TronXY X5SA Z position wrong after stop / start

[rh0042]

Hi all,
I'm new with Marlin, just upgraded from the TronXY Firmware to Marlin.
I have a TronXY X5SA with the following parameter V6_330_TITAN_TMC 1
I use the following GitHub [github.com] as this a great capability for TronXY 3D printer.

My problem is that when ever I stop and start my 3D printer I have to manually adjust the Bed to the correct level.
When I press Auto Home it move correctly but the Z position goes every time down for a couple of cm, when I press again Auto home it goes even more down (to the + direction) and not uses the sensor to adjust the bed level.

Does anybody has an idea what is wrong?

Thanks for help
Regards
Roland

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[zhanhongliau]

I just ran into this issue and after three days of scratching my head and reading countless posts I discovered that for some boards there's an issue with the Z probe initialization. Basically the probe registers as triggered on startup regardless of the actual state, which causes Z home to fail unless you manually trigger the probe before homing. You can verify this by turning on the printer and waving your hand in front of the probe until the light turns on, then from then on Z homing should work until you turn off the printer.

I posted another issue in the official Marlin firmware repo but to fix this you have to force the Z probe pin to pull up by adding

 SET_INPUT_PULLDOWN(Z_MIN_PIN);
 SET_INPUT_PULLUP(Z_MIN_PIN);

As the very first lines in the setup() function in Marlin/src/MarlinCore.cpp