A minute with a multimeter before the first power-on can save a board. Check the supply for a short, and check polarity.
What the message means
Most burnt boards come from reversed supply or a short between positive and ground. Both are easy to check with the power off.
Fix it in this order
- Disconnect the battery. Set the meter to the continuity or low-resistance range.
- Measure between the supply positive and ground. A beep or near-zero reading means a short.
- Check the battery polarity with the voltage range before connecting the board.
- Look for stray wire strands, solder bridges and bent leads.
- Power on with a current-limited supply or a fuse if you can, and watch for heat in the first seconds.
- Measure the voltage at each board before connecting the next one.
Why it happens
A short circuit is a low-resistance path between positive supply and ground, which lets current rise far beyond what the wiring or regulator can handle. Heat builds quickly at the weakest point. Reversed battery polarity is the other common killer, because it can force current through parts that were never meant to carry it. Both faults are easy to find with the power off, when the meter reads resistance instead of voltage.
Capacitors on the board are discharged while power is off, so a resistance reading across the supply and ground should be high, and it may climb slowly as the meter charges them. A reading that stays near zero, or a beep in continuity mode, points to a short. Checking each new module one at a time limits damage, because the fault is then traced to the last part you added.
If you see this, do this
| You see | Do this |
|---|---|
| Beeps between supply and ground | Short. Find it before power. |
| Part gets hot at once | Disconnect power and check polarity. |
Confirm the fix
- Set the meter to continuity, touch the probes to the supply rail and ground with power off, and confirm there is no beep.
- Check battery polarity on the voltmeter’s DC range before connecting, and confirm red goes to positive and black to negative.
- After connecting, with a current-limited supply set to a low current limit, read the rail voltage and confirm it matches the regulator’s rated output before adding loads.
Common mistake: Many builders assume a board that powers up and lights an LED is free of shorts, but a short can sit on a rail the LED never tests, such as a motor supply or a module’s ground.
Related
common ground, barrel jack polarity.
Last reviewed: November 2026. These are the usual causes and the order that finds them fastest. Test on your own board; clones and cables differ.