Thermostatic hotend fan issue

SpeedyDad

Duet2Wifi
Firmware: 2.02(RTOS) (2018-12-24b1)
Power supply: 24v

This is odd and has me scratching my head. My printers has hundreds of hours of printing. Up until now, the hotend fan was thermostatically controlled to turn on at 45. Now, it won't come on. I've verified that I have good continuity in the wiring. I have the following in my config file:

M106 P1 T45 H1

The fan is connected to Fan1 on the board. If I connect the fan to Fan2 on the board and configure it to P2 in M106, the fan just stays on no matter what the temp. Also, if I connect a voltmeter to Fan1, it constantly reads 24v yet won't power any fan hooked up to it (yes, I checked polarity to the fan).

What is going on here? I've seen reference to M950 in some posts. I've never had one. Needed?

Veti

set the fan to H-1 and see if you can turn it on via the web control.

the voltage will always be vin. the duet switches on the ground.

but if the fan is always on or always off, that could indicate a blown mosfet.

M950 is required for firmware version 3.

Phaedrux

Do you see any damaged little chips near the fan ports?

For example:
https://duet3d.dozuki.com/Wiki/Connector_and_spare_part_numbers#Section_Fan_mosfet

SpeedyDad

@Phaedrux said in Thermostatic hotend fan issue:

Do you see any damaged little chips near the fan ports?

For example:
https://duet3d.dozuki.com/Wiki/Connector_and_spare_part_numbers#Section_Fan_mosfet

I see a telltale black dot on TR9. Looks like I'm going to have to switch to always-on fans from now on with this printer. Oh well. Not the end of the world. I'll probably just have the always-on port switch on a relay to isolate the board from the fans.

davekeogh

I took popped one of the mosfets on one of my printers. Rather unfortunate grounding incident

Luckily I had another free PWM output so I was able to move over the connector.

I have also seen fans go weird about PWM after a while. 25mm fans I've gotten I've seen fail to start. So much so that I now put B3 to blip the fan for 3 seconds into my config.

Those mosfets are tiny and I was tempted to repair it (have a hot air rework station) but since my board is actually functional in its current state, unless I fry another I'm not going near it