Macbook Air A1466 820-00165-A Backlight

[m4a2t0t]

Backlight not functioning. Fuse was blown, replaced and still no backlight.

Does anyone have the board viewer for this one? I have the pdf schematics but I don't see the LVDS connector anywhere and I have no clue where these SMDs are on the board. IIRC the last 3 or so pins are for the backlight, they are at 0V.

It looks like it was liquid damaged. Look at pics of the backside of board with the buildup. I cleaned up that chip a little more and can see the pins again but it still looks nasty.

I took some voltage measurements on the top side of the board (last pic), not even sure if that's all for the BL circuit or not.

Thanks for any help.

[gabik111]

Re: Macbook Air A1466 820-00165-A Backlight

Did you check the fuse after replacing it and restart laptop? It might be blown again. I'm fighting with the same problem in 2012 Macbook Pro.

[kiraro]

Re: Macbook Air A1466 820-00165-A Backlight

Hi, according to this topic :

https://www.rossmanngroup.com/boards...6-no-backlight

The j113 model have the same backlight parts that would help you ,read the topic that will help you to limit the problem cause(LCD/bad connector/circuit) .
I attached here the link for schematic and boardview for j113.

Link:

https://drive.google.com/file/d/0Bz0...5zdEp1b1U/view

I hope that help you .

[BlueMidnight]

Re: Macbook Air A1466 820-00165-A Backlight

There appears to be a problem in/around U7701. PPBUS_G3H is supposed to be 8.6V, and it is. But U7701 is supposed to cycle an internal FET to generate a higher voltage on the inductor L7701, which then passes through the diode D7701. You are reading 8.6V the whole way through.

Make sure the inputs to U7701 look good. (e.g. the EN pin is high, there's voltage on FB and SW_x pins, etc). If it all looks good, then U7701 is probably bad.

[Magnusa2]

Re: Macbook Air A1466 820-00165-A Backlight

hi here

[m4a2t0t]

Re: Macbook Air A1466 820-00165-A Backlight

Thanks all for the responses.

I did recheck the fuse and it is good.

BKL_EN is 2.86 . This appears not correct. 8.59V*100K/(100k+200k) = 5.72v. If I calculated the voltage divider properly. Vout=Vin*R2/(R1+R2) for voltage divider? Should I pull the resistors and check them out of circuit? Incircuit r1 was 70K. R2 I could get a slow build up to 170K and if I removed a probe and checked again it would show 600K.

PPVIN_S0SW_LCDBKLT is 8.59

PPVOUT_SW_LCDBKLT_FB is 8.54. I cant find XW7220 but it looks like the test pad is in the right place and that's where I tested.

[m4a2t0t]

Re: Macbook Air A1466 820-00165-A Backlight

I think I miscalculated. If I test the voltage drop across each resistor I get 5.61 for the first and 2.65 for the second. When I calculate each one manually It shows I should get 5.72 and 2.86

Where can I buy the LP8850 from? Is there another part number for it? I can't find it anywhere.

[BlueMidnight]

Re: Macbook Air A1466 820-00165-A Backlight

Yes, it was just a little mix-up. Those new values are correct.

You can find another LP8550 on AliExpress, eBay, Amazon, etc. But it's LP8550 and not LP8850. Just in case you were searching for the wrong thing accidentally :P

[m4a2t0t]

Re: Macbook Air A1466 820-00165-A Backlight

I was wondering why I couldn't find anything.

[Fabbrone]

Re: Macbook Air A1466 820-00165-A Backlight

hello I have a macbook air soo much that after a fall the panel is intact but there is no backlight with a flashlight you see. I checked the fuse is intact and on it there is a voltage of 7.2V. it's correct ?

[simplylcd]

Re: Macbook Air A1466 820-00165-A Backlight

Did you resolve the issue , I have a 820-3662 with a back light issue the voltages on u7701 are as follows.

u7701 / 1=0 / 2=0 / 3=0 / 4=0 / 5=5 / 6=5 / 7=0 / 8=5 / 9=12.5 / 10 = 12.5 / 11 = 12.4 / 12 = 0 / 13 = 0.1 / 14 =0.1 / 15 = 4.7 / 16 = 4.7 / 17 = 3.3 / 18 = 5 / 19 = 0 / 20 =0 / 21 =0 / 22 = 0 / 23 =0 / 24 = 0 - screen connected / no keyboard/track-pad connected