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Sanguino Runaway Hotend

Posted by jabba 
Sanguino Runaway Hotend
January 23, 2013 05:51AM
Hey all,

I bought a Max that was supposedly running and printing from someone. However, when it got to me it was a bit of a mess but did have a backup Sanguino 1.3a (at1284p) and I suspect it was because the board that was installed was fried (board marked as having bootloaded and firmware preloaded but could not connect through Pronterface and Audrino could not upload firmware). I wired up the other board which turns out had Sprinter pre-installed (assuming stock settings) and at least have proof of life and connect through Printrun and control the motors and access the temp sensors. The heatbed will heat up and turn off fine and the temp is reported correctly. However, the hotend starts heating as soon as the 12v power supply is turned on. Turning it off through Printrun/Ponterface does not turn it off. The sensor reports the proper temp, but I have no control over it - it is basically "always on" and the only way to stop it is to turn off the power supply. I have traced the wiring and verified it is correct.

Any ideas? I'm hoping since I'm relatively new to RepRaps that I might be overlooking something simple, like something that needs to be set in the firmware that can cause this condition, but logic kind of says if the heatbed is responding to On/Off then the hotend should also unless there is something shot with the board or something is shorted.

Thanks in advance!
Re: Sanguino Runaway Hotend
January 23, 2013 06:00PM

Since it came with a second board I was able to swap the Atmega 1284p chips to see if it was a bad chip. The problem still persisted, but it did allow me to rule the first board out as faulty because the chip I took from it and installed in the (mostly) working board had Sprinter firmware on it also and allowed me to connect to it. Again, the hotend just kept heating as soon as the power supply was turned when I hadn't turned it on in the software yet and would not stop no matter what I did. The heatbed operated fine.

So unless the same defect was in both chips (physical or bad firmware) I can rule out at microprocessor issue. I can't test with different firmware because I cannot upload firmware to it. No matter what I do (forcing a different com port, baud rates, modifying the boards.txt config, trying reset button a zillion ways with jumper on or off, etc) I get the stk500_getsync() error.

So, I guess I'm answering my own question... unless there is a firmware issue, which I cannot test because I can't upload firmware then it must be a hardware issue on the board itself. I am open to trying anything to get the firmware to upload or to fix the board but until then I think my only option is a new board.
Re: Sanguino Runaway Hotend
January 23, 2013 07:28PM
Well, if your processor seems okay and you don't see any troubles with the wiring or traces, my suspicion is that your mosfet is busted, as that's what is supposed to turn on and off the power to your heated bed. I'm not terribly familiar with Sanguinololu specs, so I don't know what mosfet to replace it with, but some googling/forum searching should yield info on that.
Re: Sanguino Runaway Hotend
January 26, 2013 03:44AM
Just swap the MOSFET (if you are familiar with Electronics and soldering) of Heat bed to the Hot End since Sanguinololu uses the same MOSFET for both Heat bed and Hotend

and check the Hot end control !

If it works fine you need to buy the MOSFET
Sanguino uses RFP30N06LE

Else you need to go further troubleshooting winking smiley
Re: Sanguino Runaway Hotend
January 26, 2013 09:59AM

unless there is a firmware issue, which I cannot test because I can't upload firmware

I think if your vendor didn't manage to upload a working bootloader it isn't too far streched to at least consider the chance of a misconfigured firmware.

You can measure the PWM voltage right on the ATmega pin. Find the track going from the ATmega to the MOSFET and measure the voltage with heater on and with heater off. Off should give zero volts, on should give close to 5 volts. A simple $15 voltage meter is sufficient.

With the ATmega removed you can even switch the MOSFET manually by touching the pin in the socket with 0V or 5V.

Generation 7 Electronics Teacup Firmware RepRap DIY
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