Received a MacBook A2337 with no backlight issue.
Model Number: A2337
Year released: Late 2020
Defect Phenomenon
The MacBook has been repaired by another repair shop and can boot up normally, but the backlight does not work.
Troubleshooting
Disassemble the MacBook, and first, we find some shielding covers are missing.
(The shielding covers are not easy to source from online trade platforms or on the market, it would be a little headache… Forming a good repair habit is really important for both the repair shop’s reputation and the customer’s basic benefit. )
Then boot the MacBook and check carefully, we can see the Apple logo, but it’s very dim
Then let’s take out the motherboard and measure the diode value around the backlight IC.
After measuring, all the diode values around the backlight IC are normal.
Then connect with the DC power supply machine to measure the voltage values.
After measuring, find the 5V backlight input power cannot be measured.
As we can see from the simplified block diagram, the 5V voltage is sent out from UV300 to the backlight IC UP800. So there are two possibilities that might cause the 5V voltage cannot be generated
- UC300 working conditions are not satisfied
- UC300 itself with problem
After measuring, the 12V input voltage is OK
So let’s focus on checking the backlight IC UP800 and the UC300
Check the backlight IC under the microscope carefully, the backlight IC has been fixed before, and a lot of solder flux is flowed out from the base of the chip.
And on the other side, a chip also has been repaired before
Continue to check the 5VS2 chip UC300, the chip has not been repaired, but a small resistor around it looks abnormal.
As the arrow marked, this little resistor is related to the ENABLE signal for the UC300.
We push it slightly with the tweezer and it just came off easily, so this might be the reason of no backlight
Repair Process
Replace the little resistor with a new one, then clean the motherboard thoroughly
After that, connect with the DC power supply and measure the 5V voltage for the backlight again.
This time, the 5V voltage for the backlight IC can be measured
Then assemble the MacBook and test it again, the MacBook can display normally. The issue gets resolved by the resistor RC333 replacement.
>> Stay tuned to the REWA Academy to light up your repair skills.
