SAFELY finding SOFT short circuits. Macbook A2485 "No Charge" ( not a cap )
606Macbook PRO A2485 has arrived with no/intermittent charge and no boot. USB-C/Magsafe3 only shows 5V and a max of 20mA. Logic board repair is required because data cannot be recovered otherwise.
Need a repair - https://pldaniels.com/repairs
FlexBV5 Software - https://pldaniels.com/flexbv5
In this video we encounter a frustrating soft short circuit of almost 20 ohms. These faults are difficult to track down because in order to have them show up on the infrared camera or alcohol/rosin testing you need to put in too many volts to get sufficient current to flow in order to generate heat;
ie, if you want 500mW of heat out of the 20R short; using Ohms law and Power law;
V = sqrt( P x R )
V = sqrt( 0.5 x 20 )
V = sqrt ( 10 )
V = 3.16V
3v16 is a little too high to risk injecting in to a board unless you already have found where the short is and confirmed it's not something like a NAND, GPU, CPU or other lower-voltage rail that's taking that voltage.
Starting out with 1V, we get...
P = V^2/R
P = 1x1 / 20
P = 50mW :( Not a lot of power
Yes, you CAN just risk it and push 3V in but you might get unlucky.
People wanting to get things done fast and repair/data not the primary concern can ignore all this and proceed to keep with their own preferred method.