You don't mention it specifically, so just to be certain, did you disconnect the battery first?
I would look at all of the associated filters (on page 21 of the schematic). There are also some MESA filters on page 22.
When looking for shorts, the "normal" way to probe is to set your meter to resistance mode or continuity mode. Then set your black probe to a ground or reference point and the red probe on what you are measuring (you can reverse the probes but by convention, black is ground/reference). What this does is tell you the resistance between the two probes.
When troubleshooting digital circuits, Continuity Mode is used primarily for detecting short circuits. So when we test voltage rails, we don't want "continuity" to ground, we want to see high resistance or OL conditions. Some voltage rails, like CPU/GPU rails are low resistance so they may make some meters beep so you have to look at the measured value to properly interpret the information you are receiving.
Your descriptions below are correct except that you never tried to measure the actual resistance of the rail, relative to ground. You tried the following:
- (1) continuity mode...it beeps from ground (Shield) to Cap ground --> This is normal (they're all connected together)
- (2) Diode mode, with red on ground (shield) and black on ground of cap, I get 0.000v --> normal (see above)
- (3) Diode mode with black on ground (shield) and red on ground (Cap), I get 0.000v -- > normal (see above)
- (4) Diode mode when I put red on ground and black on (Rail) + side of cap, I get 0.577v -->normal if you are probing a component that has a digital IC in parallel
- (5) Diode mode when I put black on ground (Shield) and red on (rail) + of cap, I get 0L --> normal if you are probing a component that has a digital IC in parallel
The results of Number 4 & 5 above suggest to me that the rail is good and not shorted (you are not seeing 0.00V) but it may still be partially shorted, we still don't know for certain. The only mode you haven't mentioned, and it's the one I am asking for, is as follows:
- continuity mode...black probe on ground (Shield) and Red probe on the Rail side of cap --> This is the one you want to use to see if there is a short on the rail and know what the actual resistance is.
Louis Rossmann wrote a great guide here (https://www.rossmanngroup.com/importance...) on how to use Diode Mode for troubleshooting. Lots of repair techs use this but they don't all truly understand the measurements they are seeing. It's not a silver bullet but another tool in your toolbox and the data it provides must be interpreted to be useful. Louis and other successful techs use this technique because they have seen dozens/hundreds/thousands of boards and noticed the small variations and their correlation with issues and resolutions. By themselves, the numbers don't mean much. Most people would be hard pressed to even explain what the meter is doing to the circuit when it is testing in diode mode.
A useful analogy to Diode mode (see #4 above) for testing is like trying to understand the traffic conditions on Broadway by only looking at the traffic going in and out of Manhattan via the Lincoln Tunnel. If you had dozens of "Manhattans", you could probably infer something but on it's own it's not conclusive.
When starting out, learn to do the simple stuff "well" and then add more advanced tools and techniques as you go along.