LCD TV with extreme ghosting - Page 1
Forum section: electronics / repair

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 10, 2014, 06:42:15 pm
content: I have here a Philips 37PFL5603D/10 from my daughter that keeps me puzzled.At her house the picture went very dark after 10 minutes from switching it on, so I took it home to check the backlights and the inverter. Of course at my house it did not turn dark, even after a few hours, not even when I put the back on it again, thought it might be heat related, but no. What I did notice is that the overall brightness was a bit low, so it could be time to replace the backlights. Reading on the 'net made me think that it could have something to do with the firmware, several people mentioned that they had brightness variations that went away after updating. Ok, not really what I had seen but it couldn't hurt could it?Allright, after updating the brightness is much better and the picture looks very nice. But... It has some weird kind of ghosting. For instance, when I turn on the menu, leave it on screen for 10 seconds and then turn it off, I can still see it in the normal picture,even when I cut the power for 15 seconds and then turn it back on. It's almost like the LCD has a memory of it's own, I have no other explanation for it. And I don't mean standby mode, I really pull the plug from the mains.I can't remember seeing this before I updated the formware, but really... what's going on?Any ideas welcome!

author: romantronixlab
author_rank: Regular Contributor
timestamp: August 10, 2014, 07:20:49 pm
content: When the cover was off, did you check condition of components, mainly the capacitors? I had one Vizio TV acting once because of out of specs capacitors.

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 10, 2014, 07:57:42 pm
content: Quote from: romantronixlab on August 10, 2014, 07:20:49 pmCapacitors all looked fine, one thing I noticed is that the capacitors at the backlight connection (22p, 6Kv) heated up to 100C, not sure if that is normal...

author: FrankenPC
author_rank: Unknown
timestamp: August 10, 2014, 08:40:07 pm
content: Do LCD's have a internal processor using a frame buffer? Sounds like the frame buffer mechanism is damaged somehow.

author: Rasz
author_rank: Super Contributor
timestamp: August 11, 2014, 12:51:03 am
content: firmware upgrade fixing backlight brightness is weird enough, sounds like tv goes into some kind of power saving mode? unless it wasnt backlight, but tcon problemghosting is tcon related, panel might be overdriven leaving semi permanent post imagesfirmware upgrade never touches tcon, so I fail to see how upgrading firmware could result in this bug

author: simplifyiyuk
author_rank: Contributor
timestamp: August 11, 2014, 06:22:13 am
content: Did have this issue with a few 26" LCD TVs the picture would be dark and ghosting can confirm that T-Con was the issue in that case. Never got as far as component specific troubleshooting but my guess would have been the panel drive voltage. this is usually from a DC-DC converter on the T-con board. its model specific but I'd be expecting 17-18v yours is probably lower than it should be.so in summary:Either the feed voltage coming up the LVDS is low (unlikely as your picture is showing)orThe panel drive voltage is low/fluctuating/wrong.(my bet)

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 11, 2014, 09:11:38 am
content: QuoteWell, anything that is buffering something should be empty after removing the supply power for 15 seconds.QuoteI upgraded the firmware because there was talk about unstable brightness that would be fixed, not exactly what I noticed but still.I think it wasn't a power saving mode, you'd expect the display to go blank but it just lost 50-80% of the brightness, leaving a dark, overcolored picture.QuoteI'm not saying that it was introduced by the update, it's just that I didn't notice it before that. Having said that, it is so strong that I really think I could not have missed it if it was there before the update. If I switch channels the logo from the previous channel stays on screen for minutes, even after power cycling.QuoteYes, I guess I should start measuring some voltages, exactly what I always tell others...I have the service manual for the chassis used so that will help.

author: Rasz
author_rank: Super Contributor
timestamp: August 11, 2014, 10:22:18 am
content: Quote from: Rasz on August 11, 2014, 12:51:03 amor under driving = too weak to change from the previous crystal positions = ghostingwould also explain weird dark images with oversaturated colorsusually some caps go bad on tcon board

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 26, 2014, 07:32:26 pm
content: Replaced the AS15-F on the T-CON board: Problem solved!