Troubleshooting Tools — 220-1201 Study Guide

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Included in this chapter:

Aspect	Multimeter	Power-supply tester	POST card	Cable tester
Fault family	Power	Power	Boot	Signal path
What it reads	Exact voltage, continuity, or resistance at one point	All rails plus Power-Good at once	Two-digit hex code where POST halts	Wiremap: opens, shorts, reversed and split pairs
Power state	Voltage live, continuity and resistance dead	PSU unplugged from the board	Card in a slot, machine powering on	Cable disconnected at both ends
Reach for it when	You need a precise value or to check a fuse	You want a quick go/no-go on the PSU	There is no video to read a boot error	A run has no link and you suspect wiring

Cheat sheet

Measure voltage with the power on, continuity and resistance with it off
A multimeter reads voltage, resistance, continuity, and current
ATX rails are +3.3, +5, and +12 V, good within about 5 percent
Use continuity mode to tell a good fuse from a blown one
The power-supply tester gives a quick go/no-go; the multimeter gives the exact value
A PSU that passes an unloaded tester can still fail under real load
No Power-Good signal means the board never leaves reset
A POST card shows the code where boot halts when there is no video
POST progress codes are written to I/O port 80h
Onboard CPU, DRAM, VGA, and BOOT LEDs replace a POST card
Distance to a cable fault needs a TDR, not a basic cable tester
When a run has no link, test the cable first, then the port
An ESD spark too small to feel can still kill a chip
Never wear an ESD strap near a CRT or an open power supply
Power down and unplug before you work inside a machine
Keep a work area near 40 to 60 percent humidity to limit ESD
Read a wall outlet on AC volts, but a battery, adapter, or PSU rail on DC volts

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