Pat,
Doing component level repair is really all about the tools, and a background in electronics. Mine is from the military and as a civilian, but it doesn't take but a few weeks with YouTube, or volunteer courses
like this one, and you are all set!
"Heck, just reading your post is like me trying to read a different language i have never come across, but i do get a gist for what you are attempting to do."
Let me see if I can decode it enough to capture your interest:
-The purpose of the above
R5750 is actually quite simple: It is there to allow a device to the right to measure a voltage.
-On the left, you will see that the aptly named
PP3V3_SSD_ISNS_R signal supplies a voltage, and
PP3V3_SSD_LIM is the return. Just look at the arrows."
LIM", as you can imagine, is for "current
LIMiting".
-"
ISNS_R" stands for
I (symbol for 'current')
Se
NSe Resistor. Note the 2 signals on pins 3 & 4 with the suffixes
_P (
Positive) and
_N (
Negative).
-"
Ohm's Law" shows that when current flows through a resistor, a voltage 'drop' forms across the resistor.
-This means that you can measure how much current is flowing through a resistor by measuring the voltage dropped across it. Since
I = E/R (formula meaning "
Current = Voltage dropped (i.e. divided by) over the known Resistance"), we can measure to see if there is too much current going through this circuit, I would assume for the SSD.
-So for an example, if we know the resistor's value is
10 Ohm (
ohm = measurement value of resistance), and we measure
2 Volts (
the 'E' value, volts are measured in Volts), Current ("I") is simply
E/R, or
2V/10 Ohms or
0.2 Amperes (
"I" for current is measured in Amps).
-0.2 Amps is also called "
200 millAmps", or simply "
200mA".
-If, for example, that measuring device off to the right (
the INA210s & INA214s I mentioned in OP) shuts down the power rail
PP3V3_SSD when current draw is over, say,
150mA, then the above condition shows a [
partial] short to ground, and to protect more expensive electronics, it will turn that power bus off, or something.
Here is how the symbols on the schematic above break down:
OMIT - Can mean either do not put on the board at all, or only to not put it on automatically with machines that place these tiny parts (robot arms). I don't know which in this case.
0306-SHORT - This means the size of the device is EIA number
0306, which you can look up at a place like (I have no permissions to put in this comment):
Mechanical Dimensions for Capacitor Chip Devices, SM Package Sizes So, 0306 is 0.063" x 0.032" x 0.013" (nobody memorizes, so a chart is handy!)... The "
SHORT" means that at just
0.005 Ohms, it is
essentially (but not quite) a short (i.e., no resistance at all!).
Q: "Why such a low resistance?"
A: Because it the resistor was much more resistive, it would start taking signal away from the (in this case) SSD subsystem. We want our measurement parts to be as unobtrusive as possible. 
MF - Metal Film (the type of material the actual resistor is made of)
1/3W - this resistor can only take 1/3 of a
Watt ("W") before it will blow.
note:
Watts can be calculated several ways, with one of them being I x E, or Current x Voltage. Too much of either, and it will blow and in overheating present an 'open' circuit (no connection at all between pins 1 & 2).
1% - Tolerance - The value of resistance is guaranteed by the manufacturer to fall between + or - 1% of the stated value. This isn't followed closely by off-brand suppliers...
0.005 - This is the actual resistance in Ohms. You will see things like
5k for 5,000 ohms,
2M for 2,000,000 Ohms, and other metric 'multipliers'.
R5750 - This is Apple's designation. Good for finding on a drawing or schematic, like a cross-reference, but nothing to do with the part itself, except
R is for
Resistor,
C is for
Capacitor,
D is for
Diode,
Q is for
transistor,
U is for
microcontrollers or simple ICs, etc.
Once you know how to decode these components, they aren't so intimidating.
-pat
I'm sorry, I sure can't help, but i certainly respect what people like you can do.
Heck, just reading your post is like me trying to read a different language i have never come across, but i do get a gist for what you are attempting to do.
======
