Fried hotend MOSFET - how to bypass?

Hi.

After having my reprap in a box for some time, I decided to start it up. Only problemwas that the MOSFET of the hotend had taken some damage. So when I turned on the heater it started burning.

"No problem, I will change to another MOSFET" I thought, I've got some IRFZ44N lying around. Well, not so easy, because the connector on the card has burnt also, the one on the source leg.

Now my question is how do I fix this? Can I just pull a wire from the 12V power supply directly to this leg? Do I need to connect it elsewhere? And how do I know I didn't burn anything else?

Thanks in advance for your answers.

Regards
fizz

Edited 1 time(s). Last edit at 04/28/2014 05:56AM by fizzman.

Replacing tracks with wires is entirely fine. Some even do this without having tracks damaged to allow higher currents.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Thanks for the answer.

I tried to go around the problem by adding a direct 12V connection via a wire, but it doesn't work.

Nothing happens with the hot end, it stays cool. The MOSFET isn't switching when I turn on the hot end in pronterface. I might have fried the board.

Or do you have an ideaof what else it could be?

Thanks

Check the signal pin. It should go to 5V. If not, you have to fix firmware and/or your ATmega chip.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Alright. Thanks, nothing happens with any of the pins when I switch on the hot-end.

I'll try with another MOSFET, but ultimately I think that the connections going to/from the MOSFET might be burnt from the small fire I had during the first start up. There might be some other connections that have burnt. See here how it looks, I have some extra wires soldered on there to try to connect, but nothing makes any difference.



I don't know how to read the circuit diagram on the Sanguinololu wiki, so I don't get which thing needs to be hooked up to what. Is there a circuit diagram for dummies somewhere, only talking about this MOSFET set-up?

Well, I thank you for your help in any case.

Best regards

Quote
fizzman
nothing happens with any of the pins when I switch on the hot-end.

I'll try with another MOSFET

If there's no signal voltage it's entirely pointless to try more MOSFETs. Just like changing light bulbs doesn't help when the light switch is broken.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Ok.

Thank you. I will then buy a new board.

And then I'll try to move the MOSFETs off the board. Feels more safe like that.

I wish you a nice weekend.

Quote
fizzman
I will then buy a new board.

How about fixing the signal trace? If you have a signal right in the ATmega pin but not on the MOSFET it shouldn't be too complicated to solder in a piece of wire to bridge the broken track.

If there's no signal in the ATmega directly, too, it's either a firmware issue or you need a new ATmega. On a Sanguinololu, the ATmega is replaceable.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

the mosfet parts where u soldier is gound Not 12volts. the heater 12V is direct from the powers supply the mosfet control the ground.

back of board

pin 1 signal
pin2 direct to connector to heater
pin3 board direct ground

when signal is send to pin 1, pin2 and pin3 is connected

Ok, thanks for this info, as you will see by both my explanation below and my soldering skills, I'm no expert in the electronics field.

I hooked it up according to the pic below.


Now there is a constant 12V on the heater, whether I switch it on or not. Did I misunderstand your pin 1, 2 & 3, or should it be like this?

Regards
Fizz

basically what y did is correct. and the board should work, u r saying there is a constant 12V on the heater, meaning the heater is activated or what, the heater is has a 12v supply and control by open or close ciruilt on the ground side. if your problem is heating up whether u switch it on or not then u have to recheck your soldering and the board again

Hi all.

It seems it's the ATMEGA that is not working. I get no signal change out from pin 19. So nothing is switching.

Well, I went and bought myself a new board in the meantime, I guess I'll have a spare if something else breaks. It would have been enough with a new chip I believe.

Thanks to you all for your help. I now have another problem, but I'll make a new thread for that...