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What exactly are the backlight filters for & repercusions of jumping?

What exactly are the backlight filters for & repercussions of jumping?

I want to fully understand the reasoning, cannot find an answer on the web apart from people saying you can jump all filters when blown or missing in a phone!!

Apple didn't just pay and install them for fun, but I know from experience you can jump them when you haven't a replacement available.

So my understanding of the backlight filter or more accurately the ferrite beads is that ferrite beads are to stop unwanted frequencies, as far as I know ferrite beads are low pass so block high frequency.

But what are they blocking, the Rf output of the phone, the clock signals from the cpu or other parts parts of the motherboard or from external interference like another phones transmissions?

Why then if you use a jumper then does it appear to have no affect on the backlight or in other parts if the board when you jump them?

The fact they blow when a short happens on the line, is that co-incidence or was it planned by the designers knowing they can only take 200ma for example.

Cheers - Simon.

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There is a reason why fuses are rated at a certain amount and used in phones. This is because you don't want a overkill fuse that allows a large amount of current / power going in and burning out other components past it instead of the fuse.

It's best that the fuse blows out first and not go through and burn out the other components just because the fuse was rated for a way higher load while the other components past that fuse weren't.

Correct me if I'm wrong but I think this was an intentional decision and I think it is a good one too.

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The way you're talking about it, I think the backlight filters are inductors that are there to prevent radiofrequncy interference from the boost converter that increases the voltage to the backlight. That circuit needs to turn on and off really fast, at the same frequencies as some radio bands. Thus, these filters help to prevent the backlight cable from becoming an antenna and interfering with other stuff. In all likelihood, if you don't care about compliance, and as long as your phone works fine, bridging it shouldn't create too many issues.

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simon will be eternally grateful.
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