Weird transistor behavior: always 24v on (+) and 22v on (-) ?!? [Azteeg X3 pro]

Hello,

Thank you for taking the time to try and help me.

Upon first wiring my 24v hot end to my 24v powered Azteeg X3 Pro, the hotend started heating up immediately on power up.
I confirmed it was not a firmware issue by uploading the "Blink" arduino sketch.

I pulled out my meter and indeed measured 24v on the (+) output for all hot end outputs on the board.
I then measured the voltage between the (-) side of those outputs and the power supply GND and found a voltage of 22v

I pulled the board to do a visual inspection (see attached imaged) fearing maybe a burnt transistor, and found 2 diodes missing (They look like they were there, but I can't find the in the printer) and 1 diode partially disconnected.

One more detail I need to share: the hotend heater had one end wired to the (+) of the heater outputs on the board and the other end was wired directly to ground (not the (-) outout of the transistor on the board).

So...

1) Did I fry my board?
2) Was my wiring scheme to blame?
3) were those diodes supposed to be there?!
4) Can I possibly repair the board?


Any tips to answer the above or how to further troubleshoot are greatly appreciated.

Thanks!

-Leav

Useful links section:
Azteeg X3 Pro page
X3 PRO wiring Diagram
X3 PRO Pin Definitions rev A
Source File - (schematics, Diptrace PCB design software)
X3 PRO 3D assembly file (STEP)

Quote
Leav
One more detail I need to share: the hotend heater had one end wired to the (+) of the heater outputs on the board and the other end was wired directly to ground (not the (-) outout of the transistor on the board).

Most boards usually switch the GND side and not VCC, so the board sounds like its working as expected. Hook up the other wire to the - instead of directly to GND and it should work properly.

"I pulled out my meter and indeed measured 24v on the (+) output for all hot end outputs on the board.
I then measured the voltage between the (-) side of those outputs and the power supply GND and found a voltage of 22v"

this is expected, the GND is switched on most boards, so you must use the GND on the output not direct to the supply.

The diodes seem to be related to the stepper drivers, I suspect an attempt to protect the drivers from damage when you move you axis manually and generate electricity into the chip. As a guess Only X Y and Z are protected, as most people don't try and manually move their E. If your feeling paranoid.. add them. I would fix the damaged one.

Edited 2 time(s). Last edit at 05/02/2017 11:09PM by Dust.

Thanks so much for the input regarding the voltage! that's news to me and a load off my mind! I thought I fried the board!

Regarding the Diodes: Based on their location, I'm 99.9999% sure that they are not related to the steppers based on location (far away from stepper drivers, very much adjacent to each hotend output).

Does anyone have an azteeg they can flip over and check to see the status of the diodes?

re diodes, your right, I had your picture upside down in my head... far to many mosfets than im used to


So its mosfet protection. So yea no protection on the last two mosfets...
You need protection when dealing with inductors, (fans and solenoids, coils etc) the collapsing magnetic field can kill a mosfet

I think its diodes are meant to be there

Sorry I dont have a real one to look at