backlight does not work after lcd disconnect

Question

iPad 2

Wi-Fi, GSMとCDMA モデルのiPad第二世代です。あるモデルはiPad3発売前に改良されたものがあります。修理は困難で、熱で温めてこじ開ける作業が必須です。

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rspaargaren @rspaargaren

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投稿日: 2017年9月24日

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backlight does not work after lcd disconnect

I have disconnected the LCD without disconnection it from the battery....stupid. But OK now I have the common problem of not having a backlight.

I have had this problem before a year ago but then it came up "by it self" after a while.

What id did so far without result:

- power off/on

- reset settings

- hard reset

- disconnect from battery for a night

- checked connection of ribbon cable

- Replace the filter and the coil.

Before replacing the filter and coil I already had a voltage level of approx. 3.8V at the backlight pins / outlet of filter. So my guess was replacement of filter / coil should not be required. But I did anyhow but without result. Still after replacing I have a voltage level of 3.8 after filter, diode, coil and before the coil. I did not replace the diode as it is blokking in one direction and "open" in the other.

So there is no 18V available... So what else can I do, besides using the Ipad as an advanced cutting board?

I

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Minho @refectio

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投稿日: 2017年9月24日

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The backlight IC (PMIC) is probably damaged. It's purpose is to drive a modulated square wave (PWM) to adjust the boost the voltage. It is in effect, a boost converter. So if the voltage is not boosting and you've already changed the coil, the diode appears good and the filter is fine, then change the IC.

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You should comment on the answer so that a notification is sent. I just caught this by chance.

I agree, it's hard finding the PMIC. Do you have any donor boards?

Minho さんによる2017年9月24日

REPOST Now in the correct field... Is there a way to test the main backlight-Ic? As changing that part Will not be easy and a replacement is hard to get. It would probably mean the iPad is scrap or replacing the complete main board...? Anybody an idea?

rspaargaren さんによる2017年9月24日

No I do not have a donor board, i could start looking for it but then I still have the question mark ?

1. whether this IC is really the cause.

2. Replacement of the IC is above my skills. (I have got hot air gun, etc)

I like a challenge but I would like to know whether there is any change of a positive outcome of the repair...

rspaargaren さんによる2017年9月24日

You know, it could possibly be a damaged LCD.

Unfortunately, these IC's are mainly black boxes because we don't know the full logic inside them (proprietary designs). That said, this IC's job, at least for the backlight, is to modulate an output signal to drive the coil. If you are confident that the coil, diode and downstream filter (L2200) are working properly, then replacing the IC is the next step. Sadly, there are never any guarantees.

At any rate, you are not properly equipped to do this yourself. A hot air gun will do more damage than it fixes. If you still want this repaired, you could ask a local shop to try an LCD (if they have one in stock) to eliminate that possibility. Then look for a micro-soldering repair shop for a proper diagnosis and estimate. You'll need to decide if the cost is worth it.

Minho さんによる2017年9月25日

The only thing I did not replace was the diode but I will give that a try... Related to the LCD my guess it is working OK. since I am measuring the voltage level with and without the lcd connected. So if I don't have 18v the led will not fire. If it comes to replacing the IC, I don't think I will go that step for this relatively old iPad.

rspaargaren さんによる2017年9月26日

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You should comment on the answer so that a notification is sent. I just caught this by chance.

I agree, it's hard finding the PMIC. Do you have any donor boards? — Minho
REPOST Now in the correct field... Is there a way to test the main backlight-Ic? As changing that part Will not be easy and a replacement is hard to get. It would probably mean the iPad is scrap or replacing the complete main board...? Anybody an idea? — rspaargaren
No I do not have a donor board, i could start looking for it but then I still have the question mark ?

1. whether this IC is really the cause.

2. Replacement of the IC is above my skills. (I have got hot air gun, etc)

I like a challenge but I would like to know whether there is any change of a positive outcome of the repair... — rspaargaren
You know, it could possibly be a damaged LCD.

Unfortunately, these IC's are mainly black boxes because we don't know the full logic inside them (proprietary designs). That said, this IC's job, at least for the backlight, is to modulate an output signal to drive the coil. If you are confident that the coil, diode and downstream filter (L2200) are working properly, then replacing the IC is the next step. Sadly, there are never any guarantees.

At any rate, you are not properly equipped to do this yourself. A hot air gun will do more damage than it fixes. If you still want this repaired, you could ask a local shop to try an LCD (if they have one in stock) to eliminate that possibility. Then look for a micro-soldering repair shop for a proper diagnosis and estimate. You'll need to decide if the cost is worth it. — Minho
The only thing I did not replace was the diode but I will give that a try... Related to the LCD my guess it is working OK. since I am measuring the voltage level with and without the lcd connected. So if I don't have 18v the led will not fire. If it comes to replacing the IC, I don't think I will go that step for this relatively old iPad. — rspaargaren

iPad 2

backlight does not work after lcd disconnect

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