I am still in the process of flashing my very first micro controller (an ATmega32U4). In the whole process of learning and exploring how to get this done I also used a multi meter several times on the ATmega to see if a certain pin was high (to check if my program was active, in other words, if I finally successfully written the flash memory).

Since I am still a bit clumsy with electronics, I put the probe on two pins at the same time; ground and VCC.

I noticed that suddenly stuff reset, and my power supply started to make a different sound. I didn't even realise straight away what I did, but after a while I finally realised, "oh $@!#, I am creating a short with my probe...".

Now aside from the fact that that was a rather stupid thing to do, is there any way I can test of the ATmega chip itself is still OK?

  • \$\begingroup\$ Verify Vdd with dc and ac ripple then fix or replace if bad and try again. tape needle/pin to probe pins for smaller footprint. using really strong thin tape. e.g. Tuck Tape for sheetrock. \$\endgroup\$ Apr 16, 2017 at 18:35
  • \$\begingroup\$ @TonyStewart.EEsince'75 any chance you can dumb things down a bit? Verify Vdd with dc and ac ripple then fix or replace if bad and try again \$\endgroup\$
    – bas
    Apr 16, 2017 at 18:39
  • \$\begingroup\$ verify supply is Ok, measure voltage on pins , not just port resistance. \$\endgroup\$ Apr 16, 2017 at 18:39

2 Answers 2


There are many ways to find out if an MCU is faulty or not. Here are some:

  1. Obviously, if you hava a programmer try to program the MCU. If it failed that means a defective MCU.
  2. Setup the essential MCU circuit and power the MCU up, there should be no noticeable raising up in temperature.
  3. In case of new ATMEGA and it is not programmed yet, with a voltage meter, the measured voltage should be the same on all the IOs.
  • \$\begingroup\$ Actually, failure to program does not necessarily mean a defective MCU - many chips and especially the ATmega series can get into a state where normal programming is not available but more, "extreme" programming (using a higher voltage mode, etc) is workable. Other devices can depending on last state require careful reset synchronization with the programmer connection, etc. \$\endgroup\$ Apr 17, 2017 at 1:38
  • \$\begingroup\$ @Chris Stratton Yes you are right, but here in this context (talking about a short circuit and if the MCU has been demaged or not), not being able to reprogram the MCU anymore is a good indicator if the MCU is damaged or not. I am not making any further assumptions like 'if he has changed the fuses of the MCU or not'. \$\endgroup\$
    – Macit
    Apr 17, 2017 at 8:49
  • \$\begingroup\$ I don't know if an ATmega is susceptible to it, but there are parts where various abnormal conditions can end up changing programming settings like fuses, runaway bad programs can inadvertently lock out debug interfaces, etc. \$\endgroup\$ Apr 17, 2017 at 21:29

Chances are the power supply just went into current limit mode (hence the sound) and you're okay.

Permanent damage tends to come from putting more than Vdd or less than Vss on a pin, or from overvoltage on Vdd. Or it comes from triggering latchup, in which case the chip would have gotten very hot.

It's not going to be possible for you to exhaustively test the chip with the equipment and information you have but if you can wiggle each of the I/O pins or read them programmatically and the chip is not drawing excessive current it's probably fine. If you think the probe pins might have slipped onto a GPIO pin as well, test those.

  • 2
    \$\begingroup\$ Both your answers make a lot of sense. I accepted Majids answer, he needs the points harder then you do :) (but thanks a lot all the same! helpful stuff for a newby like me!) \$\endgroup\$
    – bas
    Apr 16, 2017 at 19:03

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