Simple Metal Pro ceased to function

[NickVDallas]

I have a Simple Metal Pro that has ceased to function. It powers on, but that's it. There may be some red herrings in here, but here's the evolution of the issue:

1. The last few prints using Octoprint failed mindway through as the USB connection failed (as reported by Octoprint). (This is not a USB issue, but this was the first symptom I noticed.)
2. Eventually Octoprint running on Windows 10 ceased to recognize the printer as a USB device. (Windows 10 stopped recognizing the USB connection.)
3. The wires to the part cooling fan fatigued off at the fan. The printer ran fine without it for a while without it - I didn't know there was an issue until I saw the wires dangling below the printhead.
4. At this point, when the printer is powered on the screen comes on and I am able to interact with it.
5. I cannot print the simple square test print that came with the printer.
6. I cannot load/unload filament - the hot end never heats up.
7. I opened the printer to look for any obvious wire issues and see none. (No voltmeter testing at this point.)
8. When powered on, there are two blue LEDs on the power board, one by each ribbon connector (one to control board, one to display)

This printer has a heated bed upgrade (with the then latest control board with the then most up to date firmware sent to me by Printrbot) and I've had to replace the thermistor wires to that bed prior to this as they fatigued out. Other than minor maintenance, this printer has been a workhorse and has hundreds, if not thousands, of hours of print time.

Does anybody have any idea where I should start looking for what the issue could be? I was an engineer so I know my way around electronics, but I'm betting that I'm not the first person that this has happened to and I'm hoping somebody can save me hours and hours of troubleshooting.

Thanks for any suggestions,

Nick

[musk]

In General all errors on the Pro firmware will cause the machine to stop. For example if you send a "print speed scale" modifier command to the printer, the firmware will throw an "unrecognized command" error and just quit working until it's been power cycled. Usually it won't reconnect via USB during this time, which matches the octopi's inability to connect. This firmware on the G2core is only emulating marlin, and all commands are not actually supported. A similar thing could probably happen with broken wires.

I suggest bypassing the lcd screen by jumping the wires shown in this photo: viewtopic.php?f=15&t=11844
That will prevent the LCD from sending any commands to the G2. Then try to connect via USB and attempt to connect with your host software. Watch the command log and make sure you're getting the raw output with all filters turned off. There, you might see an useful error message to lead you.

[NickVDallas]

Thanks for the suggestion! I'll make a jumper and give it a go.