The "donor" flash drive arrived to me today, but although from the same "lot" it uses a different PCB and controller. So, unusable for this repair.
The original resistor has correct voltage.I observed that the original desoldered 1.5 Ω resistor still has some thin metal that flush its top black coated surface.
This extremely small and thing pad, allowed me to mesure the resistor with my multimeter.
Measured resitance was exactly 1.5 Ω.
So, apart from its missing metal pad on one side, this resistor is perfectly healthy.
I tried soldered back this original healthy resistor and tried restoring a connection from the thin metal coating on the resistor surface, but
despite good flux, the solder does not take at this location.
Yes, the donor resistor was defective.The useful maths as suggested by fzabkar also convinced me that there was some problem with the donor resistor (which was taken from a defective USB flash drive). Unsoldered it and measured a resistance around 140 Ω (~ 100 times the one required).
Seeking another 1.5 Ω resistor.I searched among boards that I have if I could find a 1.5 Ω resistor, but this resitance value seems not being broadly used.
1Ω (1R1) and 2.2Ω (2R2) are much more common. Maybe could I try with a 2.2Ω resistor and add a 0.75Ω resistor in parallell if the circuit is underpowered.
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Before doing anything else I'd pull the nand and dump it before you send it up in smoke trying to fix the pcb.
This flash drive simply had a ripped off connector and was not in use when the accident occured.
Under the microsocope is no other damage to the board.
So far, the problem clearly comes from an underpowered controller, due to excessive resistance at the 5V power making not enough current flow.
I don't see risk the PCB going in smoke in such a situation ...
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You might also want to spend some time working on your soldering and get some sensible sized enamel magnet wire for repairs.
I practice weldering for years, and have done many prettier solders, including tiny ones like repairing USB-C tracks.
Sometimes however, you are in a rush and the only thing that matters is restoring the electrical connectivity. In this context,
aestetic doesn't really matter. The solders were carefully examined under the macroscope and are all ok. Also, the wires are not touching other components than they should. All the extra wires visible on the picture were to ensure proper connections in case the PCB tracks would have had a crack.
About suppliesThank you for mentioning the enamel magnet for repairs. This is the kind of supplies I've been dreaming of for long time.
For thin wires, I initially started the hard way, using strands from telephone wire. The PVC coating was the major problem as lacking flexibility.
Then, I found some silicon coated wires. The red one visible on the picture is a 30 AVG, from which I kept here only 3 out of 11 strands.
This cable is very flexible, but the thickness of the silicon coating is the most painful thing for tiny repairs.
Reworking existing cables has always been ok, but for sure, the cables that you mentioned for repairs will be very helpful and bring a much-appreciated comfort.