iPhone Decoupling Cap Faulty Replace Or Leave

[SewingYard]

Hi All,

I have just had a look at my sisters iPhone 6 that was water damaged, the phone wouldn't turn on and she needed to get her data off the phone as she didn't back it up ( )

I had a look and found there was a short to ground and removed the shield over the CPU and found that the cap causing it was one of the various decoupling caps, I removed the faulty cap on the top end of the row that apparently is the first one to go in most cases.

The phone booted up and I backed up the data. (sister very happy with her little brother, lol)

Now for my question, the phone appears to be working perfectly without the cap, so do I really need to replace it or will the phone keep running happily without this component, and if that's the case then why was the cap even there in the first place?

Hoping for some easy answers I'm still a beginner in most areas of electronics!

-Wayne

[SpaceCow]

Hi All,

I have just had a look at my sisters iPhone 6 that was water damaged, the phone wouldn't turn on and she needed to get her data off the phone as she didn't back it up ( )

I had a look and found there was a short to ground and removed the shield over the CPU and found that the cap causing it was one of the various decoupling caps, I removed the faulty cap on the top end of the row that apparently is the first one to go in most cases.

The phone booted up and I backed up the data. (sister very happy with her little brother, lol)

Now for my question, the phone appears to be working perfectly without the cap, so do I really need to replace it or will the phone keep running happily without this component, and if that's the case then why was the cap even there in the first place?

Hoping for some easy answers I'm still a beginner in most areas of electronics!

-Wayne

I'm sure someone will post the answer very soon (I am too inexperienced to know), but I wanted to congratulate you on fixing the iPhone. Great job, that was a really nice thing to do for your sister and for the sake of resource conservation.

[Inflex]

The phone booted up and I backed up the data. (sister very happy with her little brother, lol)

Now for my question, the phone appears to be working perfectly without the cap, so do I really need to replace it or will the phone keep running happily without this component, and if that's the case then why was the cap even there in the first place?

Hoping for some easy answers I'm still a beginner in most areas of electronics!

-Wayne

First off, congratulations on the repair, that's a great job you did and most importantly the data is off.

Now, the harder part looms.  Yes, you can just replace the parts but on the back of experience I would be disinclined to invest too much money/time in to it because in many cases there's always something else that'll raise its ugly head in a few more months after these boards have been water damaged (even if you ultrasonic / IPA / kiln as per proper procedure ).  Yes there are many anecdotes of successful recoveries that live on, but there's many more that you don't hear about where it dies a few months later but the person just cans/bins it and moves on to something else.  It's a gamble.

As for why it still works, it's because they're decoupling / ripple-control caps.  Under lighter loads or normal circumstances the design will cope with the loss of a couple of caps and still keep running, however the operational envelope will have been reduced.   Perhaps under a more demanding app and hotter environment and weaker battery the phone will no longer operate reliably without those caps.   When these boards are designed, you usually give yourself a moderate amount of headroom above the worst-case usage scenario;  as such, losing a couple of caps isn't a complete failure.

Congrats again!

[m98]

You've removed only one decoupling cap? Won't change a thing. Decoupling caps are often used redundantly with different values to filter out different frequency components. So the worst case could be that the phone might have slightly higher EM-emissions and that possibly the performance of some analog and RF stuff is slightly reduced, but you won't even notice those effects.

[SL4P]

There's probably more risk of doing more damage by poking around in that tiny space than the benefit of refitting a single cap.
Leave it as-is, and hope it holds out in all other ways.

[SewingYard]

Thanks for all the replies everyone, the input is really appreciated, its good to know what other professionals think and hopefully the responses will be helpful to others in future

Cheers