Fuse burned
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you can see on the back photo that not only did the fuse melt, but also the board discolorized and the solder seems to have reflowed a bit where the fuse goes. I have a hard time imagining what could have caused this other than a massive spike from the PSU. What PSU are you using and can you maybe show how the wires that go into the board are connected on the PSU side?
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@oliof yes 1 minut
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(also the heater wires despite having ferrules look weirdly frizzy, are you sure there was no short just above the ferrules?)
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@oliof when I heated the bed to 80d it started to burn
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@sgk
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@sgk
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Well either way I would assume there is an issue with your bed heater that caused a massive short. Next to look at would be where the bed wires connect to the bed heater. Many simple printer designs forego proper strain relief there which causes the wires to work harden, then break, and likely short out. So the end of these wires are the next interesting thing to look at.
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@oliof yes
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@sgk yes?
also, it looks like the PSU was opened and modified in the past ... the yellow sticker is broken that usually warns you about this. At this point I would say you were glad to catch this before it caused a big fire ... but it does not look like a Duet specific issue.
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@oliof I just replaced the fan in the power supply with a larger one.
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@sgk
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So yeah that PSU is not fit for use anymore, as you lost all warranty on it and its now a liability. If anything happens, you will be personally held responsible.
Can you show the bed wires on the bed side?
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@oliof
by account I did not install a mosfet -
@sgk If your heater were rated at less than 15A (i.e. 360W on 24V, or 180W on 12V) you would not have needed an external mosfet. And if it would pull more, it would just have blown the fuse unless you get to very high wattage/resistances, i.e. a short.
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@oliof ha ok i have always had this 24v 350w bed
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@sgk  -
@sgk that would be fine, especially if you PID tuned it. Also it looks like the discoloration is on the VIN side, not the V- side where the PWM switching happens. This on board mosfet looks fine
but we might need a higher resolution picture of it.
Since this looks like a machine that ran well for a while, my money is still on an issue with the wiring on the bed side causing a short.
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@sgk yes, on your bed side picture you can see lack of strain relief, and already broken strands of the wiring.
This machine is a fire hazard.
Replace PSU and bed, and get someone with good knowledge of electrics and electronics to make sure the replacement is set up safely. Also make sure to add strain relief anywhere moving wires are attached to something (bed, hotend, and ideally board side as well).
You will also need to replace the control board as I do not believe its safe to continue using it even if you replaced the melted fuse.
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