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Main board not working, all other parts ok after water damage & clean

Tags: #<Tag:0x00007f05e49e3590>

An example of a minor mistake in repair that may have been fatal or may yet prove to be remedied…

My FP2 recently took some light/peripheral water damage (not completely dunked, but a little ingress due to a waterproof pouch leaking), but with very corrosive saltwater! :scream:
After following the iFixit guidelines on repairing water damage:

  • I got the battery out as soon as it was safe to do so, which was after paddling to shore, far too many worrying minutes after the FP2 had hard powered-off itself seconds after I noticed the leak.
  • I dis-assembled the FP2 at home, immersed all parts in alcohol (I used ethanol camp fuel with bitter additive), sloshing it about, gently scrubbed off any visible salt with a toothbrush, and shook off the remaining alcohol.
  • HOWEVER I skipped one mentioned step in that I did not remove all EMI shields, due to the heat-spreader pad that would be damaged by removing it from the main board, and concerns over my own clumsiness. I also didn’t go the full length of dis-assembling the main board from its PC backing, as the available teardown instructions didn’t explain how to do this, so I avoided breaking anything.
  • I dried all parts out over a long period - initially in front of a GPU exhaust fan for a few hours, tested the FP2 after sitting for nearly 24h, it didn’t work, and it’s now been a couple of weeks since then, when I could finally get access to spares to test with.

I was in too much of a rush to take pictures beforehand, but here are the parts after that gentle cleaning:
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2019-09-25-014449 2019-09-25-014458

Now somebody has kindly lent me a FP2 to swap out parts one-by-one so that I could find out what I need to replace if anything.
Despite visible remaining salt stains on the shields of breakout boards, I found to my great dismay that all parts are working(1) except for the main board - I put it together with all known working parts and it didn’t boot up.
That’s the opposite of what I expected to happen and what was predicted by the guide.

I now have access to a food dehydrator away from home, but I think that a couple of weeks is plenty long enough for ambient evaporation to take place.
Having now removed the top shield and ripped the heat spreader to inspect the SMD parts underneath, I saw no signs of corrosion on the top:
2019-10-07-195133 2019-10-07-195203 2019-10-07-195341 2019-10-07-195915 2019-10-07-195933 2019-10-07-200138 2019-10-07-200254 2019-10-07-200422
After removing the main board from its backing (while writing this, and the brown sealing pad around the largest pogo connector pad was easier to remove than I thought - it seems to be a rubber-coated metal block), I saw a tiny bit of salt left by one corner of the bottom (sim-side) shield. I had to be very careful moving the shield from the opposite end first, as that corner was held in place by the dried salt/corrosion.
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According to the aforementioned teardown, the affected component is the one thing I’m most worried about being damaged - the eMMC NAND flash memory from which I want to try and recover recent data. Please lend me your energy!
I’m going to try giving this side of the board some gentle toothbrush & alcohol attention now, then dry it thoroughly again. If that doesn’t work, I’m wondering whether it would be wise to try immersing the main board in ethanol again for a prolonged period to try and remove any remaining trace of salt in there.

I hope that this is a useful lesson for somebody in addition to myself.

(1) I said the modules were “working”, but I meant just enough to boot, charge, show a charging light, buzz and display stuff on the screen. I didn’t test the cameras yet.
Also I already had intermittent issues with the main microphone due to a contact pad on the screen module making poor contact with one grounding spring and being gouged after I found out that squeezing/tapping the bottom-right corner of my FP2 improved the situation short-term. Everyone who likes to listen to music on earphones probably knows about the headphone socket problem too, but that’s a story for another day.

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Interesting report [I am mainly commenting here to make it easier for others to get to the bottom of the first post :slight_smile: ]

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Well, I brushed that salt away with some alcohol. Unfortunately, it looks like I also brushed off a few of the tiny SMD resistors next to that flash memory chip where the solder points were corroded. :grimacing:
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I’ve seen electronics working before (unreliably) when it shouldn’t be, due to a component damaged or missing, but here we’re probably talking about a few open circuits instead of short circuits, not something like dried up capacitors.

What do you think should come next, try and switch it on after it dries tomorrow to see if it sort-of-works, or don’t risk it in case one line was a “cut this to wipe everything” red wire?
Taking bets…
:sleeping_bed:

As far as I recall, alcohol is a very poor solvent for salt, so I doubt it would be very effective. Stove fuel grade ethanol is probably already saturated with salt (amongst other contaminants), so it wouldn’t be my choice for this. You’d probably need deionised water (deionised to avoid issues caused by impurities) to dissolve the salt (deionised water either by itself or mixed with isopropanol). After the water gets rid of the salt, the water then needs to be removed in a way that minimises corrosion when oxygen is added (i.e. during drying). This is often done using isopropanol, as used in the ifixit guide, to displace the water as (amongst other things) it dries much faster.

This is my own understanding - I could be wrong. If in doubt, seek professional assistance and ignore the ramblings of random strangers on the internet.

Obviously, no amount of cleaning will fix damage resulting from short-circuits when the device was on, so you can still be out of luck. I can’t really comment on the mechanical damage you mention.

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You are welcome to read my ramblings as a random stranger, with a similar problem, but lacking the salt part.

I have described what I have done so that you can get an idea, should you wish to try. This was gleaned from information from Leo and reading a lot.

I have also (though it sounds like it’s too late to be of help) just created a post about stripping the core module, since I also found the iFixit teardown rather lacking. Stripping down the Core Module

When you say the FP2 doesn’t work, what DOES happen when you try?