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820-3115 No backlight - missing LCD_BKLT_EN
- Thread starter ytesfay80
- Start date
ytesfay80
Member
Ok. So before checking for continuity I decided to flip the cable connecting to the lcd upside down and now I am getting 3.31v on Pins 2 & 3 and the lcd is working but there is no backlight(saw questionmark folder with flashlight) so I will troubleshoot this issue. Thanks for the help if I need anymore I'll reply on this thread.
ytesfay80
Member
I am getting 12.5v on L9701 as well as D9701 and the output of C9799 is a constant 12.5v and in diode mode C9799 measures 0.579 on output. I replaced C9797/C9799 weeks ago as they had some corrosion so I don't think that could be the issue.
BKLT_PLT_RST_L and LCD_BKLT_EN both show 3.3v.
I checked the feedback line of the U9701 LED Driver and it doesn't look burned but I do have a several LP8550's that I can replace it with.
Is this likely a LED Driver issue?
BKLT_PLT_RST_L and LCD_BKLT_EN both show 3.3v.
I checked the feedback line of the U9701 LED Driver and it doesn't look burned but I do have a several LP8550's that I can replace it with.
Is this likely a LED Driver issue?
Last edited:
ytesfay80
Member
dukefawks larossmann Ok so a bunch of confusing stuff has happened since I reflowed the LED Driver. I reflowed it to see if it would work before having to replace it and after reflowing I was getting 12v on pin 3 of Q9706 and Q9707 which is too high and no voltage on the output pins of Q9706.
I replaced Q9707 but that made no difference.
I replaced R9788 and R9789 even though they measured correct resistance because I thought that was causing pin 3 of Q9707 to be so high. I didnt have a donor board for this model so I took the resistors from a 820-3209 that had the same resistance but 1/20w instead of 1/16w(don't know if that is a big issue.)
Now after replacing those resistors I no longer have LCD_BKLT_EN and once again the board isn't seeing the lcd as there is no voltage on Pins 2/3 of the lcd connector and Pin 1(LCD_IG_PWR_EN) of U9000.
The lcd cable and connector look fine so I don't know what could have happened.
I replaced Q9707 but that made no difference.
I replaced R9788 and R9789 even though they measured correct resistance because I thought that was causing pin 3 of Q9707 to be so high. I didnt have a donor board for this model so I took the resistors from a 820-3209 that had the same resistance but 1/20w instead of 1/16w(don't know if that is a big issue.)
Now after replacing those resistors I no longer have LCD_BKLT_EN and once again the board isn't seeing the lcd as there is no voltage on Pins 2/3 of the lcd connector and Pin 1(LCD_IG_PWR_EN) of U9000.
The lcd cable and connector look fine so I don't know what could have happened.
ytesfay80
Member
dukefawks larossmann
Its been a few weeks now and I have tested this board with 2 screens (one used and one new AU Optronics B133EW07) and 2 different lcd cables.
I also replaced the lcd connector and I gave this board an ultrasonic cleaning.
Is there anything else I can check for? [h=1][/h]
Its been a few weeks now and I have tested this board with 2 screens (one used and one new AU Optronics B133EW07) and 2 different lcd cables.
I also replaced the lcd connector and I gave this board an ultrasonic cleaning.
Is there anything else I can check for? [h=1][/h]
JorgePayar
Member
did you replace lp8550?
ytesfay80
Member
No. Louis said earlier in this thread that I shouldn't be worried about backlight if the screen is not even being recognized since I get 0v on Pin 1 of U9000.
this honestly sounds like a clunker at this point. either bad PCH or some broken via inside the board. if you want to torture yourself, this is the board to do it on.