I've been reading the thread started by Dadioh on his adventures of repairing the faulty LED backlights on his MacBook. I thought it was going to be just an easy "replace the backlight fuse" issue. However after finishing, and searching through 54 pages of mostly helpful material I'm still having issues even with starting the diagnosis.
My Goal:
Learn more about proper circuit board diagnosis, identifying the actual causes rather than replacing every component without taking any measurements. Doing this through a concrete example of LED backlight issues on a 2010 MacBook (becasue I happen to have this problem..
)
The Specs of the MacBook:
- 2010 MacBook A1342 2.4GHz
- 820-2877-B
Tools and materials I have:
- SCHEM MLB_LDO K87, SCRATCHO, 04/26/2010
- MASTECH MS8268 autorange digital multimeter
The Symptoms:
It was not direct water damage, but the computer was mostly kept in the trunk of an old car (I know, I know).
The MacBook turned on, but there was no backlight on the screen (with a flashlight there was image), and the battery was not charging. Besides this the computer is perfectly usable.
The Progress:
- I managed to reset the SMC by removing the battery and holding the power button for 15 sec. This solved the problem of the battery, which charges now.
- After closely examining of the logic board, I noticed signs of corrosion mostly around the power and the LVDS connector pin.
- The 18th &19th pin on the LVDS connector were black and completely dissolved and when I cleaned them, they completely disappeared (attached image)
- I found the 2A fuse for the Backlight circuit, I checked it for continuity, it is fine, the fuse is closed.
- After following the schematics I concluded I should be able to measure some voltage on the board under the 18th & 19th pin, but there was 0V.
- So I thought I'd measure the resistors around the WLED Driver, but my values are off from the schematics (the R9717-R9722 resistors showed 0 ohm, and I found 2 other that showd 4Mohm!)
- I gave up and measured Voltage across the 2A backlight fuse and it is 0V!
I know I'm just running around, but I have little experience in diagnosing circuit board problems properly, yet
And this is where I am stuck now, because I know that the input voltage should come from "PPBUS_S0_LCDBKLT_PWR" to the fuse, but where is that on the board? I cannot figure it out from the schematics I have.
How do we go about diagnosing the issue properly and understanding the schematics?
How do we know from the schematics where a component is exactly located on the board?
My Goal:
Learn more about proper circuit board diagnosis, identifying the actual causes rather than replacing every component without taking any measurements. Doing this through a concrete example of LED backlight issues on a 2010 MacBook (becasue I happen to have this problem..
)The Specs of the MacBook:
- 2010 MacBook A1342 2.4GHz
- 820-2877-B
Tools and materials I have:
- SCHEM MLB_LDO K87, SCRATCHO, 04/26/2010
- MASTECH MS8268 autorange digital multimeter
The Symptoms:
It was not direct water damage, but the computer was mostly kept in the trunk of an old car (I know, I know
).The MacBook turned on, but there was no backlight on the screen (with a flashlight there was image), and the battery was not charging. Besides this the computer is perfectly usable.
The Progress:
- I managed to reset the SMC by removing the battery and holding the power button for 15 sec. This solved the problem of the battery, which charges now.
- After closely examining of the logic board, I noticed signs of corrosion mostly around the power and the LVDS connector pin.
- The 18th &19th pin on the LVDS connector were black and completely dissolved and when I cleaned them, they completely disappeared (attached image)
- I found the 2A fuse for the Backlight circuit, I checked it for continuity, it is fine, the fuse is closed.
- After following the schematics I concluded I should be able to measure some voltage on the board under the 18th & 19th pin, but there was 0V.
- So I thought I'd measure the resistors around the WLED Driver, but my values are off from the schematics (the R9717-R9722 resistors showed 0 ohm, and I found 2 other that showd 4Mohm!)
- I gave up and measured Voltage across the 2A backlight fuse and it is 0V!
I know I'm just running around, but I have little experience in diagnosing circuit board problems properly, yet
And this is where I am stuck now, because I know that the input voltage should come from "PPBUS_S0_LCDBKLT_PWR" to the fuse, but where is that on the board? I cannot figure it out from the schematics I have.
How do we go about diagnosing the issue properly and understanding the schematics?
How do we know from the schematics where a component is exactly located on the board?
