Measure the rails at idle and under load, and compare against tolerance

short · 50 min · Objective 5.2

Task

Take real voltage measurements on a running machine at two load levels and compare them against the specification, producing the record that would justify a replacement decision.

Steps

  1. Record the specification tolerances in lab/rails/spec.csv with header rail,nominal,min,max for the three main rails and standby.
  2. Record the wire colour for each rail in lab/rails/colours.csv with header rail,colour.
  3. With the machine idle, back-probe each rail at the main connector with the black probe on a ground at the same connector, and record readings in lab/rails/idle.csv with header rail,volts,within_tolerance.
  4. Apply a sustained processor and graphics load and repeat, recording in lab/rails/load.csv with the same header.
  5. Write lab/rails/verdict.md stating each rail's idle and loaded values, the sag on each, whether any left tolerance, and what your recommendation would be with the reading quoted.

Verify

awk -F, 'NR>1 && NF>=4 {n++} END {print n" rail specification(s)"}' lab/rails/spec.csv
awk -F, 'NR>1 && NF>=2 {n++} END {print n" colour mapping(s)"}' lab/rails/colours.csv
awk -F, 'NR>1 && NF>=3 {n++} END {print n" idle reading(s)"}' lab/rails/idle.csv
awk -F, 'NR>1 && NF>=3 {n++} END {print n" loaded reading(s)"}' lab/rails/load.csv
awk -F, 'NR>1 && tolower($3)=="no" {n++} END {print n+0" reading(s) out of tolerance under load"}' lab/rails/load.csv
grep -Eic '12|volt|v' lab/rails/verdict.md

Four rail specifications, colour mappings, three or more readings at each load level, and a verdict quoting a value. A verdict with no number in it is a suspicion, and the whole point of this lab is the difference.

Notes

If back-probing a live connector is beyond what you are comfortable doing, use a power supply tester and record in the verdict that the readings are at token load only -- which is an honest limitation and exactly the one the lesson names.

This is an independent study companion for CompTIA A+ Core 1 220-1201 and is not produced by or endorsed by CompTIA.