No Backlight & Image present - iMac (21.5-inch, Late 2012), 820-3302A

Hey everyone!

I have some experience repairing Macbooks but would like some of your input regarding this iMac repair. It’s a Late 2012 model that boots fine and is stable on an external screen. However, while an image is present on the lcd, no backlight shows up.

I have proceeded to open the device and no component seems to be physically broken in the backlight area.

By measuring some test points I noticed that no current is present along the J9700 backlight connector so I’m fairly certain that it is not a display assembly issue.

Following the schematic, I found that the fuse F9700 is continuous and provides the 12V correctly to R9712 and then FB9708, meaning that Q9702 receives 12V on pins 1, 2, 3.

However, perhaps most interestingly, nothing is present on pin 5 regarding PP12V_S0_BKLT_PWR and I’m assuming this is why the rest of the circuit near J9700 gets no power.

To summarize:

F9700 = 12v pin 1 and 2

R9712 = 12v pin 1 and 2

FB9708 = 12v pin 1 and 2

Q9702

Pins 1, 2, and 3 = 12v

Pin 4 = 11.75

Pin 5 = 0v

Any help or tips would be really appreciated :)