@razrudy Ok, so I'll connect both and give it a shot and see what the results are and will report back.

Re: Duet 3 6HC Output_0 always on

Today I received my replacement board from Filastruder. Upon removing it from the antistatic bag and doing a visual inspection I see some type of liquid/fluid around one of the components. I've added pictures below.

@Phaedrux thank you - I've linked them to this thread.

@razrudy the mosfet looks fine. No physical damage, bulges, loose connections etc.

@razrudy That was my conclusion as well but per Filastruder I have to have a mod/admin approve to get an RMA issued.

I've tried this with seperate supplies, the same supply and new power supplies to no change in the problem I'm experiencing so I don't think it's related to the power suppl(y/ies).

@razrudy I don't think this is config related as replacing my config with a default one, or not one at all the same behavior exists.

@fcwilt I don't know. Could that be related to the fuse that I replaced that was loose at the start that was causing the bed to power on and off randomly? Or something else?

@razrudy With the thermistor connected and the bed connected, it still heats. It goes into fault state but power is still being supplied on OUTPUT_O regardless which is what has me scratching my head. Removing either lead positive or negative from INPUT_0 stops the power that's being output for OUTPUT_0 as expected.

@fcwilt My config, right now is a default/stock one from RRF's configurator that I've not reconfigured as I replaced/reflashed firmware/image etc to troubleshoot this. This is was my config prior

; Configuration file for Duet 3 (firmware version 3)
; executed by the firmware on start-up
; GCode Dictionary: https://duet3d.dozuki.com/Wiki/Gcode
; General preferences
G21                                                             ; work in mm
M555 P2                                                         ; Set Marlin-style output

G90                                                             ; send absolute coordinates...
M83                                                             ; ...but relative extruder moves
M550 P"Duet 3"                                                  ; set printer name
M669 K1                                                         ; select CoreXY mode

; Drive Mapping/Config
M569 P0.0 S0 D3 V5 H5                                        ; Drive 0.0 E goes forwards   / Extruder
M569 P0.1 S1 D3 V5 H5                                        ; Drive 0.0 X goes backwards  / Left
M569 P0.2 S1 D3 V5 H5                                        ; Drive 0.1 Y goes backwards  / Right
M569 P0.3 S1 D3 V5 H5                                        ; Drive 0.2 Z goes backwards  / Left Z
M569 P0.4 S1 D3 V5 H5                                        ; Drive 0.4 Z goes backwards  / Right Z
M569 P0.5 S1 D3 V5 H5                                        ; Drive 0.5 Z goes backwards  / Back Z - triple Z
M584 E0.0 X0.1 Y0.2 Z0.3:0.4:0.5                                ; set drive mapping - triple Z
M906 X800 Y800 Z800 E800 I30

; Leveling
M350 X16 Y16 Z16:16:16 E16 I1                                         ; configure microstepping with interpolation
M915 X Y S2 F0 H200 			; X / Y Axes
M566 X900.00 Y900.00 Z60 E3000           ; set maximum instantaneous speed changes (mm/min)
M201 X2500.00 Y2500.00 Z100.00 E2500.00        ; set accelerations (mm/s^2)
M203 X12600 Y12600 Z900 E25200      ; Maximum speeds (mm/min)
M204 P3000 T3000
M208 X0:300 Y0:300 Z0:330                                             ; set axis min & max for X/Y
M92 X99.60 Y100.35 Z1604.11 E419.6
M84 S30 												        ; Set idle timeout

; Endstops
M574 X1 Y1 S3                                                   ; configure sensorless endstop for low end on X & Y

; Bltouch
M950 S0 C"io7.out"                                              ; create servo pin 0 for BLTouch
M558 P9 C"^io7.in" H5 R1 F800 T6000 A5 S0.02 B1                 ; set Z probe type to bltouch and the dive height + speeds
M671 X-25:335:152 Y40:40:350 S2                                   ; leadscrews at left (connected to Z) and right (connected to E1), Rear Z is E2, set max correction to 3.5mm (S)
M557 X20:280 Y20:280 S20                                        ; define mesh grid (subtracting values for mesh to account for Z probe offset in X/Y)
G31 P25 X-19 Y13 Z1.980                                        ; set Z probe trigger value, offset and trigger height


; Mesh Bed Compensation
M376 H5									                        ; Set taper height 10mm

; Thermistors
M308 S0 P"temp0" Y"thermistor" T100000 B4138                    ; configure sensor 0 as thermistor on pin temp0 / Bed
M308 S1 P"temp1" Y"thermistor" T100000 B4725 C7.06e-8           ; configure sensor 1 as thermistor on pin temp1 / HotEnd

; Heaters
M950 H0 C"out0" T0                                              ; create bed heater output on out0 and map it to sensor 0 / Bed
M950 H1 C"out1" T1                                              ; create nozzle heater output on out1 and map it to sensor 1 / HotEnd

; Bed
M140 H0                                                         ; map heated bed to heater 0
M307 H0 B0 R0.292 C478.8 D1.12 S0.90 V23.7                      ; disable bang-bang mode for the bed heater and set PWM limit

; Hotend
M307 H1 R1.523 C339.7 D6.57 S1.00 V23.9
M570 S180 H1 P10 T15                                            ; Hotend allows 10sec for anomaly, permits 15deg excursion, abandons print after 180s

; Fans
;   Part Cooling
M950 F0 C"out2" Q500                                            ; create fan 0 on pin out2 and set its frequency
M106 P0 C"PartCoolingFan" S0 H-1                                ; set fan 0 name and value. Thermostatic control is turned off

;   Hotend
M950 F1 C"out3" Q500                                            ; create fan 1 on pin out3 and set its frequency
M106 P1 C"HotEndFan" S1 H1 T45                                  ; set fan 1 name and value. Thermostatic control is turned on

; Tools
M563 P0 S"E3DHotEnd" D0 H1 F0                                   ; define tool 0
G10 P0 X0 Y0 Z0 R0 S0                                           ; set tool 0 axis offsets

; Custom settings are not defined
M575 P1 S1 B57600                                               ; enable support for PanelDue
M911 S10 R11 P"M913 X0 Y0 G91 M83 G1 Z3 E-5 F1000"              ; set voltage thresholds and actions to run on power loss
T0                                                              ; select first tool

; FEEDRATE CONVERSIONS
		; 20mm/s = F1200
    	; 35mm/s = F2100
		; 50mm/s = F3000
		; 70mm/s = F4200
		; 100mm/s = F6000
		; 120mm/s = F7200
		; 133mm/s = F8000

It keeps being flagged as spam.

@fcwilt Correct. Anytime there is power applied to OUTPUT 0 POWER IN then OUT 0 will output power as noted by my bed led lighting up.

Having power on VIN or not doesn't change that. Its why in my testing I disconnected the SBC that had the config and disconnected any and everything else to reproduce the issue with minimal things connected.

Here's the same with VIN and OUTPUT Power IN showing power being supplied - when not being told to do so by any config.

@razrudy Ok, so I'll connect both and give it a shot and see what the results are and will report back.

Fair point, but this is the same behavior that it does when everything else is connected. What would be a good/valid test to perform?