[GUIDE] Fysetc S6 v1.2 + Octoprint – Fixing USB power problem


I’m used to leave my Pi permanently powered and connected to the board and then I (smart) switch on the power supply only when I’ve to print something.
Since I received this board, I immediatly noticed that was not present a simple jumper in order to select which 5V should be used for the logic: if the one coming from the onboard DCDC or if the one coming from the USB.

If you’re using OctoPrint (or any other host) with this board you have probably faced out this problem: when you have your board connected to a USB port and you turn on the printer power supply, the screen starts to dim and became almost unreadable.

Searching on the web for this kind of issue was not so usefull. I tried also to contact the support without success, they said that is not a problem related to the board design but strangely in the v2.0 they modified this section.
The only usefull article comes from the OctoPrint forum, here, where there is a complete explaination on why and why not to power the board from usb, as well as a workaround that consist in putting a piece of electrical tape on the power pin on the USB connector.
Unfortunately this not worked for me and when I tried it I was not able to get my printer detected from octoprint.

The problem

When you turn on the printer power supply and you have the usb connector already plugged in a RPi you may notice some problems:

  • Screen dimming or blank screen
  • TMC connection error
  • BLTouch error
  • Board restart

All of this problems can be exploited by placing an oscilloscope on the 5V rail (labeled +5V on the schematics) and are due to a design mistake on the Fysetc S6 v1.2 (fixed in v2.0).

As reported here and here, the voltage will drop to around 4.4V and cause this problems.
In particular, it comes from the 5V rail selection circuit (picture below, taken from fysetc repo) that is meant to chose the “best” 5V supply depending on what is present.

Fysetc S6 v1.2 5V Supply
Fysetc S6 v1.2 5V Supply

Usually there are specific ICs that are suited for this kind of operation (you can search for it).

I’ll analyze in detail the circuit and explain why it is not working in a dedicated post.

The solution

Since there is no way to manually select the 5V that we want to use to power on the logic side, we have to go with the heavy part: desoldering some components.

In particular, I’ve rebuilt a schematic by looking at the board and finding which is what. You can find it below:

In order to permanently select to use the onboard DCDC to provide the 5V rail you have to made the following adjustments:

  • Remove Q5
  • Remove Q10
  • Make a jumper between pin 2 and 3 of Q10
  • Not mandatory but prevents useless power draw: remove R6 and R46

The result:

As you may notice I’ve removed the diode too, but it’s not mandatory.

Now everything works flawlessly and I’m able to remotely power on and off the printer without any kind of issue.

Hope that it is useful for someone, don’t forget to support me and like my social media pages.

Comment below for any kind of information or support.

2 thoughts on “[GUIDE] Fysetc S6 v1.2 + Octoprint – Fixing USB power problem”

  1. thanks, man. I really appreciated your post! I just got 2x S6 that were meant to be v2 but are actually v1.2. I’ll try your “fix” on one of them, hopefully I’m not gonna destroy everything 😀

    • Glad that you appreciated this! If I’ll need any support in the process feel free to contact me here or in private!


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