Ender 3 Max USB Connector

What is the problem?

Not a problem as such, more of a question. I have an Ender 3 max with a 4.2.7 main board and would like to know if the printer needs the power & ground wires connected for the USB to work. If not I'll splice a micro USB into a 5 amp USB-C cable to charge the phone & print simultaneously. Then the printer won't complain when the power is off & the USB is still connected. My printer disconnects randomly but reliably when using Octoprint on a Pi4, I came across Octo4a yesterday & installed it on an old phone this morning. I had a print going which started normally but after about 3 hours the camera stopped. I didn't worry about it, the printer was still going strong. A couple of hours later the print stopped, I was ready to jump on the printer but instead I came on this forum & saw that someone had good results wrapping the board in tin foil. While doing that I had to move the phone & that's when I found the battery was dead flat, the phone had died & killed Octoprint.

What did you already try to solve it?

I have ferrite beads on all the cables, stepper motor cables too.
I have wrapped the motherboard in tin foil but not tested yet

Have you tried running in safe mode?


Did running in safe mode solve the problem?


Systeminfo Bundle

You can download this in OctoPrint's System Information dialog ... no bundle, no support!)

I didn't do this because I hope someone can say yes or no to the question

Additional information about your setup

What kind of hardware precisely, OctoPrint version, OctoPi version, printer, firmware, browser, operating system, ... as much data as possible


It should work fine without the 5V wire. I got the same board and taped the 5V off :slight_smile:

Be careful when you wrap the board in tinfoil. Leave room for fresh air (there are active components on in that need cooling) and don't short anything out.
The culprit for the connection dropouts is often the display / display cable. If you got the phone next to the printer anyway you could try to disconnect the display cable from the mainboard and use your phone as display.

Thanks for the reply..
I hadn't thought about the display causing the problem so I'll try running the printer without it.
The mainboard had been sitting next to the printer in a plastic tray I printed, I did that when I first started having the problem to get easy access, it's now in a cardboard box with holes at each end & wrapped in foil. The printer is inside an enclosure tent while the power supply & the display are outside of it.
I'll make up the cable, disconnect the display, try a print & let you know how it went

I removed the display & ribbon cable, motherboard wrapped in tin foil, used the Pi4 instead of the phone, clean install of Octoprint/Octopi, did a 7.5hr print followed by a 2.5hr print with no issues.
I'll mark this as solved but I'll know for sure in a couple of weeks.
Thanks :+1:


also, you do need the ground, just not the +5v

I thought about that after I asked the question, the data cables will need a complete circuit.
All good & fingers crossed, all is well here.
Thanks for the reply