Instructions | Jumpstarting a drowned phone

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Step 1

Take apart your phone.
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Step 2

Find capacitors close to the important semiconductors - in this case the processor and the FLASH memory.
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Step 3

Find out which electrode of those capacitors is ground, by finding a ground point elsewhere on the circuit. A ground point is easy to find with a capacitor that has polarity, such as the big yellow capacitor that I attached my ground wire to. Use the beepy thing on your multimeter for this (a more technical term would be continuity tester) - the most valuable yet least valued tool in the assortment of a debugger.
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Step 4

solder some wires to the hot side (voltage supply side) of those capacitors, and one wire to the circuit ground
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Step 5

make sure the phone battery is fully charged (I used an external charger circuit)
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Step 6

attach battery to circuit with tape
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Step 7

attach usb cable between phone and computer
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Step 8

carefully give the circuit some voltage. Phone circuits typically work at 1.8 VDC, but it may even be lower.
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Step 9

(try to) start your phone
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Step 10

If this doesn't work, try slowly to increase the voltage in steps, and try to start the phone again. Be careful though, that it doesn't rise too high.
Also, you could try adding more wires to more capacitors, because perhaps a vital part of the circuit is still unpowered.

Jumpstarting a drowned phone