[BUG] Intermittent Z homing failure on MKS TinyBee with TMC2209 standalone after successful first home

[daniel-scatigno]

Did you test the latest bugfix-2.1.x code?

Yes, and the problem still exists.

Bug Description

Bug Description

Testing latest bugfix-2.1.x on MKS TinyBee (ESP32) with TMC2209 drivers in standalone mode.

Z homing is unreliable in my Marlin build:

• First G28 Z may succeed
• Subsequent G28 Z commands may fail intermittently with mottors off
• Z endstop is detected correctly (verified repeatedly with M119)
• Homing reaches endstop and performs bump sequence, but failure can occur afterward
• Behavior persists after testing with HOMING_BUMP_MM set to zero
• ENDSTOP_NOISE_THRESHOLD changes did not resolve issue
• Driver safety / monitor features disabled
• TMC2209 are used in standalone (not UART)

Important:
Using Makerbase MKS TinyBee firmware on the same hardware, wiring, endstops, drivers, and mechanics, repeated Z homing works reliably.

This suggests a bug or configuration interaction in bugfix-2.1.x specific to this setup.

Observed debug output includes:
Home Fast: -450.00mm

(appears to be 1.5x Z travel and may be expected, but included for reference)

Hardware

• Board: MKS TinyBee
• Drivers: TMC2209 standalone
• Printer: Core Cartesian custom build
• Z endstop: mechanical switch
• No Z probe
• Z travel: 300mm
• PSU: 12V

Expected behavior

Actual behavior

Bug Timeline

No response

Expected behavior

Repeated G28 Z should home reliably every time.

Actual behavior

First homing may succeed, subsequent homing can fail intermittently with motors off.

Steps to Reproduce

No response

Version of Marlin Firmware

FIRMWARE_NAME:Marlin bugfix-2.1.x (Apr 28 2026 18:33:03)

Printer model

No response

Electronics

No response

LCD/Controller

No response

Other add-ons

No response

Bed Leveling

None

Your Slicer

None

Host Software

None

Don't forget to include

• A ZIP file containing your Configuration.h and Configuration_adv.h.

Additional information & file uploads

Config.zip