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La version Wi-Fi de l'iPad Air d'Apple, numéro de modèle A1474. Disponible en gris sidéral ou argent, il emploie le processeur A7 personnalisé et est livré dans des configurations 16, 32, 64 et 128 Go.

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Backlight filters / diodes

I have a question regarding the filters and diodes on an ipad air wi-fi.

This is my first attempt to fix this kind of thing, so bear with me please because i am still trying to learn things.


So, the backlight is sometimes working (barely, left side has 50% “flashlight”) and sometimes isnt at all. (the right side of the screens seems fine)


The damage came from a blown lcd connector that burned filter L7085


If i measure both diodes D8258 and D8228, they read out somewhere around 0.6 or 0.7 (out of my head) and they do not seem cracked or whatsoever.


The filters though, at least one of them (the right one) looked bad, but i changed both of them with used filters from a donor and the backlight started working again on a new lcd, only to have it malfunction again after a few power button standby clicks.


My main question, when i measure backlight filters, do they need continuity or not?

I have always thought they did have to have continuity?

And if it does, does this count for basicly all filters on iphones aswell as ipads?


I am asking this because i bought some brand new filters off a chinese supplier but i get the feeling they didnt send me filters at all but something else. When i measure them they do not have continuity.

What is going on here?

The weird thing is, both filters on the ipad did not have continuity but the backlight still worked for a while, after it stopped working, nothing changed. Though, the filters didnt look blown again but also didnt have continuity. This is why i am so confused!



As a side question.. I did saw that one of the filters (L7085) has a bad/damaged pad/trace on the left side wich barely makes contact.

So just to be sure to have a second option on this; Seeing as L7085 is connected to D8228-K, if i was to make a jumper from L7085 to D8228-K, would this be acceptable?

Or would it be better to make it jump to C8250/1/2/3 or 4?


Thanks in advance!

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Filters are basically like a thin wire that is supposed to blow after a certain amount goes through it like a fuse... so yes they have continuity u may have diodes if they only allow continuity one way.

par

Makes sense. So the "filters" they sent me were probably resistors? I just fchecked for continuity and they didnt have it.

Any idea on if i was to make the jumper if this would be acceptable and safe?

par

I havent got zxw with me or phoneboard, lol in bed eating snickers can check for u in the morning or @refectio may come up with answer before then :)

The filters are supposed to act like fuses and blow to protect the backlight circuit you could just use a blob of solder or a wire in their place to test however it's not recommended as this will usually blow the rest of the circuit if there is a problem in the future...

P.s filters are 0 ohm resistors :)

par

@c9679 ...is that a challenge? :>)

par

@refectio lol I thought u might have zxw memorized by now :) my brain cant retain the names of these things anymore lol

par

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Ferrite Beads (aka filters) are very low resistance (short) in DC. That means when you measure them with a multimeter, they will show 0 Ohms. They become resistive at high frequencies and are really used to filter out high frequency noise.

Take a look at this classic filter. You’ll note that the specs are 240 Ohms of resistance at 100 Mhz and that they can sustain 350mA of current. In DC mode, it will measure 380 mOhms (hence why they appear “short” or have “continuity”.

Don’t order these from Chinese vendors, they are easily accessible via reputable suppliers like DigiKey and Mouser and cost usually just a few pennies.

As for your jumper, both options are good, just select the easier path.

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Never mind my earlier comment...

Yes these will do but you need the 0201 package size.

par

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Kevin sera éternellement reconnaissant.
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