Hi everyone! I’m new to this forum and new to 3D-printing!
I ran against a problem. My thermistor on the heated bed came loose (bad solder) and i connected it again. I also resolderd the plus on the heated bed again. But that’s where it went awkward; i didn’t switched off the power so i made a ground connection. I also replaced the heating element on the hot-end (wires came loose also) and since then the thermistor on the hot-end can’t measure any temperatures below 111 degrees. I switched the connectors and the problem stayed on therm1; always measuring 111 degrees or above… So what went wrong here? Is there a fault in the mainboard? And is it still useable? For all the rest it works fine, only temperatur-hot-end isn’t getting below 111 degree (measured); nevertheless, it does follow the setpoint, only not measured. Because i print only PLA (180+) it looks to me it doesn’t matter a lot, but i wanna know why it isn’t working correct… When i pull off the connector the temp also stays at 111 degrees. I couldn’t find any schematic that can help me, maybe i’ve blown a component?
I’ve searched again for a schematic and found one. Is there a possibility condensator C8 is blown up?
If you suspect C8, what voltage do you measure at the THERM1 connector without the thermistor connected? How does this compare to THERM2 in your setup?
If you shorted THERM1, you might have burned out R8 as another possibility.
Today i was able to measure some circuits on the board. Replaced R8 and C8, but didn’t solve the problem. Suspect i’ve blown up an input on the ATMEGA. Without the thermistors i measure 2.4 Volts on the THERM1. THERM2 is normaal, 4.95 Volts. Before R8 is measure 5 volts, so there is a voltage drop of 2.6 volts over R8; only able when there is an current over R8. With the plug disconnected the only component after R8 is the ATMEGA. Is there another digital input i can use, with right modifications in the firmware?
Is there a way to define another port on the ATMEGA2560? I’ve searched in arduino in tab pins.h for analog_pin_13 (PK5) to be able to chose another, non-used analog_input, to go around the blown up analog_in_13 without buying a new board. Couldn’t find it… Am I looking in the right direction?
That’s the idea. You would tell the firmware to use a different Analog In pin, then wire the thermistor, as well as equivalents for R8 and C8 to that input.
If you are determined enough, you might get this to work.
According to what I have read above, I believe you have used other type of thermistor. As the board READS temperatures well when heating up, the pin port works. So no PCB or connection problems… Maybe I am wrong…
Disconnect the thermistor cable from PCB and measure its resistance at room temperature. Then check if resistance matches the thermistor datasheet value. Then put your hand for a minute on the thermistor and repeat measurement. Resistance should match 36-37°C. This is the first step. Then check if you have the correct thermistor selected in Marlin.
In the worst case, subtrack (111-room temp) in Marlin…
The port on the ATMEGA2560 was blown up and had after failure an impedance that was too low: this occured a voltagedrop over the thermistor. Deleted the port and resolderd it with a jumper to an unused port of the ATMEGA. Also updated the firmware (to read temperature from another port) and the printer works fine now. Measured temperature, it’s 1.5 degrees offsett with a calibrated fluke-measurement.
