Re: TCL 40S325-CA backlights, sound, no picture
Okay, I jumpered VGH to the side COF and got picture. Unfortunately huge horizontal lines are running across the screen. Spent enough time on this one, so I’ll scrap it for parts and take the rest to the dump!
RIP!
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Last Activity: 07-05-2022, 02:04 PM
Joined: 06-13-2022
Location: Sudbury, ON
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Re: TCL 40S325-CA backlights, sound, no picture
Any YouTube videos, or previous posts that I can use to help educate myself about doing this?...Leave a comment:
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Re: TCL 40S325-CA backlights, sound, no picture
I don't think it will... there's no dedicated TCON board. The signals seem to be passed-through one driver board to the other.
I think the tape cut off method _might_ work if the problem were on the panel driver board that's daisy chained off the main panel driver board (see first set of pics). However, the VGH trace that I severed is on the "main" panel driver board that has the LVDS connector going to it from the mainboard....Leave a comment:
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Re: TCL 40S325-CA backlights, sound, no picture
Attached are some more pictures of the panel driver board that I've been poking at.
Apologies, but the last two pictures seem to have been uploaded and rotated 180!...Leave a comment:
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Re: TCL 40S325-CA backlights, sound, no picture
Okay, I did a bit of troubleshooting. Of the two FPC cables that join the two driver boards, I found where VGH/VGL are and disconnected that ribbon cable.
I turned on the TV but VGH/VGL is still missing, so it's not the secondary (left-side) driver board.
Since this is a trash TV, I had nothing to lose so I found where VGH was going to to the COF flex on right-side driver board and cut the trace. I turned on the TV and got VGH=23V and VGL=-7.98V. A bit of success!
But still no picture....Leave a comment:
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Re: TCL 40S325-CA backlights, sound, no picture
This is very good information. Thank you!...Leave a comment:
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Re: TCL 40S325-CA backlights, sound, no picture
Ugh ok, I'll track down why VGH and VGL are gone.Leave a comment:
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Re: LG 55LB5900 backlight flashing
I've had a number of these LG LB models that flash. Generally I try to replace the LEDs that are open or short or with the highest forward voltage. However, if it's more than four or five LEDs to replace, then I order the strips.
It's also a crap shoot getting the LED diffusers back in the right spot. Most of the time I win, but sometimes I lose!Leave a comment:
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TCL 40S325-CA backlights, sound, no picture
Hello, another TV found on the sidewalk here.
I have a TCL 40S325-CA ROKU LED TV. The backlights turn on, I can hear the typical Roku click sound when pressing the power button (no remote unfortunately) but nothing is displayed on the screen.
Power supply:
Main board goes into standby, so no reason to suspect anything here. Backlights turn on, etc..
Driver boards:
I have 12V going on both sides of the fuse on the panel driver boards.
VGH and VGL are around 1V when powered on.
No shorts to GND on any of the... -
Re: LG 43UM6910PUA backlight on, but no picture
Excellent!!!Leave a comment:
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Re: LG 43UM6910PUA backlight on, but no picture
FYI I taped up about 15 pins and got a semi-stable picture. I reduced the number of taped pins by 1 repeatedly until I got a picture that looked good to me. At the end of the procedure, I had stopped at about 11 pins.
Not quite the fix that I was hoping for, but spending hours beeping out caps and resistors, and measuring resistance, and then comparing to the other driver board led to my wits end when everything matched up.
Good enough for a garage TV!
Thanks for the help everyone!Leave a comment:
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Re: LG 43UM6910PUA backlight on, but no picture
Ahhh, I see -- the third picture in the top is actually a picture of the GOOD driver board. The good board and suspect board are mirror images of each other.Leave a comment:
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Re: LG 43UM6910PUA backlight on, but no picture
Here are two more pictures with the ICs on the LCD PCBs. Please let me know if you need more!...Leave a comment:
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Re: LG 43UM6910PUA backlight on, but no picture
Hmmm. Which blurred area you referring to?
The pictures are of the driver board PCB so it's narrow -- anything blurred is in the background. The blue/cyan is just a towel on my table.
Apologies if I misunderstood!Leave a comment:
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Re: LG 43UM6910PUA backlight on, but no picture
Here are some closer shots of the driver board.
The LVDS cables are coming from the main board as opposed to a separate TCON board -- there's a photo of that set up in my first post.
Thanks everyone for the help so far!...Leave a comment:
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Re: LG 43UM6910PUA backlight on, but no picture
My apologies, I tested the resistance with the ribbon cables attached. With the cables disconnected, I get OL on both good and suspect driver boards with my ground attached to the respective driver board.
With only the GOOD driver board connected these are its voltages when the backlight turns on:
AVDD 17V
VCOM 5.87V
HAVDD 7.85V
VCC 1.83V
For the suspect driver board voltages, they're all 0V when the backlight turns on.
Also, I don't see VGH or VGL test pads... are...Leave a comment:
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Re: LG 43UM6910PUA backlight on, but no picture
Thanks, here are the resistances:
CLK1..6 = 14.7MOhm
VSS = 1kOhm
STV = 17MOhm
EVEN = 14.7MOhm
ODD = 14.7MOhm
The resistances on both boards are the same
Leave a comment:
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Re: LG 43UM6910PUA backlight on, but no picture
Yeah, all of the voltages on the test pads of this suspicious driver board go to 0V after power on.
The other driver board (with the suspicious one disconnected) have voltages present on ODD/EVEN/STV/VSS/CLK1..6.Leave a comment:
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Re: LG 43UM6910PUA backlight on, but no picture
I checked all the capacitors and no shorts. All of the resistors appear fine too.
I checked for shorts at the test points as well and those appeared fine too.Leave a comment:
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LG 43UM6910PUA backlight on, but no picture
Hello,
An LG 43UM6910PUA was donated to me. The backlights turn on and the voltages on the power supply are good. The mainboard appears to leave standby but the LCD stays off.
Disconnecting the right-side LVDS ribbon cable turns one half of the LCD black. Now if I measure voltage at the AVDD test pad on the connected left driver board, I get 17V.
If I re-connect the right LVDS cable, then the AVDD test pad on both of the driver boards goes to 0V. If I only connect the right-side LVDS cable, then the right driver board's AVDD test pad is still 0V....
No activity results to display
Leave a comment: