PanelDue checksum errors when heater on or hand near PDue cable

Scachi

Can someone explain what is/was happening here and if I did something stupid by solving it the way I did ?

Issue: a lot of checkum errors showing up on PanelDue
Solution: using a shielded cable and connecting the shield to "-" of the 4-wire port of the PanelDue

More details:
Modified Rat Rig V-CORE (corexy),
Mods:

3xZ threaded rods via belt driven by single Z-Stepper (based on the mod at thingiverse from Phaedrux https://www.thingiverse.com/thing:2651649),
4xZ V-Slot (added 2xZ Vslot each with 3 wheels to the front)
custom hotend mount https://www.thingiverse.com/thing:3637202

I am using a PanelDue 4,3 inch, Firmware Version: 1.22.1

with a Duet 2 WiFi:
Firmware Name: RepRapFirmware for Duet 2 WiFi/Ethernet
Firmware Electronics: Duet WiFi 1.02 or later
Firmware Version: 2.03 (2019-06-13b2)
WiFi Server Version: 1.23
Web Interface Version: 1.22.6

Silicon Bedheater 24V 450W, connected via ssr , both from filafarm
A single powersupply 600W 24VDC for everything (duet+heater) (Chargery S600 Plus, spare one from rc hobby)

I was getting a lot of checksum errors on the PanelDue as soon as the silicon bedheater reaches 60°C or more.
Also, with or without bedheater on, putting my fingers near the PanelDue 4-wire cable caused those checksum errors too.

I tried different things..
my x&y endstops are near one of my corexy stepper motor (y connected one).
Twisting the endstop wire pairs was helping a bit for the bed heater I think, but did not solve the problem with me getting near the cable.
The baudrate setting (config.g + PanelDue settings) didn't matter at all.
Grounding all three steppers (x/y + z) to gnd of the power supply didn't solve/change the issues.

It looks like using a shielded cable (I used a spare usb cable from a printer) and connecting the shield to the - of the 4-wire port of the PanelDue solved the checksum error completely.
I can now use the heatbed at any temperature and touch the paneldue cable without causing any checksum errors.

Any ideas why this solves the checksum and what the real problem is ? Is this safe to do ..shield to - of panel due ?
Do I need to or should I ground all steppers + the whole CoreXY frame ?

@scachi said in PanelDue checksum errors when heater on or hand near PDue cable:

olution: using a shielded cable and connecting the shield to "-" of the 4-wire port of the PanelDue

Presumably the PanelDue itself has no ground connection, and in that case I would rather ground the shield of the cable at the Duet side.

dc42

My guess is that the pulsing heater PWM voltage is leaking through to your un-grounded printer frame, and the PanelDue cable was picking it up from there. My usual recommendation is to connect the printer frame to mains ground, also connect the negative PSU output to mains ground. That would probably have solved the problem.

What you have done is to shield the PanelDue signal wires from the printer frame. That's fine, but should not be necessary if the frame is connected to the negative PSU output.

Scachi

Thank you for your answers. I will ground the frame plus the negative psu output like dc42 said.