Thank you in advance for reading if you have the time!Ok, full disclosure: this is another Goodwill find, so any repair short of buying a new, equivalent monitor is a win.
(Looks like equiv units go for about $200-250 new.)
First, see video of failure mode, as it is worth 10,000 words (sorry for the quality, not the best):
https://youtu.be/ztuk_H6ZwrY(Display mode is "duplicate" in Windows, happened before and after OS upgrade. Picture is being sent over HDMI at native display settings for the Samsung (1080p, 60-ish hz. Failure is independent of what input is selected (monitor has 1 HDMI and 1 VGA). OSD menu and overlay are also affected.)
Monitor worked flawlessly for about 6 months in my house. Then the issue in the video and pictures attached started happening (probably why it went to Goodwill). Happens at power-up for 30-60 seconds, then snaps to a good image. At first, it only happened occasionally, maybe 1 in 10 power-ons, then became for frequent over a few months. Now it happens every 99 in 100 power-ons, and can last for up to 15 minutes before snapping to a good image. (By "snapping", I mean that there is no transition from failure to a good image, it corrects itself instantly, albeit at a random time.) The monitor displays the top-left 1/4 of the input, stretched across the whole LCD. It is green-tinted and each row of pixels wavers back-and-forth quickly. Framerate seems to be normal.
Topology of monitor:
- External power brick, inputs 14V, rated at 4A. Voltage under load is within .2V and stable.
- Monitor has a main logic board with inputs and DC jack. Capacitive front bezel controls and LED backlight run off this board.
- Ribbon cable from main logic board goes up to LVDS board (correct term?) which is hot-barred to the LCD flat-flex.
Things I have tried so far:
- Caps are good brand, well-rated. Can't see any obvious failures there. Looked under magnification for solder issues.
- Thermals. The two chips on the main logic board get pretty warm (~75°C). Freezer spray had no effect on any part of the power/logic board, cables, or LVDS board/flex.
- Early troubleshooting seemed to point to the LVDS ribbon cable, as it was starting to delaminate where it is folded over. I replaced it with an official Samsung part from samsungparts.com. Issue remains. Oh well, only $13.
- Again, to reiterate, other input sources do not fix the problem. LCD menu is affected.
- Reset display settings on the monitor, made sure refresh rates, etc were being detected correctly.
- Several in-depth searches turned up no similar issues reported on other corners of the internet.
- Putting pressure on or flexing the LCD flat flex where the chip-on-flex drivers are doesn't seem to have an effect. Neither does messing with the hotbar areas or other connectors/caps/components.
- UPDATE: Tried powering the montior from a universal DC supply set at 14V, got the same issues.
Official service manual attached, not very thorough, I'm afraid...
Can anyone who has a better understanding of LCDs hypothesize here?
More pics:
Dropbox link for the service manual!Sorry for the long post.
TLDR is totally understandable.