Finding Shorts Fast
Power & Chip-Level Faults
Preview
A short is a direction, not a location
When a rail reads near zero ohms, something downstream is pulling it down. You do not swap parts randomly - you divide the board and follow the resistance to the fault.
Three fast methods
- Resistance divide - probe the rail at multiple points; the lowest reading points to the fault leg
- Inject & heat - feed a low voltage at current limit; the shorted part warms up (thermal camera is the professional way; a careful finger or isopropyl on small boards also works)
- Diode-drop compare - compare each suspect component's readings against the same part on a working board
Work from the power entry
- Check the fuse and the input rail first - a short near the port kills everything beyond it
- Isolate in half: disconnect or lift components one leg at a time where safe
- Confirm the repair by re-checking the rail reads normal after removal
Warning: Voltage injection at too high a current or voltage can fry surrounding chips. Start low (1V) with a strict current limit and raise slowly.
Practical exercise
- Create a short on a scrap board, then find it with the resistance-divide method
- Repeat using voltage injection and note the hot part
- Record which method was fastest for each point
Check your understanding
What is the first thing to check before chasing a rail short? The fuse and input rail near the power entry.Why start with a low injection voltage? To avoid damage to surrounding ICs while the fault heats up.
This is a free preview lesson
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