I want to ask what are the components need to be checked and the voltage I should get to have the backlight on. Customer said some water spilled on it but I dont see any corosion which makes a lot difficult for me to find the fault. Thanks
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Last edited by abudo; 02-03-2020, 12:51 AM. -
Re: Need help 820-00840-A no backlight Newbie here
Tried PRAM reset? Image is ok? Check for damage inside LCD connector.
There are a lot of Louis Rossmann videos on no backlight issue (maybe on A1708 as well), I'd recommend to watch them.
Also could be affected by flexgate, but if it happened right after liquid damage that should not be the cause.OpenBoardView — https://github.com/OpenBoardView/OpenBoardView -
Re: Need help 820-00840-A no backlight Newbie here
I have not tried PRAM reset. CapsLock is turning on (not brain dead) and yes I see image. The video from Louis with A1708 was problem with the resistance on gate and source(Q8400) was so low which is caused by capacitor (C8400). Now on my case is that mine is ok with those parts and I dont know whats next to test hehehe sorry for bothering you guys
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Re: Need help 820-00840-A no backlight Newbie here
The troubleshooting process for no backlight is always the same. Measure voltage on backlight output, if it's very low measure resistance to ground as well. Also since this is liquid damaged you'll have hints on the board.OpenBoardView — https://github.com/OpenBoardView/OpenBoardViewComment
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Re: Need help 820-00840-A no backlight Newbie here
yes customer said some water spilled on it, but i dont see any corrosion or any water marks when I checked it. Tomorrow I will be checking it again since it was dayoff yesterday and today. thanks for your response guys it makes and keeps me going. Iam very much open on your suggestions. I will keep you posted and I hope we can get good results. thank you very much.
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Re: Need help 820-00840-A no backlight Newbie here
I already have here an MacBook with serious issues of liquid damage...
I clean well the board and everything goes fine... But system gets stuck and slow sometimes with fan spin very high...
I check well again and it was a little cable with a little corrosion that passed away by my eyes... Try to check if any part have any liquid residue or corrosion clean well all connectors as well and flat cables.
Look for decolored, corrode points at board.
Hope this simple info could help you to figure out anything.
CheersComment
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Re: Need help 820-00840-A no backlight Newbie here
the shop was busy in the past days and i almost forgot about this macbook so heres the number when i check with a connected screen, charger plugged in and detached battery
PP5V_S0_BKLT_A (R8445) is 4.9V
PP5V_S0_BKLT_D (R8444) is 4.9V
LCDBKLT_FET_DRV_R (R8410) is 0.0V
PP5V_S0SW_LCD is 4.9
does this mean that the U8400 is damaged?Last edited by abudo; 02-11-2020, 08:18 PM.Comment
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Re: Need help 820-00840-A no backlight Newbie here
please help. im just a newbie Im suspecting the U8400 IC but i need more opinion from you guysComment
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Re: Need help 820-00840-A no backlight Newbie here
Just check for output. I didn't have this boards yet. But it is always the same. Check output from u8400 , check resistance, if output is present at u8400 -> check the path to the screen. (If u8400 is the bolt boost cuircuit)
Maybe R8410 is broken? Check for power on both sides! Don't rush, take your time.
I don't have the boardview or schematic so I assume all your voltages what you posted are for the screen sense.
Also I remember one case where at screen sense L**** was giving on one side the proper 5v but on the other side only 3V
Plz double check everything. Measure on bklt output at lvds with screen and without!Comment
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this tv is throwing me for a loop. do samsung tvs no longer have the backlight self test feature built into the power supply?
i tested the backlight with my LED tester and it lights up both strips. one of them reads 100v and the other reads 63.7v.
unplugged mainboard from power supply but left backlight plugged in, and then plugged psu wall power in. expected to see backlights light up but see nothing.
according to how ive diagnosed in the past, this would almost always be a bad power supply. replacement power supply was cheap like 20$ from ebay. but still i get not even... -
I bought this p2210f dell monitor to fix. Schematic is the same as p2210.
Behaviour is that monitors comes on but then backlight switches off almost instantly. If I look with flashlight I can still find the "No signal message". So definitely a backlight issue. Trying to advance the issue I proved that the protection circuit is switching off the backlight by shorting out C3 and resistor to disable the INL chip then re enable by removing the short.
This is where it gets interesting. When I disassembled the monitor to solder leads on c3 capacitor I noticed the backlight flickered... -
Hello all,
Am trying to figure out this backlight issue with this A1990 Macbook Pro.
Tests performed:
There is no backlight even with a good screen.
Backlight IC is receiving the correct support voltages.
Fuse F8400 ok
Current sense resistor R8400 ok
Backlight IC is receiving 3.3V on enable pin.
Backlight IC receiving voltage from PPBUS_G3H, aprox 12.5V.
Backlight IC receiving 5V from PP5V_G3S
Backlight IC BKLT_SCL and BKLT_SDA both measure 0.545V diode mode to ground
I2C_BKLT_SCL and I2C_BKLT_SDA both measure... -
Hello, got an iPad Pro A2378 12.9 5th gen with no backlight. Got another test unit without screen, tested the screen, still no backlight with the test unit.
Figured out the backlight on the screen was bad, ordred a new backlight from mobilesentrix, *carefully replaced it* without damaging the lcd, oh well.
Final result, issue is still there, the screen has no back lights. So i'm back to square one, with 3 hours less and 100$ out, issue still on the screen.
The panel is still ok, i can see the apple in the middle of the screen when it kicks in, just no backlight.
Anyone... -
Hi all,
I've got an LG Flatron 24EN33TA with a backlight issue. The problem began with the monitor not powering up after sitting for a long time (overnight or during the day throughout work). When I would wake the computer up, the backlight would flick on for a second then go out. Sometimes it would take many tries to get it to come on. Once the monitor came on, it worked flawlessly until another long duration of being powered off.
I thought the problem would be bad caps but I checked both of the caps on the board and they are fine. I also tried powering the monitor from...
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