M106 And Fan0

I think I made a boo boo…

Trying to use the fan pins to control an iot relay. I couldn’t get M106 to turn on the pin. While messing with it, I seemed to have shorted the Fan0 pin, now Fan0 is a constant 12v, and M107 just caused a M106 in the console to run. Seems really weird.

Not sure if I screwed the circuit up, the firmware is not setup for this or what is going on…

Fan pins on most control boards are ground side switching. To determine if you have an issue, you need be sure to use the ground pin of the pin pair in your testing. From the voltage pin in the fan pins pair, you will get a constant 12V as you’ve described.

If you have burned out the pin, there should be additional fan pins on your control board (Fan1, Fan2). For some boards, you need to modify the pins file to enable them for M106/M107.

What control board do you have? What IOT relay are you using? If you are using a commercial IOT relay, they usually take a range of voltages including 5V and 3.3V. You can control any pin on the board using M42, so you could have choices beyond fan pins.,

Well, I moved it over to Pin2 and it works, blown Pin0 circuit?

Assuming you tested using the ground side of the pain pair, then you probably damaged the pin.

Eeesh. At this rate I am going to have to buy a new board after just setting up everything the way I want it before I even start…

Thanks for your response

You don’t say what board you are using. If you have a Rambo or SKR Pro, then there is some protection on the pins, and they often survive mistakes. If you are using a Ramps board, then it is much easier to burn out pins. For pins set to output, any short to ground kills them.

It’s an SKR Pro V1.2

So how does a burnt out pin manifest itself? Weird things happen…

Pin0 is always 12v and M107, with or without Pin specifics returns an “M106 P0 S0”. Even if I enter M107 P2, it shuts off Pin2 but Pin0 stays energized and the console returns the M106 command

The fan pins have 12V (or 24V if you are using that) tied directly to the (+). The (-) side is what switches.

When off, the (-) side is floating, but there is a little LED circuit that pulls up the pin to 12V. So I would expect a multimeter to show +12V (if you have a 12V supply) when the pin is “off”.

When on, the (-) side is pulled to ground through a mosfet. It is a pretty big mosfet. A lot of things can happen with electronics, but I would be surprised if any of the voltages from 0-12V on that (-) pin could hurt the mostfet. There may also be a fuse that has blown. You should see 0V on the (-) pin when the fan is “on”.

A better guess is that something in the firmware, or how you’re controlling it is actually not turning it “on”. The circuit is pretty robust.

If you managed to short the logic pin on the other side of the mosfet somehow, then the MCU can still function with a broken output. Often, it takes out a bank of outputs (on atmel/arduino chips anyway, I haven’t seen an skr pop this way).

Interesting, I thought that the fan MOSFETs were smaller and an overcurrent draw would pop them like Orville Redenbacher. The FETs for the hotend or the heated bed are more robust, and you’d probably pop a (properly sized) fuse before those fail. Pretty sure I’ve seen fan circuits fail from overcurrent/shorting on many boards. I suspect that my MP3DPv4 paet cooling fan circuit has failed in this manner, since it currently will not turn off…

Since after sending a M107, even when I send an M107 P2, the console returns a “M106 P0 S0” and an ok, wouldn’t that show it is in the firmware somewhere? It is the stock firmware from V1, with a change on the touch probe pin that Ryan sent me for a possible board issue.

Ok, I am sure I am being dumb and don’t get this BUT here is what is happening

I am trying to add a second IOT, but…

P0 is a constant 12 V. When I enter M107 P0, the console returns a M106 P0 S0
When I enter M106 P1, nada, no voltage on that pin…
When I enter M106 P2, I get 12 volts
When I enter a M107 I get the same as above on the P0 pin

Any ideas what is going on or am I not getting this?

Thank you for any response

Something else, on P1 the LED doesn’t light up when I enter M106 P1 if that makes a difference