Bed Temp OK, but Heater Temp at 278C?...

Hi all,

I re-wired my prusa today, when i plugged everything back in, all components worked fine except for the heater temp reading... I'm using RAMPS 1.3, the reading is showing at 278C even it is at room temperature, however, reading of the bed temp was fine.

I've double checked and 100% sure not the problem with new wires and direct ohm measurement from both the bed and heater thermistors appeared to be correct, so I suspect something's wrong with the RAMPS board.

On the RAMPS board, T0 is supposed to be connected to the heater, and T1 to the bed. With the Arduino board removed, I then measured the resistance at each of the pair of pins... First from the working bed pins, T1, it measured 7K Ohm, then both T0 and T2 measured over 200M Ohm, and the first pin of each pair were connected.

Please can someone tell me what the problem is? Is there anything to do with the capacitors to the left side of the pins??

BTW, I'm using 100K thermistor.

Many thanks,
Adrian

Edited 1 time(s). Last edit at 04/14/2012 06:33PM by ahbtsang.

Looks like your thermistor table, have you selected the one for your thermistor?

Ollie

Yes, both the bed and extruder use 100k thermistor. It was working before i re-wired the whole thing. I tried plugging in the extruder cables into the bed pins and it read fine. Then when I unplugged all 4 cables, the bed reading was 0C but extruder was reading at 80C. So I think there must be something wrong with the 2 pins on my RAMPS board. I took the board out, double/triple checked whether any solders shorting the pins, but all looked perfect to me..

Any other ideas??

Many thanks.

Seems like the input has been damaged by connecting it to 12V. A common occurrence if the heater and thermistor wires get crossed or shorted together.

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[www.hydraraptor.blogspot.com]

nophead:

thanks. I just checked the the resistance on 4 cables (2 from thermistor, 2 from heater) they are not connected as I couldn't measure any resistance in any combinations.

The temp reading from ponterface fluctuates from 287 to 260+, once I unplugged all cables, the bed read 0C, and the heater read 80C, again fluctuated with +-20C

What can I do now to solve this?

Thanks very much for your help.

If the input is damaged you either have to replace the chip or find a spare analogue input, rewire the thermistor components to that and change the pin definition in the firmware.

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[www.hydraraptor.blogspot.com]

which chip is it I need replacing, sorry I don't understand what you meant by damaged input?? I hope it is not the arduino board..

To measure the temperature there is only a resistor, a capacitor and the Arduino input pin. Pretty hard to damage the resistor and capacitor, so most likely the input got more than 5V at some time which burns out that part of the Atmega chip and leads to false reading like you have.

If you unplug the Arduino can you still measure a difference between the RAMPS T0 and T1 inputs? If so it must be the capacitor, or a short on the board. If not it is the Arduino.

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[www.hydraraptor.blogspot.com]

nophead:

I removed the Arduino like you suggested, then I looked up the pins from the arduino to RAMPS..

#define HEATER_0_PIN 10
#define HEATER_1_PIN 8
#define TEMP_0_PIN 13 // ANALOG NUMBERING
#define TEMP_1_PIN 14 // ANALOG NUMBERING

so I measured the corresponding pins on RAMPS for 8 & 10, 13 & 14, I got around 110k Ohms from 13&14, meaning signal is transferring OK from the bed... Then when I measured 8&10 the reading was off the chart.. so I'm thinking there must be something wrong with the RAMPS. I tried switching over the plug, ie, bed -> heater and heater -> bed, I got the same result.

I measured the 3 resistors and capacitors, the resistors read the same.. I didn't know how to measure capacitance though although my multimeter although it can do it... but I measured their resistance, all 3 capacitors read 7k Ohms.

This RAMPS was the first solder I ever done.. and I admit that I kinda made a mess of it.. I'm guessing this could be the reason. I'm thinking of getting the RAMPS 1.4 to replace it since I have learnt better soldering skills now...

Is there any way to test whether my Arduino's chip is not blown? In case I am just wasting my money..

Edited 1 time(s). Last edit at 04/15/2012 04:28PM by ahbtsang.

Pin 8 and 10 control the MOSFETs that drive the extruder and bed heaters, so ignore them.

Try changing the TEMP_PIN_0 to 15 and plugging the extruder thermistor into T2.

#define TEMP_0_PIN 15// ANALOG NUMBERING
#define TEMP_1_PIN 14 // ANALOG NUMBERING


I made the changes as about to the firmware, then plugged in the thermistor to T2, I got exactly the same result.

Does this mean my Arduino is gone? But the bed temp is still reading correctly even I heated it up.

Many thanks.

the a/d channel may not be connected internal on that pin anymore. so the arduino is damaged at least for that pin, and probably any a/d reading on the port that pin was located on. so even though the rest of the arduino chip in question is mostly functional, some i/o pins have been over voltage and this has damaged the chip. I would invest in a new chip, if it is easily replaced. otherwise get creative with the i/o pins that are not used

here is a link to figure out what port the pins use

[www.arduino.cc]

[www.atmel.com]

I once had strange extruder heater temperature measurements when I had PID settings misconfigured with Marlin. Have you tried different firmware to eliminate any firmware problems as the cause?

I measured the resistance again.. this time I managed to find the ground pin for pins 13,14&15.

When plugging the thermistors to T0 and T1

Pin 13 - 110K Ohm
Pin 14 - 7K Ohm

Then when on T1 and T2

Pin 14 - 7K Ohm
Pin 15 - 110K Ohm

When no thermistors plugged in:

Pin 13 - 0 Ohm
Pin 14 - 7K Ohm
Pin 15 - 0 Ohm

Does this suggest something's wrong with pin 14 ie T1? But clearly T1 is the one giving correct temperature reading. Or is there something wrong with pin 13 and 15??

Many thanks.

Are you sure about those zero ohm readings? I can't see how resistance would decrease by removing the thermistor, that should leave an open circuit.

well, the readings from those pins went over 200M Ohm when the thermistors were unplugged, so I said 0Ohm.. in fact it should be very very large.

I am very lucky to found this thread. I have similar problem, T0 temperature stuck at 101.4c at room temp. But changing the TEMP_0_PIN from 13 to 15 seem to fix the problem. Using T2 now for instead of T0. But what does it mean? What should i do to get the pin 13 working again?

ahbtsang Wrote:
-------------------------------------------------------
> #define TEMP_0_PIN 15// ANALOG NUMBERING
> #define TEMP_1_PIN 14 // ANALOG NUMBERING
>
>
> I made the changes as about to the firmware, then
> plugged in the thermistor to T2, I got exactly the
> same result.
>
> Does this mean my Arduino is gone? But the bed
> temp is still reading correctly even I heated it
> up.
>
> Many thanks.

well, that time I was using RAMPS 1.3 and I knew I did a bad job soldering... I figured out that at some points the connectors was crossing hence getting this result. Now I upgraded to RAMPS 1.4and everything works amazing!

I'm using RAMPS 1.4 right now. Its funny because it worked fine earlier. I don't know exactly what i did to causes this. The last thing i did before it went crazy was to enable SDRAMP support. But i don't think this has anything to do with thermistor. Anyway, as long i am getting temperature reading at least from the T2 pin, i guess i am ok. Hope this has nothing to do with Arduino. Did you change your arduino?