Heat Bed died in the middle of 17 hr part

[msmith358]

I am running a Geeetech i3 Pro B with an aduino 2650 RAMPS 1.4 board. I just purchased the printer, and have only printed a few calibration parts. There were two occasions where the bed heat ran away unexpectedly mid way through the part. (30 min parts). I got everything working nicely, and decided to run my first large part. At 15 hours into the 17 hour part, the bed stopped heating and was unresponsive to commands. I could see the commanded temps on the LCD, but the bed would not heat.

I have since reset the machine, reset firmware, checked the wiring. There is no response. Oh, No electrical burn smells either...

Please help.

[zhangxueyou]

Hi, msmith258
Please tell me where the firmware you used comes from.

[msmith358]

It was the firmware emailed to me from this forum when posting the make and model.

[zhangxueyou]

Please take a picture of mainboard.

[abulafi]

After printing several parts successfully, I started printing some part with 45° heat bed. After 1 hour the temperature of the bed started to raise indefinitely until reaching 125°. The LCD was showing the upper limit correctly and reading the sensor as well. I tried to set the temperature of the bed without stop printing using the LCD, but with no use. Finally I had to remove heatbed wire from the ramps to prevent burn out.

Any ideas to troubleshoot the issue?

[zhangxueyou]

After printing several parts successfully, I started printing some part with 45° heat bed. After 1 hour the temperature of the bed started to raise indefinitely until reaching 125°. The LCD was showing the upper limit correctly and reading the sensor as well. I tried to set the temperature of the bed without stop printing using the LCD, but with no use. Finally I had to remove heatbed wire from the ramps to prevent burn out.

Any ideas to troubleshoot the issue?

Sorry for replying you so late.
Please unplug the wire of themistor connected to mainboard. Use a multimeter to test resistance of hot bed thermistor under normal temperature.

[abulafi]

Sorry for replying you so late.
Please unplug the wire of themistor connected to mainboard. Use a multimeter to test resistance of hot bed thermistor under normal temperature.

Nope, the thermistor was OK since the LCD was showing and updating the rising temperature. It was related to the poor MOSFET which was dead short.

[msmith358]

I used a hair dryer to blow heat on the bed as a quick test to check response before pulling apart the zip ties and cable management. Turns out the thermistors are working. I bought a replacement RAMPS board and swaped it out. It turns out the RAMPS Board was faulty.

[zhangxueyou]

Sorry for replying you so late.
Please unplug the wire of themistor connected to mainboard. Use a multimeter to test resistance of hot bed thermistor under normal temperature.

Nope, the thermistor was OK since the LCD was showing and updating the rising temperature. It was related to the poor MOSFET which was dead short.

How do you mount the mainboard on Acrylic board?

[abulafi]

How do you mount the mainboard on Acrylic board?

I know what you mean. I couldn't mount the board so that the MOSFET's are nearer to the blowing fan, doing that will block the access to the USB terminal.
And since the design of the RAMPS board is too tight to mount a heat sink on the MOSFET's, I decisded to make an extension using thick wires, taking the heat bed MOSFET out and mounted a heat sink on it.