Kit built Ender three fails on Z axis calibration and auto bed levelling

I was recently gifted a large amount of 3D printing supplies by a very kind individual to whom I am very grateful.

Hidden in this treasure trove was an kit built Ender 3. The frame comes from an older printer but it has a creality main board, extruder, hot end and level probe. So it’s effectively an Ender 3.

It’s a capable printer, and I already have a Bambu, so I’m planning to clean the printer up and play it forward to a friend who want to try FDM printing.

The printer seems to be having trouble homing on the Z-Axis, and the auto bed leveling stops part way through.

When I try to home the Z it sometimes goes all the way up and stops, and sometimes goes part way up and stops. I can manually move it to the top using the control panel so it doesn’t seem like a physical jam. Other times it stops short of the bed. The latter is the most common,

When I try to do an auto-bed level it goes all the way to the bottom, doesn’t stop when the probe top touches the bed. It looks like it’s trying to push down further, the motor makes a tick-tick-tick noise and the gantry arm looks like it’s straining to push the novel into the bed.

I would guess that I should look at the Z offset, or maybe check if the level switch is actually triggering, but I don’t really know how to go about that.

Video 1
Video 2

Any suggestions would be welcome, but I’m afraid that I will need some instructions on how to get any information or to do anything, as most of my FDM experience is from Bambu printer which is more or less a black box that “just does everything, first time”. So I have zero trouble shooting skills. It just does it for me, which is both a blessing and a curse, I guess.

If it has an Ender 3 controller board then the firmware on the machine, which controls the sensing of end stops and probes, and it’s running Marlin firmware.
googling for “Marlin firmware testing end stops” would by my first place to look for videos to understand the process.
The M119 command is what reports the end stop switch status for Marlin.

Youve got a probe and an end stop. You shouldnt have both.

Check your printer cfg file and see what it is set to use. My guess its expecting the probe, and the endstop is physically stopping the Z from going down far enough.

I’m afraid that I’m normally a bambu user, so I’m not sure how to do any of that, they’re very good at isolating user from hardware. is there a tutorial that you can recommend that might help me to check?

There is a site dedicated to Marlin firmware :