@dc42
I've taken the board out and turned it over to find this:
It looks the the Bed - pin of the screw terminal has failed. The 'corroded' pin popped off with a light touch and the terminal itself doesn't feel secure (flexes easily). There is a slight bubble there - likely due to heat from the short.
Looks like the screw terminal will need to be replaced, but the mosfet is likely to be ok?
Fixed by changing the bed settings to:
; Bed
M305 P0 T100000 B4185 R2200 ; Set thermistor + ADC parameters for heater 0
; Heaters
M307 H0 B0 S1.00 ; Disable bang-bang mode for the bed heater and
M307 H0 A153.5 C555 D0.3 B0 ; Heatbed
M307 H1 A278.6 C158.2 D3.8 S1.00 V24.2 B0
; set PWM limit
; Bed
M305 P0 T100000 B4138 R4700 ; Set thermistor + ADC parameters for heater 0
M143 H0 S80 ; Set temperature limit for heater 0 to 80C
; Hotend
M305 P1 T100000 B4725 C7.060000e-8 ; Set thermistor + ADC parameters for heater 1
M143 H1 S280 ; Set temperature limit for heater 1 to 280C
The config was used previously with a Duet Wifi - bed temp reading was accurate with it.
Is there any configuration needed around the bed temperature sensor to get it accurate? I've just wired up a Maestro and it's reporting the bed to be around 10C when the ambient temperature is 25C. I'll need to check hotter temps, but it was around 62C when set to 50C (if I remember correctly).
@3ddevil I have no idea about rework (or lack there of). The pin and solder are all crumbly - it took minimal pressure (with fingers) to convert into dust. I don't recall anything odd looking with the board when installing, although that was in January (so I might have forgotten). I'm sure I would have noticed if it looked like it did in the pics above - that doesn't look healthy at all.
@EasyTarget Thanks for the annoted pic. Will help with troubleshooting (should I have any issues in future)
@dc42
I've taken the board out and turned it over to find this:
It looks the the Bed - pin of the screw terminal has failed. The 'corroded' pin popped off with a light touch and the terminal itself doesn't feel secure (flexes easily). There is a slight bubble there - likely due to heat from the short.
Looks like the screw terminal will need to be replaced, but the mosfet is likely to be ok?
@EasyTarget said in Duet 2 Wifi - Bed no longer heating:
There are other things that could be tested, in particular the gate and source voltages of the mosfet to verify that it is receiving the gate signal, and that it's source is properly grounded.
How do I check that?
I don't think it's a wiring issue - it's been functioning fine for several months before failing. The wiring wasn't changed in that time. I've connected the bed to a different board and it works (using the same wiring and powersupply)
@EasyTarget Thank you for your help!
As I got the board in January, I suspect it's likely out of warranty. The external mosfet is likely going to be the easiest (and fastest) route for me.
Wonder if Duet offer a repair service...
@whosrdaddy Thanks!
@EasyTarget
Looks like the mosfet has failed then. 
24V on both terminals when bed is off, and 24V on both when bed is on.
I have a multimeter - would this be in AC or DC (voltage) mode?