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Charging Circuit Failure (Gas Gauge), Micro Solder help

During a battery swap on my old iPhone 8 I damaged some of the soldered-on components nearby the data connector for the battery. Now the iphone battery won’t charge, and the device will only stay on for a few seconds before rebooting. Most users on the forum came to the conclusion that this was a damaged charging circuit/data input for the battery.

Now almost a year has gone by, I have a new phone and a lot more free time and I thought to myself, this seems to be a great little project to get me into micro soldering, something I’ve wanted to do for a while. I’ve been watching some tutorials regarding this issue specifically, and I wanted to ask you all if I have the right idea or am completely lost.

Lets begin,

So here is an image of the phoneboard view of the circuit at hand:

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the area circled in blue represents the components which have fallen off the board thanks to my aggressive connector attaching. I’d assume these are just resistors but I honestly don’t know (if anyone would like to tell me I’d love to hear), and the one on the right connects to the top right 3 prong component (MOSFET maybe?), and then connects to the main processor (not shown in photo). My thought process, was to solder a short wire (represented in red) between those two terminals. Would this work, or am I completely in the wrong?

Also here is the photo of the board through my microscope:

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Just wanted to write a follow up for those in a similar situation as myself,

I went with Chris’s approach (thanks Chris), initially I purchased a pack of these resistors from digikey (link). Later Chris recommended just using a resistor from another IC locked/dead iPhone 8 board so I found a dead board on eBay and also ordered it.

Before you even get started attempting this, I will warn you, these resistors are absurdly tiny, the naked eye will be unable to see them, they are smaller than a spec of dust, moral of the story, be very careful when handling and moving them.

I won’t go into much depth on the equipment used, I found a cheap digital microscope on amazon along with lead based solder, wick, and flux. I also found some nice standard soldering iron tips with very fine points on eBay (which you will definitely need, the scale of these things is less than a human hair).

Once all my parts arrived I began the repair, I was able to remove the resistor from the dead iPhone board, however I accidentally lost it while moving it to the phone I was repairing… whoops. So I decided I’ll just give the resistors off digi-key a try, they are technically thick film and not metal film as originally used however they appear to work fine. Phone appears to be completely functional after soldering that new resistor on (crazy how important something smaller than a hair can be).

TLDR:

You can use thick film resistors over metal oxide resistors if unable to get a resistor from a donor board. Be patient during the process and steady, these parts are extremely tiny. Only the resistor needs to be replaced, the capacitor is unnecessary!

Thanks again to those who helped me through this process, this was a very fun little microsoldering project and now I can repurpose a once useless phone!

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There is no reason to run a jumper wire. Just replace that resistor and be careful not to nudge the diode above it. The component to the left that is missing is a capacitor and the phone should operate normal without it. The value of the resistor is 33.5% 1/32W MF 01005

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I saw your comment on another thread when I was looking for the specs of the R3201 cause I was considering buying some lol. I'll just order some and try it out, thanks!

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does MF stand for metal film resistors? I can't find any metal film resistors with these specs on digikey, although there is thick film

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@Brandon Egger Yes MF is metal film. Thick film resistors might be too noisy. I usually source mine from donner boards. It might pay to purchase a cheap iCloud locked board at least you will have extra parts in case something else gets damaged while doing the repair. Its strange mouser hasn’t got any.

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Have you been able to “buzz out” the pads with a multimeter to see if they’re electrically connected?

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Unfortunately no, my multimeter probes are too large to be of any use at this scale. Is there a multimeter you recommend for checking continuity with such tiny components?

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