Bad Day...

Tried to hook up an MPG, think I managed to get 24V on the 5v side 

For context, it is my shiny new Mesa 7i76e, MPG internally shorted, killed the on board 5v, tried to power up with external 5v and blew that diode....
Anyone know the specs of the transistor and the little surface mount fuse?
Should I chuck it in the bin?

The 5V protection Zener is a 3SMAJ5919B-TP
The 5V connector PTC is a MF-NSMF200-2

If the Zener shorted out and protected the rest of the 5V circuitry,
simply removing the Zener may get you back running.

Interesting - so despite the smoke the PTC is still closed

I removed the Zener and fired up with 5v and I can communicate. Giving 24v to field power then allows me to start linux CNC but I get a remote error (29) reported of under voltage - will this be a stored or current error?

Further testing shows that i have:
Working:
Stepper Drivers
Spindle Encoder
Non Working:
Any Field Voltage IO
Spindle Control

I think the non working stuff is the low voltage bein reported - I can see instead of 5v there it is flicking between .2 and 0v

I was looking at the opto isolated Circuit with the weird low readings so ignore that
The A4447 regulator powering the pic chip and optos outputs 3.3v so that looks good.
The A4447 regulator that I assume is used for the 5V power supply (U1) has 5 volts at the output (from the external power supply), this seems to push 4.4v to the input...i assume it is either meant to do that or the chip is blown?

What happens if i try and power up without the Zener at CR17? I cant find any other signs of damage so not sure what is going on Can i just replace that with any 5.6v zener?

appreciate the pointers

OK, good news!

I went and grabbed a standard 5.6v 1w axial zener from the electronics store - pretty ugly and not a 3W (hoping that means it will be more likely to blow in the future....)

Anyway - I can power up from 24v now, 5v power is OK, no more low voltage warning.
All inputs are working again
Spindle control is working again.

Thanks for the assist Peter - this seems to be a testament to how well these boards are designed.

Don't worry Cam,

These things happen.

I managed to kill 2 Mesa 7i96 boards (one through 24v short when I cut the wrong probe wire, one from the plasma EMI into the outputs).

And don't get me started on the amount of Arduino boards I have killed through a wrong wire or stray connection as I'm wiring them at midnight after working all day.