I have a Smoothieboard 5X v1.0b, couple years old but hasn't been powered on until now. USB powers up the CPU & LEDs blink properly and I can flash firmware no problem. Latest firmware installed as of a couple days ago.

Disconnect USB, then apply 24V to the VBB input on the big jack and nothing. No lights, no nothing. Double checked the polarity, initially got it backward but for only a second or two before shutting down and re-checking the wiring diagram. I do have the RECOM 5V regulator installed, and tried two different units, with the same issue.

What component would likely blow up on a reverse 24V situation?

Thanks in advance…