Hey all, just finished debugging an interesting problem.
I was trying to program a chip in a custom test fixture I created for the purpose. My programmer would not recognize the chip.
I was checking for shorts with my multimeter on the 200 ohm setting. After some time I realized the resistance might be much higher if it was a small short. I set my meter to the 2 megaohm setting. With the chip in the board, I found that VCC and GND were shorted.
I removed the chip just to be sure it was the board, but then I noticed that the board was fine. Everything checked out.
I looked over at the chip, and realized the problem. I checked the chip out of the fixture, and measured 55.5k-ohm across pin 30 (AVCC) and pin 31 (GND).
I quickly tested my fixture with a spare ATM324P that I had (in case something like this happened), and the pins were not shorted, and the fixture worked fine.
Now the absolutely perplexing part is that the "bad" chip CAN be programmed, but only on a breadboard. The only difference between my fixture and the breadboard is that the breadboard has 0.1uF decoupling caps across VCC and GND, and a 47uF electro across the main supply. I don't see how capacitors would mitigate the effect of a short circuit.
The current between pin 30 and 31 would only be (5V / 55.5kOhm = 90uA), which is almost negligable.
I'm also wondering what might have caused this kind of a short to occur. What's really strange is that although the bad chip can't be programmed in a properly wired test fixture, it will still run its program properly.
My mind is blown. I have no idea what's going on.