If a board gets warm
If a shield or a Nano feels warm, take the power away before you do anything else, and take the Nano out only after that. Most warm boards were plugged in or pulled out with the power on, seated the wrong way round, or have a wire shorting two pins.
Power off, cable out, then lift
If a board feels warm, do these three things in this order, and stop at the first one if you are not sure of the next:
- Take the power away. Unplug the USB-C cable, and anything else that feeds the boards, such as a lead on VIN.
- Wait. Do nothing else while it is still plugged in.
- Only then lift the Nano out of the shield, evenly, a little at each end.
The order is the whole reason for this page. Pulling the Nano out with the power on is how a board ends up half seated, and a half seated board is the case the seating page exists to prevent.
Compare the seat with the rule
The Nano goes into the shield one way round. Set against the rule and the wrong seats on the which-way-round page: USB-C at the boxed USB mark, the arrow reading USB IS ORIENTED THIS WAY, and both rows fully home. Turned through 180 degrees, power pins meet signal holes and signal pins meet the rails. One hole along or back, a power pin meets ground. Neither shows on the surface; a warm shield, or none of the lamps, is how it shows up.
Half seated, bent, or missed
A Nano that is not fully down has one end clear of its holes first. The pins at that end meet nothing, or a neighbour, for a moment. A chip whose supply pin has lost contact while its inputs are still driven can end up powered through its input clamp diodes, which the SN74HC04 datasheet limits to 20 mA. That is a "can", not a "will", and it is one more reason to unplug before you pull.
Look along both rows for a pin that is bent or missed its hole. A bent pin touching its neighbour is a short between two signals, or between a rail and one.
Wires you put there
A jumper wire from a rail to a signal pin is a short between that rail and whatever the pin is driving. A male jumper pushed into the sockets can touch its neighbour. These are the faults you make yourself, and they are the easiest to find: with the power off, follow every wire from its end.
What is normal
The AMS1117 on the Nano can get warm when VIN feeds the board, because it turns the difference between VIN and 5 V into heat and more load means more of it. That is how that kind of regulator works. We do not have a temperature for it, so a warm one is a reason to check the load, not to read a number.
The 22 lamps together draw about 13 mA, illustrative with a 2 V LED. That is not enough to warm anything you can feel.
Before you conclude a board is dead
Take the shield out of it. A Nano on its own, with only the USB-C cable plugged in, should light its ON lamp. If it does, and a port appears, the Nano is alive, and what is wrong is the seat, the shield or your wiring. If it does not, try a different cable and a different port, and a lead you know carries data, before you decide anything.
Where this book ends
That is the first hour: the rule, the two boards, the lamps, the IDE and a sketch that moves them. The reference page has the specifications, what is in the box, and the 3D models and drawings for designing a case.
When it does not work
Unplug the USB-C cable and anything else feeding the boards, wait, and only then pull the Nano out. Then compare how it was seated with the rule and the wrong seats on the which-way-round page. A Nano turned through 180 degrees puts power pins on signal holes.
On USB-C alone, a warm Nano with nothing on its pins is worth unplugging and looking at: a bent pin touching its neighbour, or a jumper wire in the sockets. If VIN is fed, some warmth in the AMS1117 is the regulator doing its job.
Suspect contact first. A board that is rocked or half seated loses its power pins one at a time. Power off, unplug the cable, reseat the Nano with all pins in both rows, and swap the cable and the port before you swap the board.
Before concluding that, unplug everything, take the Nano out of the shield, and plug only the USB-C cable into the Nano. If its ON lamp lights and a port appears, the Nano is alive and the fault is the seat, the shield or your wiring.
Specifications, what is in the box, and the 3D models and drawings for a case.
The reference, and the files →Edit this page — content/books/nano/if-it-gets-warm.mdx
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