Backlight gone; cannot find backlight IC chip

Question

MacBook Air 11インチ Early 2015

2015年3月のアップデートではAppleの11インチMacBook Airは第5世代Intel Core i5またはi7プロセッサーを特徴としており、これによりわずかな性能とバッテリーライフの向上がされました。

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Falcon 16 @falcon16

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投稿日: 5日前2026年1月2日

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Backlight gone; cannot find backlight IC chip

I've a A1465 macbook air, and it's a custom board. This has introduced some head-scratching when the backlight suddenly stopped working. No drops or spills. I looked at all of the online resources I could find, like board schematics, and none of them were able to provide the location of the backlight chip, or the fuses etc. Might you please highlight where the IC chip is, and its part number, so I can replace it. Same for the fuse. Any further advice would be appreciated!

Edit (05/01/2026):

The board is not custom, and is 820-3435-B. Voltage to the backlight fuse is 6.8V.

Below are photos of the region around the display cable, and nearby chips, and further photos of the overall board.

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Picture 1 above the connector is a fuse (orange) with a 'P' in it, I believe this is the BL fuse....

livfe さんによる5日前2026年1月3日

@livfe

Thanks for that! I'll check the conductivity of it this evening. My question is, if that is the source, and it's blown, what is the actual fuse as I'll need to get a replacement one. Do you know what the fuse is called?

Falcon 16 さんによる5日前2026年1月3日

@falcon16 F7700 I believe @oldturkey03

livfe さんによる5日前2026年1月3日

@livfe

It seems that the fuse is fine. I checked the resistance and it's 0.04 ohms.

Must be the backlight chip. I thought it would be as there was no reason for the fuse to blow. But thanks! Any suggestions?

Falcon 16 さんによる5日前2026年1月3日

@falcon16 I have encountered this a few times before and for me was always this fuse. Calling@danj @oldturkey03 they may have another idea.

livfe さんによる5日前2026年1月3日

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Picture 1 above the connector is a fuse (orange) with a 'P' in it, I believe this is the BL fuse.... — livfe
@livfe

Thanks for that! I'll check the conductivity of it this evening. My question is, if that is the source, and it's blown, what is the actual fuse as I'll need to get a replacement one. Do you know what the fuse is called? — Falcon 16
@livfe

It seems that the fuse is fine. I checked the resistance and it's 0.04 ohms.

Must be the backlight chip. I thought it would be as there was no reason for the fuse to blow. But thanks! Any suggestions? — Falcon 16
@falcon16 I have encountered this a few times before and for me was always this fuse. Calling@danj @oldturkey03 they may have another idea. — livfe

Alisha C @flannelist 評価: 41.6千 28 48 40 · Answer 1 · 2026-01-03T04:06:33-07:00

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Alisha C @flannelist

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投稿日: 5日前2026年1月3日

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Backlight driver is this one right here.

It's a Texas Instruments LP8550 backlight driver. But I would check for shorts on anything that comes out of that chip

The fuse is the one here with the P on it. Although in my experience, the fuse is generally not the issue. It's more likely to be a bad capacitor, or the backlight driver itself if the board is the issue (rather than the display or the cable).

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@flannelist

Thanks! I'll keep that in mind in case it does turn out to be the backlight IC. I tested the conductivity of the fuse, and it's all right.

When I look up "LP8550", chips come up, all right, but they have different writing on them. Is there a particular identifier I need or are they all the same, and if so, why are they labelled differently?

Thanks again!

Falcon 16 さんによる3日前2026年1月4日

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oldturkey03 @oldturkey03 評価: 838.6千 1.3千 943 2.4千 · Answer 2 · 2026-01-03T06:07:12-07:00

oldturkey03 @oldturkey03

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@falcon16 I would not worry to much about measuring resistance on the fuse but measure for continuity, and most importantly measure for any voltage. You know, multimeter in VDC mode (somewhere in the 30V range) Black probe to ground and red probe to the contacts of the fuse. What makes this "it's a custom board"? What is the 820-xxxx number on your board? Also, check the voltage on L7701 That is one of those inductors that likes to fail :-) That is the grey square looking component that has the numbers 150 408 printed on it.

That voltage itself will give you a pretty good idea about what is going on with your backlight. If the backlight is ~45V or more that means there is no load on the backlight circuit. That may be because of the screen or the display cable/connector. If the backlight voltage is 25V-40V then the boost circuit is working and the no backlight issue could again be a connector, cable, and LCD issue. If the backlight is PPBus voltage your boost circuit isn't working. Check the feedback trace, LCD driver, and make sure that your backlight enable gets power. Finally, if the backlight voltage is 0V, check for a short by working your way back to the PPBUS_S0_LCDBKLT circuit

@falcon16 one of the important part of why we like to have pictures of the complete boards and well focused. It'll help identifying things. Here is an example of where to find the 820-xxxx board number

Pin 3 of U7701 is the BKL_EN pin. Since it is a BGA IC (can't reach the solder balls :-) you would need to measure the voltage on either R7731 and R7115 (measure on the ends where the arrows point to. The opposite end is ground). Those are the same resistors that are a common failure issue. Make sure that those are ok. R7731 is a 200K resistor and R7715 is a 100K resistor.

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Where would I find the board number? I was just told by the seller on eBay that it was a custom job by Apple. Where is the inductor; I cannot see it in any of the pictures? Might they be one of the ones covered in glue?

Also, when testing the voltage, where is the PPBUS pin and how can I work along it?

Cheers!

Falcon 16 さんによる3日前2026年1月4日

@oldturkey03 I found the board number by happy chance! It's a 820-3435-B!

The voltage on the fuse was 5-6v.

Falcon 16 さんによる3日前2026年1月4日

@falcon16 yup, standard board for this MBA. Double check the voltage (VDC) The voltage is definitely not high enough to get your backlight to work. It should show somewhere in the 12VDC to 12.6VDC range on the fuse

oldturkey03 さんによる3日前2026年1月4日

@falcon16 PPBUS is not a pin but a circuit. You'd be looking for the PPBUS_G3H which provides the voltage to the backlight circuitry.

oldturkey03 さんによる3日前2026年1月4日

@oldturkey03

Danke sehr! I checked the voltages on both, and it reads a stable 6.8v for both. Sorry about the photos but there is only so much I can do with a phone; I tried my best.

Sooooooooo what might be the issue here? New IC chip?

Falcon 16 さんによる3日前2026年1月4日

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MacBook Air 11インチ Early 2015

Backlight gone; cannot find backlight IC chip

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Update (01/04/26)

Update (01/05/26)

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