First time caller, long time listener! So, here's an ADC with a LED backlight issue that I got for cheap recently. It uses an LM240WU6-SDA1 LCD from LG.
Symptom:
Upon first powering on, backlight flashes on once for such a short duration that it's almost undetectable, but it does happen. After that, the display is dark. Unplugging/replugging the displayport connector does not cause the flash to reoccur, but cycling the power to the display does.
What I've done:
The LCD itself displays fine, determined via a flashlight test.
Visually inspected for any blown or burnt components.
As per the Apple Technician Guide for the display, I've checked the voltages at test points on the logic board for all the major functions, which checked out. (24.7V for points labeled as 24.5V, 12.15V for 12V points, 3.35V for 3.3V points and 1.03V for 1V points)
Checked continuity across all lanes on the LCD function cable.
Checked continuity across fuses on LCD PCB.
Additional Information:
On eBay I've seen quite a few used but working logic boards and PSUs "pulled from units with bad LCDs".
In reports of problems with these displays on other sites, people who took them in to Apple said the LCD and sometimes the logic board was replaced.
A similar LG LCD panel (Same model number except for the SDA1 suffix) that is used in iMacs suffers from LEDs not functioning, with the solution being to push on the lower left corner.
The technician guide can be found here: https://cdn.badcaps-static.com/pdfs/...e111828a87.pdf
All this information leads me to believe that the issue lies in the LCD panel itself, however, I wanted to get some input on other things I could check out. If the problem is with the panel, I'd like to try and fix that, too. There isn't a whole lot of info to be found on repairing LED backlit displays, but I have it and might as well try; might learn something!
Thanks in advance, guys.
Images:
1, 2: Logic Board
3, 4: Power Supply
5, 6, 7, 8: LCD PCB with arrows pointing to fuses
9: LED Driver cable. I couldn't test to see if it was lose while the display was on and connected, and I can't test for continuity without disassembling the panel. Could it be the problem?
10: Panel label
Symptom:
Upon first powering on, backlight flashes on once for such a short duration that it's almost undetectable, but it does happen. After that, the display is dark. Unplugging/replugging the displayport connector does not cause the flash to reoccur, but cycling the power to the display does.
What I've done:
The LCD itself displays fine, determined via a flashlight test.
Visually inspected for any blown or burnt components.
As per the Apple Technician Guide for the display, I've checked the voltages at test points on the logic board for all the major functions, which checked out. (24.7V for points labeled as 24.5V, 12.15V for 12V points, 3.35V for 3.3V points and 1.03V for 1V points)
Checked continuity across all lanes on the LCD function cable.
Checked continuity across fuses on LCD PCB.
Additional Information:
On eBay I've seen quite a few used but working logic boards and PSUs "pulled from units with bad LCDs".
In reports of problems with these displays on other sites, people who took them in to Apple said the LCD and sometimes the logic board was replaced.
A similar LG LCD panel (Same model number except for the SDA1 suffix) that is used in iMacs suffers from LEDs not functioning, with the solution being to push on the lower left corner.
The technician guide can be found here: https://cdn.badcaps-static.com/pdfs/...e111828a87.pdf
All this information leads me to believe that the issue lies in the LCD panel itself, however, I wanted to get some input on other things I could check out. If the problem is with the panel, I'd like to try and fix that, too. There isn't a whole lot of info to be found on repairing LED backlit displays, but I have it and might as well try; might learn something!
Thanks in advance, guys.
Images:
1, 2: Logic Board
3, 4: Power Supply
5, 6, 7, 8: LCD PCB with arrows pointing to fuses
9: LED Driver cable. I couldn't test to see if it was lose while the display was on and connected, and I can't test for continuity without disassembling the panel. Could it be the problem?
10: Panel label
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