I'm trying to find a short to ground on a Nintendo Switch of which there are no schematics.
The short is present on the 3v3 line.
What I would like to do is inject power into this line from my bench top power supply to see if the short presents its self with heat.
What I'm asking is the point of injection into this line important or can it be anywhere on the line as long as it is the 3v3 rail obviously.
You can vary the point of injection to help you locate the position of the short.
Use two probes. One probe injects current. The other measures voltage with respect to ground. Use two so the voltage measurement is not corrupted by the variable drop you will get between the current injection probe and the track.
You can use either (or both) of these strategies. The first is to inject current at some random point, then move your voltage measurement probe around the 3.3v net. Lower voltages mean you're getting closer to the short. The alternative is to probe the voltage at some random point, and change the points at which you inject current. Again, lower voltage measurements mean you're injecting closer to the short.
As a repairman who fixes logic boards almost every day (including shorts, of course), here's the advice:
First of all, it doesn't matter at all where exactly you inject the voltage on the same line, as long as you're sure it's the correct line, you're good (a proof of which is a fixed 0.00V on the line). Can be a resistor, a cap, an SMD chip, whatever, all the same, they're all connected to each other. There is very little chance that you will inject the voltage exactly into the component which is shorted, but I only heard stories of that, never happened to me in several years of experience.
Second of all, start with injecting something like 1V with 1A limit, if it immediately draws max current and pulls power supply voltage down, you may want to increase current limit to 1.5A or 2A. If the current is not hitting the ceiling, you can turn the voltage up to 2V. After that while the power is still applied and the short is wasting precious milliamps, you can start touching the board everywhere in an attempt to find the warm spot (as you probably know if you know that you should inject voltage). If nothing shows up, add a little more voltage and current. You don't want to send 3A right away, you may damage traces which are not designed to carry high current. They can take an amp or two for 10-15 seconds with no harm, so basically apply power, touch-touch-touch-touch, shut down, wait 5 sec, apply for 10-15 sec again. The more current it pulls, the shorter time you apply power. If it's some 3Amps, it's better to apply it for 5 seconds max with 5 seconds pause. Apply - touch-touch-touch in some area, turn off. If still nothing shows up, you can actually touch it with lips, sometimes some thick beefy caps don't get very hot and you can't find them immediately, it's fine (but usually you can immediately tell and it's really hot). You'll find warmer place. Sometimes you can also kinda think that something is warm, but it's your brain tricking you, and you have only probably warmed some capacitor up by holding fingers on it.
