MP3DP V4 and BL Touch Troubleshooting

I have almost completed my second build of the MP3DP V4 but I have one clear issue. When homing the Z axis, the BL Touch extends the trigger out but once the bed gets there it just blows right through it and crashes into the nozzle with no remorse.

I have tested the BL Touch using the touchscreen and navigating to the probe settings where I can manually extend, retract, and test it. The BL Touch moves as expected, at least I think it does. Everything else on the machine works (X homing, Y homing, nozzle/bed heating, extruding, etc.)

Any ideas of what I should check on?

SKR1.2, Marlin, Klipper or something else? If Klipper, shared my Octopus config here.

I am running Marlin on my machine. It is the same exact setup as my first build and I never experienced this, so it must be something simple I am missing.

Cool, nice that you have a working reference machine… Would swapping BL touch probe between the machines help to narrow down whether issue is with the probe, and/or wiring, and/or firmware and/or saved config?

While that is a good idea, I would have to do a lot of unwiring and taking the wire sheathing off to get the one off my other machine. I may actually just order a new BL Touch to test unless anyone else has other ideas.

I had a problem similar to this. The probe would deploy but not do anything, rewired it correctly and then the probe would not deploy. The sensor inside the BLtouch was cooked. Had to replace the BLtouch. The CRtouch or Biqu microprobe are options as well the the BQ v2 being the least of the 3. I hope that isn’t it, but at least your system board isn’t cooked.

So a new BLTouch showed up yesterday and I gave that one a try. No luck. Same thing happened. Homing Z does it’s normal thing (homes X and Y, goes to middle of bed, deploys BL Touch) and then the Z just keeps on trucking right through the BL Touch sensor, crashing into the nozzle and making beautiful noises.

Here is my wiring. Maybe I have something wrong?

so you are running marlin correct? and you have a similar one already that functions, so this is a system specific issue because your other system is the same and works?

I am running Marlin, correct. From what I can tell comparing the two machines, they are wired the same. Let me take a look again to be sure.

I run klipper, so I know there was some setup to get the BL touch to act as the z end stop, but doing that in Marlin is unfamiliar, but you have already done that with the original system. You have the same firmware/compiled version on both systems?

As far as I know.

I flashed my new printer with this:

I put the FIRMWARE.bin on the microsd, flashed it, it blinked green some, and then the file extension changed to .CUR. And again, everything else on the machine works just fine so I feel confident the firmware is good.

I remember the BLtouch having 2 IO’s. one is for extending/retracting the probe end and the other is for detecting its movement. Is there a way to test just the bltouch from the Marlin firmware like you would check the endstop status? In klipper, i can terminal command the probe extension and then query the touch state. The one bad sensor I fried by connecting it to the wrong pin header (honest mistake) would extend and retract, but never detect. It seems unlikely that you would get two of these that the sensors are both bad, but I know there was some discussion of BLtouch wiring differences based on version that the wiring pins were different. You might need to verify power and ground and sense wiring. on the BLtouch.

On the BLTouch, the wires are (left to right)
Ground, +5V, Servo, Ground, Signal.

That lines up with how you have the servo wires, so makes sense.

The blue and black wires are weird though. Blue is ground, and black is signal. It looks lime you have the black wire going to ground at the end stol, and vlue going to the signal wire, but with the wire order from the BLTouch docs, thisnjs reversed.

I would actually expect this to have the Z stop as always triggered, but maybe not. It certainly wouldn’t work.

Try reversing the blue and black in the end stop plug and see how that goes.


Ahhh, let me try that later on and see if that fixes the issue.

BINGO. Flipped these around and now we are rolling. Thanks!

I had always thought that +/- order of the endstops didn’t matter. Perhaps that is only with typical contact switch endstops…

Yes, with the typical switches that is true, but the BLTouch is using active circuitry. Semiconductor circuits often only pass one way, whereas the switch doesn’t care.

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