820-3330-B A1286 Image, No Backlight

[diesel1024]

Hey guys,

Looking for a bit of advice here, I'm very new board repair specifically. Randomly the backlight stopped working on my Mid 2012 15" MBP 2.3 Unibody. Had left it for a few hours and came back to the backlight no longer working. To note, I keep the bottom panel unscrewed due to the ram slot issues, so it is a very small possibility something could've gotten nicked. I measured some voltages, so here's what I got:

10.71V on both sides of F9700 (PPBUS_G3H) & (PPBUS_S0_LCDBKLT_FUSED)
Continuity to R9788 & C9782
Q9707 only thing that looked even a bit damaged (https://imgur.com/a/lLBdXvs)
Pin 2 - 3.28 (LCD_BKLT_EN)
Pin 5 - 3.26 (BKLT_PLT_RST_L)
0V on 38-40 of J9000 (PPVOUT_S0_LCDBKLT)

Hoping this can get me somewhere to look next, already tried multiple SMC and PRAM resets

I have at least one spare parts board too, so I theoretically could swap things to an extent.

[mon2]

Re: 820-3330-B A1286 Image, No Backlight

Not at my desk but is the nicked part linked to the lcd backlight? Was this part nicked before or after losing the backlight

[diesel1024]

Re: 820-3330-B A1286 Image, No Backlight

I unfortunately do not know if it was nicked before or after, all I know is it is currently nicked. It looks to be linked to the lcd backlight in some ways. From what I can tell it looks like it controls the enabling and disabling of the backlight based on the trace/pin names.

[mon2]

Re: 820-3330-B A1286 Image, No Backlight

See attached. The nicked mosfet is a voltage divider enabler mosfet.

When ON, the ground connection mates onto R9789 to allow for the common junction between R9789 & R9788 to build a voltage divider.

If the nicked mosfet is ON (for both sections as there are 2 in a single package), then the GATE voltage of Q9706 will be LOWER than the voltage being passed between the source / drain pins of Q9706.

Mosfets are like solid state switches / relays. The mosfet @ Q9706 is a P-channel mosfet. So this mosfet will enable only if the gate voltage is LOWER than the source / drain pins.

Carefully measure the voltage to ground readings of the Q9706 mosfet.

Interested in the SOURCE, DRAIN and GATE pin voltages.

If the GATE voltage is the same as the voltage seen on pin # 4 of Q9706, then this mosfet is OFF since the voltage divider is not active.

Confirm and post the measurements.

[diesel1024]

Re: 820-3330-B A1286 Image, No Backlight

I haven't had a chance to get those measurements, but I looked back at the board today, and comparing it to a 2011 2.4 i7 board (820-2915) I noticed a component next to Q9707 was actually completely missing, and according to this diagram, it looks like that is a point which LCDBKLT_EN_DIV goes through to LCDBKLT_EN_L. I'm going to try to replace the cap/resistor, whatever it may be and see if that fixes it. My donor 820-2530 has two of these:

147K
1%
1/16W MF-LF
402

Will update.

[diesel1024]

Re: 820-3330-B A1286 Image, No Backlight

Update, added some solder to the pads where the missing component was, took R7408 from 820-2530, soldered it to the pads on my 820-3330-B, it isn't pretty, but to my amazement, I now have backlight, so from what I can tell Q9707 is fine besides having that cosmetic damage. Now only time will tell if it'll last.

Thank you for your help mon2!

[diesel1024]

Re: 820-3330-B A1286 Image, No Backlight

photos

[mon2]

Re: 820-3330-B A1286 Image, No Backlight

Well done and thanks for the updates.