Heatbed MK2a does not work

[uscachi@gmail.com]

Recently I buy a 3D printer: "Newest Hot 3D Printer Support 5 Filament". I was testing the 3D printer, and discovered that PCB heatbed MK2a is not working properly. When I turn on the heatbed by REPETIER software using the manual controls, the printer restart and the LCD shows min ERROR. The voltage provided by Sanguinololu to the heatbead is 12.2 V, the resistor connected to LEDs shows 986 ohm and the heatbed resistance was 0.2 ohm, apparently short circuit. Please let me know how to fix this problem, so I can print my first model. Thanks in advance.

[zhangxueyou]

When thermistor is open circuit, the LCD will display MINTEMP error, and the first line of LCD displays 0/0 of bed.
Is the resistor of thermistor 986 ohm when you unplug hot bed thermistor and test the resistance of thermistor on 2 ends of wire?

[uscachi@gmail.com]

Termistor is working fine, when I start the printer, LCD shows the room temperature (~27 C) similar to temperature shown by extruder termistor. When I turn on the heatbed by REPETIER using the manual controls the printer restart (turn off and on) then the LCD shows min error.

[zhangxueyou]

Please unplug the USB cable, and try to control the temperature on LCD screen.

[uscachi@gmail.com]

The termistor resistance is 68 ohms. Controlling the heatbed temperature by LCD (USB disconnected): I set the bed temperature to 40 C, then the printer restarted, and LCD shown Err: MINTEMP. Same results as described before by controlling the temperature by software REPETIER. Is correct that the heatbed resistance is 0.2 ohm? it looks like shortcircuit.

[zhangxueyou]

Maybe the way you test the resistance of hotbed is wrong.
You can try to re-upload the firmware.

[uscachi@gmail.com]

how to test the heatbed resistance correctly (may be: disconnecting the heatbed from the sanguinololu, then removing the 1 kohm resistor, and measure the resistance of heatbec)? How to re-upload the firmware? Thanks

[zhangxueyou]

Unplug the wire of hot bed from mainboard , and test the resistance at the end of wire.
You can refer to this page to upload the firmware:
http://geeetech.com/forum/viewtopic.php?f=20&t=16253

[uscachi@gmail.com]

I measured the heatbed resistance exactly as you recommended, but the resistances is 0.2 ohm, as i mentioned before. Anyway i will try to update the firmware...

[zhangxueyou]

Hi, what is your printer type and mainboard type? I can send you the correct firmware.