LCD TV repair - Page 1
Forum section: electronics / repair

author: HinesNetwork
author_rank: Contributor
timestamp: January 14, 2013, 02:53:18 am
content: I'm hoping someone can point me in the right direction for repairing my Sony LCD TV. The TV has horizontal lines on it for all of the inputs, however if the coax (antenna) input is using the over the air inputs it doesn't have the lines. If for example I hook up a direct tv box using coax to the input I get the lines again. But, if I connect the direct tv box to the TV by just connecting the center pin of the coax (although the image isn't complete) the lines on the LCD go away. This leads me to believe the issues has something to do with the external components being coupled to ground. Does anyone have any ideas what I might check on the tv to figure out why this is happening?Side note: I just got my digital oscilloscope and can test things, I'm just not sure where to start.Thanks for an help you can give.Jason

author: Psi
author_rank: Super Contributor
timestamp: January 14, 2013, 03:03:46 am
content: Yeah, it does sound like a grounding issue is involved.If it was me, the first thing i'd do is try a coax TV signal isolator and see if it fixes the problem. If it does i'd probably just leave it on and forget about the problem.But if you want to fix it then i'd probably look at the components around the RF input section. It's possible that a capacitor in there has become shorted and something is getting earthed that shouldnt be.(Side thought. I have seen lines on a TV when someone had a powerful RF distribution amps feeding their TV directly and the signal was way to powerful for the TV to handle.)

author: zaoka
author_rank: Frequent Contributor
timestamp: January 14, 2013, 03:14:57 am
content: Can you post a picture?

author: HinesNetwork
author_rank: Contributor
timestamp: January 14, 2013, 04:28:21 pm
content: I guess I should have said this in my first post, oops, but the issue is really that I'm getting lines on all the inputs (HDMI, AV, etc.). I don't usually use the coax input, I just found while troubleshooting that the coax input doesn't have the problem if it has an antenna or nothing hooked up to it. But as soon as I hookup my direct tv box via the coax the lines show up. My goal is really to repair it so the lines don't show up on the HDMI inputs.Here's an image of the coax input, without anything connected, with a menu up:http://note.io/13uVj25This is an image of the HDMI input:http://note.io/SytftmThanks,Jason

author: tom66
author_rank: Super Contributor
timestamp: January 14, 2013, 04:41:07 pm
content: I would advise re-seating the LVDS cable. This is the cable which runs from the main board (AV inputs) to the T-con board (usually under a shield, connects to the LCD panel.)

author: HinesNetwork
author_rank: Contributor
timestamp: January 14, 2013, 04:50:19 pm
content: Quote from: tom66 on January 14, 2013, 04:41:07 pmI have tried re-seating the cable, no luck. I've also tested the voltages going to those boards and they max at 12.2 V and min at 11.7 V

author: tom66
author_rank: Super Contributor
timestamp: January 14, 2013, 04:58:09 pm
content: Seems a little unstable.Is this definitely made by Sony? (Not an OEM rebadge like they've started doing.)

author: HinesNetwork
author_rank: Contributor
timestamp: January 14, 2013, 04:59:40 pm
content: Quote from: tom66 on January 14, 2013, 04:58:09 pmYes it's a genuine Sony.

author: HinesNetwork
author_rank: Contributor
timestamp: January 14, 2013, 05:26:12 pm
content: Quote from: tom66 on January 14, 2013, 04:58:09 pmWhen you say unstable are talking about the voltages?

author: sherlock
author_rank: Contributor
timestamp: January 15, 2013, 03:38:08 pm
content: I'm a bit conused... Do younormallyhave the tv box hooked to the coax input of the tv? I have a Sony (no problems yet) and the cable box, DVD, and Media player are all connected although you obviously only use one at a time. It sounds like you only have stuff like a DVD player, etc. hooked up and NOT the tv (cable?) box. If the problem goes away if you disconnect the tv box and any other media is fine, then I'd suspect the tv box and not necessarily the tv. Any way you can try another tv box and see if the problem remains? If it really is the tv, I'd look at the power supply first. I remember that Samsung had a capacitor problem a year or two back with some of their tvs. I think it was sound related though. Good luck with it.sherlock

author: HinesNetwork
author_rank: Contributor
timestamp: January 15, 2013, 03:56:54 pm
content: Quote from: sherlock on January 15, 2013, 03:38:08 pmI don't usually use the coax, I just found it strange that the problem goes away, only when using an antenna (or nothing) on the coax. I have a blu-ray, Apple TV, and direct tv hd box that all use the HDMI inputs.The out put of the power supply seems okay to me, it varies in voltage a little but it didn't seem that bad to me, if I'm wrong about that please correct me.

author: tom66
author_rank: Super Contributor
timestamp: January 15, 2013, 10:02:22 pm
content: How about some pictures of the chassis. I do not know if this uses 24V inverter or high voltage backlight driver on the PSU directly.

author: HinesNetwork
author_rank: Contributor
timestamp: January 17, 2013, 01:51:23 am
content: Quote from: tom66 on January 15, 2013, 10:02:22 pmThis is the input board:http://note.io/VnUftZThis appears to be the backlight power supply:http://note.io/V6gx2hThis is the main power supply:http://note.io/VnUC7ILet me know if these images aren't good enough, I took them at night so it was hard to get the light right.Thanks,Jason