Samsung LCD repair questions

[seahunt]

I'm hoping someone could help me out with this:

I have a Samsung LNT4065FX tv. It is about 7 yrs old.



I am trying to troubleshoot and narrow the problem down. The caps were replaced about two yrs ago through Samsung . The tv worked fine after the caps were done. Recently the screen started flashing (strobes) on/off. Not power cycling or anything but just flashing. It has audio and video but the screen flashes/strobes when input is through one of the HDMI ports. When I changed to the second HDMI port it continued to flash but there was no audio or video. It flashes check signal input.



I changed the source (play station 3) through HDMI and got the same results.



I changed the source and plugged the cable directly into the TV and it worked fine.



The capacitors visually look ok so I don't think it is that.



I've tried different HDMI cables so negative on the cables.



The firmware seems to be up to date on the TV.



I should mention that this all started when the TV lost video but had sound. I took it to a repair tech to get it checked out. He could not find anything wrong with the TV. He never opened it up or did anything to the TV other than hook a blue ray player up. This after the TV sat unplugged for several weeks. I brought the TV home and it continued to work fine. After a period of time it started the screen flash/strobe. I was thinking it may be a heat problem and whatever it was causing it was cooling down enough to get it going again. I left the TV alone for a few weeks and then fired it up again. The flashing is happening with the TV cold.



So, I'm thinking it is the main board is the culprit. I am probably going to replace (if I can find a board) but before I did I wanted to get some other opinions on the problem.



Thanks for any input. Clint

[johnboy1313]

Re: Samsung LCD repair questions

Take the back off and post clear pictures of the boards inside the TV.

[Maxstang]

Re: Samsung LCD repair questions

This sounds like cold solder joints on the CFL transformers. Given the age of the tv, it makes sense. I'm not familiar with this model, but they are probably on the power board.

[snipersquad100]

Re: Samsung LCD repair questions

I had a the same problem with a bush tv not so long back. Every souse would work except the hdmi. I had to change the main board to fix it.

[seahunt]

Re: Samsung LCD repair questions

Guys, I had to go to work. I appreciate the replies. I will upload the pics later today. The thing with the CFLs is the TV works fine with cable straight into the TV. The problem arrises when I go to the HDMI input. Again, I'm thinking Main or TCON board. Sniper I hope it is the main board like the problem you had.

[Ltank]

Re: Samsung LCD repair questions

Are the cables making a good solid connection? Check the DCV from the PS to the inverter that it is what is labeled and steady, usually 24vdc. If there is a backlight on comand from the main board check that too that it is constant and not strobing. get a picture of the inverter boards with the shielding removed so we can see. look at the big capacitors on the inverter boards that they are not leaking or bulging. if all the above looks good try replacing the the capacitors with good low ESR caps.

[budm]

Re: Samsung LCD repair questions

"I changed the source and plugged the cable directly into the TV and it worked fine." So it does flash when using cable, or composite video, or RGB video? But HDMI, it will flash?

[seahunt]

Re: Samsung LCD repair questions

budm, I haven't tried composite or RGB as of yet. I don't have those available right now. It does not flash when the cable is plugged in to the set. Only when HDMI is used. I should have been clearer. I found some info about screen flicker and possible causes. Thats not it at all. It is more like a stobe effect where the whole screen goes in and out.

Tank, the HDMI is making a solid connection.
HDMI port 1: I get audio and video with the stobe
HDMI port 2: I get no audio or video. No signal input messagae and the stobe.

[xredhawk]

Re: Samsung LCD repair questions

turn down the backlight in settings see if it still strobes

[splitcrete]

Re: Samsung LCD repair questions

Check your solder joints. I had the same problem, and everything was ok when the set warmed up.I Reworked the joints ,and it has been working ever sense.