A1466 with no backlight but boots (820-00165)

[mon2]

Hi. Having some fun with a 820-00165 logic board (liquid damaged) that is booting (no ssd installed) but is missing a backlight.

Corrosion near D7701 and nearby inductor / caps for the backlight area. Cleaned up with alcohol but always see 8v5 for the backlight.

Replaced the TI LP8550 3 times and each time, was dancing yet no high LED voltage @ cathode of D7701.

Came across the logiwiki page for the A1466 and the details of the via that is on the same side is gold. This tiny via corroded away and no longer supplied the feedback voltage to ball A5 of the LP8550. After many attempts to solder a bridge to D7701, ended up using a single strand of wire from an old IDE cable and gently inserted to the corner A5 ball.

Then bridged to the bottom side vias that offer the same rail.

This worked! Now have 23v9 volts (PPHV_S0SW_LCDBKLT) on the cathode of D7701 -> same voltage on the LVDS cable (pins 3 & 4). All good.

Except LCD panel is still dark. Tested with another LCD panel - same issue and remains dark.

Using a flashlight on the back of the display, can see the flashing folder (since SSD is not installed). Have fan spin.

Diode values for

R7717, R7718, R7719, R7720, R7721 @ 0v6 = matches the boardview values
R7722 = 0v4 ; could this be an issue ??

Any ideas on what could be wrong here?

Perhaps reflow U7701 again ?

[mon2]

Re: A1466 with no backlight but boots (820-00165)

Update - removed the LCD and found 5v0 @ R7722 only.

Suspecting that this is (was) due to a short under the LP8550. Reflowed the IC again and made it do the wah-watusi. So much fun while trying to retain the single strand of wire @ A5 to complete the FB circuit. Keep this exercise in mind for a night with the wife & kids.

Now lost the 25v boost but R7722 is like the other LED return lines with diode reading @ 0v6.

Will replace this dreaded IC tomorrow when rested.

[ACS-Repair]

Re: A1466 with no backlight but boots (820-00165)

I had this once on an older MacBook Air, maybe 2012 model. I also had 24 volts on the backlight but it was not enough for the backlight to be visible. I found with the help of others that I could get full brightness simply by doing a PRAM reset. The screen immediately brightened up. Unfortunately, I think you had this working but now you have a new problem to resolve first. I also did a hair wire to pin A5 on the LED backlight driver (00165) and it was tricky to apply without touching other pins. I think you're almost there.