Hello all,
I recently joined this forum looking for help and expertise in something I really didn't want to deal with -- I was settling in to watch the NBA playoffs when my 50" Samsung LED HDTV's screen went dark. It had been working fine, was purchased in July 2014, and up until now I had no real complaints. My background is EE so here's what I found when I dug into it... Screen was very dark "bluish" color, backlights were lit, sound seemed OK although my cable box is HDMI to a Bose Home Theatre, then that out to TV so I don't know if TV sound was OK or not. "Clicker" sound on TV was fine, and I could tell I was moving within the menu system, so everything seemed OK just no picture.
I read up on things and decided to try a TCON board (off Ebay) -- same problem. I then got a used Main board (also off Ebay) -- same problem.
So I capitulated and started checking voltages -- a real drag without schematics! Everything looked OK except AVDD which was around 1.2V. With the ribbon cables to left and right panel disconnected from TCON, that value read 15V... OK something going on here. Left ribbon cable connected (right side of screen) AVDD = 1.2V, no picture. Left ribbon cable disconnected and right ribbon connected, AVDD = 15V and left side of screen works OK. So something is going on with the right side of screen. There looks like a few MLCC parts along the lower PCB "strip" connecting the right side of panel that are between AVDD and GND. A few diodes, other MLCC parts, resistors, etc. Nothing is shorted though, I read about 20K from a DMM with the panel disconnected between AVDD and GND on the strip itself. Also OPEN in one direction and DIODE in the other with DMM set to 2K/DIODE position (as far as I can tell both left and right panels read the same here). The tabs look OK too, at least as far as I could tell. The TCON board has an LED marked VREF which lights and stays lit when only the working side panel is connected (with OK video on that side). When reversed and the "bad" panel is connected, the LED lights momentarily then goes out. The picture also comes on briefly on the "bad" side then fades to dark as AVDD goes down -- which takes about 2 or 3 seconds from power on.
So whatever is going on is not a dead short, but something that happens as time goes by, maybe a voltage breakdown or beginning of some kind of runaway which causes TCON to current limit. Of course it would be great if it was an MLCC or an SOT-23 "something" I saw on that PCB strip that has pin 3 tied to AVDD, but since I don't have much experience with panels can someone say this is a typical panel failure symptom? MLCC's usually short and this isn't, but maybe breaking down? Not sure what the SOT-23 is tied to AVDD but I could look at that too. I could also drive this section's AVDD externally through a diode and try and bring it up slowly and see what "lets go" or gets hot first! lol. With the finger test I could not tell anything on the PCB strip was getting warm. I'd love to save this TV if possible, so looking for a little advice and wisdom from anyone that might have "been there done that" before! I do have the capability of removing the 0402/0603/SOT-23 SMT parts along that "strip" PCB too just to get them out of the picture. I could also take a current probe and actually see the overload or scope anything else that anyone thinks would be worthwhile. This TV has an "AH01" revision after the main part number. I think that refers to the panel's manufacturer but I'm not 100% on that. Thanks in advance for any help, and if I left anything out or can provide more information please let me know. This was my first post so please bear with me! A picture of my TCON board is attached if that helps.
I recently joined this forum looking for help and expertise in something I really didn't want to deal with -- I was settling in to watch the NBA playoffs when my 50" Samsung LED HDTV's screen went dark. It had been working fine, was purchased in July 2014, and up until now I had no real complaints. My background is EE so here's what I found when I dug into it... Screen was very dark "bluish" color, backlights were lit, sound seemed OK although my cable box is HDMI to a Bose Home Theatre, then that out to TV so I don't know if TV sound was OK or not. "Clicker" sound on TV was fine, and I could tell I was moving within the menu system, so everything seemed OK just no picture.
I read up on things and decided to try a TCON board (off Ebay) -- same problem. I then got a used Main board (also off Ebay) -- same problem.
So I capitulated and started checking voltages -- a real drag without schematics! Everything looked OK except AVDD which was around 1.2V. With the ribbon cables to left and right panel disconnected from TCON, that value read 15V... OK something going on here. Left ribbon cable connected (right side of screen) AVDD = 1.2V, no picture. Left ribbon cable disconnected and right ribbon connected, AVDD = 15V and left side of screen works OK. So something is going on with the right side of screen. There looks like a few MLCC parts along the lower PCB "strip" connecting the right side of panel that are between AVDD and GND. A few diodes, other MLCC parts, resistors, etc. Nothing is shorted though, I read about 20K from a DMM with the panel disconnected between AVDD and GND on the strip itself. Also OPEN in one direction and DIODE in the other with DMM set to 2K/DIODE position (as far as I can tell both left and right panels read the same here). The tabs look OK too, at least as far as I could tell. The TCON board has an LED marked VREF which lights and stays lit when only the working side panel is connected (with OK video on that side). When reversed and the "bad" panel is connected, the LED lights momentarily then goes out. The picture also comes on briefly on the "bad" side then fades to dark as AVDD goes down -- which takes about 2 or 3 seconds from power on.
So whatever is going on is not a dead short, but something that happens as time goes by, maybe a voltage breakdown or beginning of some kind of runaway which causes TCON to current limit. Of course it would be great if it was an MLCC or an SOT-23 "something" I saw on that PCB strip that has pin 3 tied to AVDD, but since I don't have much experience with panels can someone say this is a typical panel failure symptom? MLCC's usually short and this isn't, but maybe breaking down? Not sure what the SOT-23 is tied to AVDD but I could look at that too. I could also drive this section's AVDD externally through a diode and try and bring it up slowly and see what "lets go" or gets hot first! lol. With the finger test I could not tell anything on the PCB strip was getting warm. I'd love to save this TV if possible, so looking for a little advice and wisdom from anyone that might have "been there done that" before! I do have the capability of removing the 0402/0603/SOT-23 SMT parts along that "strip" PCB too just to get them out of the picture. I could also take a current probe and actually see the overload or scope anything else that anyone thinks would be worthwhile. This TV has an "AH01" revision after the main part number. I think that refers to the panel's manufacturer but I'm not 100% on that. Thanks in advance for any help, and if I left anything out or can provide more information please let me know. This was my first post so please bear with me! A picture of my TCON board is attached if that helps.
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