Some time ago I had a FRDM-KL26Z and wanted to measure the processor's current consumption. Therefore I removed R2 and R3 (shunts) and added a jumper J5. Then I loaded code and measured the current in the J5 path. I then wanted to repeated and found that the OpenSDA no longer worked - USB not detected and the LED next to the chip was off.
Since the board was no longer usable I ordered a new one and when it arrived I could program it.
Some time later I wanted to measure the current again so did the same modification on the new board and things were OK - I could do the tests. A little later I applied power to the board via OpenSDA connector (without the J5 jumer in place) and the board died again....OpenSDA not recognised (its D+ line stays at '0') and the light next to it stays off.
So now I have killed two boards just be powering without the processor voltage being switched to the KL26 chip. The KL26 still runs (the program that was loaded previously is operating) but the OpenSDA chip is sort of dead (it has supply voltage, its VREG output is at 3.6V and its reset line is at '1').
I have around 30 FRDM boards in the lab, most modified to measure current and never otherwise had issues. But the FRDM-KL26Z has almost immediately died each time this is done. Why should removing the KL26 power cause the debugger to (seemingly consistently) die?