[BUG] Failing to boot (BSOD) after installing MMU3 on MK4

[pars3cproton]

Printer type - MK4 + MMU3

Printer firmware version - 6.0 RC1, RC2, Final release

Optional upgrades - MMU3

Describe the bug After installing the MMU3, everytime the printer is turned on it tries to boot, it fails once, tries to boot again and then shows a BSOD message (the same message no matter if it's 6.0 RC1/RC2/Final release.

The only possible fix is "touching the cables" of the MMU3 while it boots, as shown in the video attached (you can also see the message in the video). https://drive.google.com/file/d/10S5PZIgaxnuu6wRmS4JdfCftR7sWLvyO/view?usp=drive_link

With support we thought it was one of the two mmu3 boards fault, I tried replacing them but got the same error. Then I bought another printer to mmu3 cable thinking that was the problem, but it's still showing the same behavior.

Support already has a dump file, but feel free to ask for a new one.

As of now the printer is usable if I boot it touching the cable behind the mmu3.

I tried everything, clearing MMU3 eeprom, factory resetting the printer but nothing seems to work.

[tlachmann]

I hope Prusa also recognize that behavior. For today released 6.0.2. FW the changelog doesn`t show anything.

I also investigate regading the pulsed prodcedure, and after changing to a larger shunt, I could observe some artifacts that lokks like the pulses, before it was hidden by disturbances. But of course the artifacts are so minor, that it doesn`t take account to reduce inrush current.

you can see the artifacts by the pulsed procedure in the small slope of the blue line before it rises vertical

[tschaerni]

I few days ago I received a new xBuddy board and a new MMU3 board (and a new power panic cable, as I have an earlier revision with the 4 screw gearbox cover).

After replacing them, it seems to work without issue so far (crossing fingers).

Maybe the Issue is mitigated with newer versions of the xBuddy board?

Could be helpful to gather information about the revisions of the printers/xBuddy boards?

[GvnCampbell]

I contacted support as well with the same issue. We did a bunch of tests. If I unplugged the cable from the mmu3 it still happened. Once I fully removed the cable from mmu3 and buddy board it would boot up fine. So they think it was the cable and shipped me a new one that comes tomorrow.

I did share them links to this issue though in case. We will see if the new cable works.

[tschaerni]

I contacted support as well with the same issue. We did a bunch of tests. If I unplugged the cable from the mmu3 it still happened. Once I fully removed the cable from mmu3 and buddy board it would boot up fine. So they think it was the cable and shipped me a new one that comes tomorrow.

I did share them links to this issue though in case. We will see if the new cable works.

Hm... I didn't had that issue, it worked fine with the cable connected to the xBuddy board but not the MMU3, it even worked fine with the PD Board connected to the cable, but disconnected from the MMU3 board.

But yeah, maybe you just have a faulty cable, even tho I can't really imagine the cable being the culprit, unless there is a short in the cable somewhere.

[GvnCampbell]

I contacted support as well with the same issue. We did a bunch of tests. If I unplugged the cable from the mmu3 it still happened. Once I fully removed the cable from mmu3 and buddy board it would boot up fine. So they think it was the cable and shipped me a new one that comes tomorrow. I did share them links to this issue though in case. We will see if the new cable works.

Hm... I didn't had that issue, it worked fine with the cable connected to the xBuddy board but not the MMU3, it even worked fine with the PD Board connected to the cable, but disconnected from the MMU3 board.

But yeah, maybe you just have a faulty cable, even tho I can't really imagine the cable being the culprit, unless there is a short in the cable somewhere.

Well I can confirm that its not the cable. I got the new cable. Replaced it and same issue.

I can keep hitting the reset button and it eventually boots up but its still very annoying.

Back to support I go.

[m-cas]

So far, the only success reported has been from people with new boards sent to them from support (I am not including the workarounds like pressing reset, adding a cable to nowhere, and bending the board/cable on the emu while booting). New cables have been sent multiple times already and apparently w/o changing the outcomes. Two things would be really interesting:

• a word from Prusa
• hearing from those that got new boards that work, if they can spot any difference from the previous ones

On Jun 13, 2024, at 14:48, GvnCampbell @.***> wrote:

I contacted support as well with the same issue. We did a bunch of tests. If I unplugged the cable from the mmu3 it still happened. Once I fully removed the cable from mmu3 and buddy board it would boot up fine. So they think it was the cable and shipped me a new one that comes tomorrow. I did share them links to this issue though in case. We will see if the new cable works.

Hm... I didn't had that issue, it worked fine with the cable connected to the xBuddy board but not the MMU3, it even worked fine with the PD Board connected to the cable, but disconnected from the MMU3 board.

But yeah, maybe you just have a faulty cable, even tho I can't really imagine the cable being the culprit, unless there is a short in the cable somewhere.

Well I can confirm that its not the cable. I got the new cable. Replaced it and same issue.

I can keep hitting the reset button and it eventually boots up but its still very annoying.

Back to support I go.

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[HaWiWe]

Still not working. Got new boards for the MMU, no luck. So it must be something with the printer itself. Support is still trying to find the reason.

[Subtle3D]

I've still had it happen occasionally on a few of mine. The cable to the MMU3 workaround is sporadic but removing the usb drive from the screen before turning on the printer has worked every time so far.

[GvnCampbell]

The only way I can get around it at this point is to turn off the machine and the raspberrypi for about 2 minutes. Then the machine boots up fine and then I turn on the pi. Its like I gotta give it time for everything to discharge.

[Subtle3D]

I've still had it happen occasionally on a few of mine. The cable to the MMU3 workaround is sporadic but removing the usb drive from the screen before turning on the printer has worked every time so far.

Well, I spoke too soon. I now have one I can't get past the overcurrent screen. The last 4 with the USB removed must have been a fluke.

[Subtle3D]

I don't know which influence the USB cable from scientific side has. in the schematic of PCB version 0.3 the ID pin of the microUSB cable isn't connected, normaly the ID Pin controls switching from USB Slave to OTG. If it would be connected to MCU and maybe the cable has that pin grounded, then I could imagine. For me the USB cable is more or less a esotherik thing.

But even the fact, that the difference of an 0.002 Ohms Resistor (some cables has higher resistance) fixes the behavior on my side, is also not explainable, at least not at that tiny value.

On the other hand, I´m sure that a resistor between 1 and 1.4 Ohms on the 24 Volts Input of the PD-Board could act as a current limiter. On the other side, this value shuldn´t also not have a influence to the Stepper functionality.

Greets Thorsten

I've now put a 1 Ohm 1 Watt resistor on each of the 2 red 24V wires to the MMU3 and it's worked. We'll see if that holds.

[ntruchsess]

I've now put a 1 Ohm 1 Watt resistor on each of the 2 red 24V wires to the MMU3 and it's worked. We'll see if that holds.

I had the same issue (false overcurrent error) with my MK4 + MMU3 and adding 0,5 Ohm Resistance to the 24V Supply (2 times 1Ohm added to each red power cable) solved it instantly. Prusa should modify the power-delivery board that sits in between the cable and the mmu-controller-board and add such current-limiting resistor with the next hardware iteration.

[flippedcracker]

Can you add a picture of how you added the resistors?

[Subtle3D]

Can you add a picture of how you added the resistors?

No problem.

For an update, I've now soldered in these 2 1 Ohm 1 Watt resistors on all 8 MMU3's and haven't had the issue on any of them since.

The sleeve will fit a little better if you offset them like in the picture.