined: 28 Dec 2006
Posts: 2852
Location: Overland Park, KS

PostPosted: Wed May 14, 2014 7:06 am    Post subject: Reply with quote

Thanks for posting back.

Now I'm very curious. You're saying those pictures were taken with the largest red anode cable completely disconnected? (That doesn't seem possible to me)

Or is there a smaller red cable going from the focus adjustment?
atesfaye



Joined: 01 May 2014
Posts: 6

PostPosted: Wed May 14, 2014 3:10 pm    Post subject: Reply with quote

Yes, there are only two cables going from the flyback to the crt neck or even the crt, all other wires connect directly to the board or behind the crt yoke. In my case it was the red one and not the black one that had come disconnected. Wish had taken a pic before putting it back together.

I guess the red wire wasn't supplying constant and consistent voltage to the flyback and crt since it was disconnected. Interestingly the position and locatiion of the wire caused me to not notice anything unusual, especially since after I replaced the posistor I got audio and video. I figured some damage had occured. Had I had no power or audio, I would've checked all the wires for loose connections etc.
JTS1957



Joined: 21 Jan 2009
Posts: 2286
Location: Far, Far Away

PostPosted: Wed May 14, 2014 3:36 pm    Post subject: Reply with quote

The Focus lead usually connects to the CRT molded plastic socket, some have a clip or latch that 'locks' it into socket, then the socket pins are connected to the printed circuit board and the other lead (G2/Screen) connects to the printed circuit board.
atesfaye



Joined: 01 May 2014
Posts: 6

PostPosted: Thu May 15, 2014 2:24 am    Post subject: Reply with quote

Ok cool, thanks for the info! I have a question that may be related. There seems to be a red horizontal band or line that shows on the center of the screen from end to end as soon as it is turned on. This happens usually after a cold start (meaning turning on manually from the power switch). The red line is about 2-3 mm wide, what can this be?

Before the fried posistor the tv used to ghost red shadows around people and objects and this was somehow limited by adjusting the setting on the flyback. This made the screen dark, that's how the technician returned it to me.

The TV is almost as good as the day I bought it now. No more degauss issues, no red ghostiing. The picture is crystal clear and amazingly the adj. on the back of the flyback are more precise. I can now see the on screen text like the menus, ch #, vol +- # and settings which I couldn't before.

Also here in my country we have routine power outages. If the tv is left on standby and there is an outtage, when power returns there seems to be a thumping noise(like a heart beat) that comes from it until I turn it on again. Any ideas? I'll try to post the pic of the red line, but it happens so fast, maybe I can upload the thumping noise as well.

Thanks guys!
JTS1957



Joined: 21 Jan 2009
Posts: 2286
Location: Far, Far Away

PostPosted: Thu May 15, 2014 7:48 am    Post subject: Reply with quote

Surges/spikes are not electronic items friends. Better to disconnect from mains if outages are routine (predictable?). Of course that will defeat the 'being turned on/off with remote' and may have to reset certain things, like the clock, for example.

Focus: I adjust for sharpest scanning lines;
G2/Screen: turn up slowly until you see thin, diagonal (retrace) lines, and then down until these disappear, then just a tad further.

I suspect that 'line' may be normal - IF - it is only present at turn on and is NOT affected by tapping on (or flexing) PC board(s). When you post pix/video we might change our mind.
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