I have just completed my build and ran through all the calibration perfectly.
I was just about to start my first print when I noticed that the Heated Bed Temperature was showing as 105.4o Deg C. It was working perfectly during calibration, showing 50 Deg C after a couple of minutes.
If I remove the Heated Bed connector from the control board the temperature still shows as 104.40 Deg C.
If I swap the two Thermistor cables around I can prove that the Heated Bed Thermistor is working. Temperature shows as room temperature in the Extruder Temperature display in Repetier with either Thermistor connected to Therm 1.
I have done nothing apart from setting all the home positions and fiddling with the heated bed levelling.
there have been a couple of similar issues lately. From your description, unfortunately an error on the controller board (e.g. ATmega’s analog input) is likely. In other words, the chance you’ll be able to fix this quickly yourself is slim. However, I’d recommend a few more tests, just to be sure.
Do you have a standard resistor at hand, maybe even 100 kΩ? Additional smaller values would also help. When connected to either THERM input, room temperature should be indicated, with rising temperatures for lower resistance values.
Alternatively, connect the working hotend thermistor to the heatbed input and start heating the bed while observing the indicated temperature. Does it change while the bed gets warmer? Keep in mind that you’ll need to manually stop the heater after some time, since the temperature regulation doesn’t work this way.
As for the board: you can visually check the solder joints and some of the circuit paths between the THERM connectors and the ATmega. The pins used for those inputs at the ATmega are 83 and 84. Are there any irregularities?
Cheers,
kuraasu
(edit: “bed” instead of “hotend”, of course. Sorry for the confusion.)
I have tried connecting the Hot End Thermistor to the Hot Bed connector on the control board and I still get a reading of 105 Deg C.
If I connect the Hot Bed Thermistor to the Hot End connector on the control board I can start heating the bed.
I am assuming the ATmega is the chip with a large number of pins (around 15mm by 15mm).
The right pin on the hot bed connector is connected to the 8th pin down the left side of the chip.
The left pin on the hot bed connector is connected to a number of pins on the chip.
I cannot start heating the bed. If I connect the Hot End to the Hot Bed thermistor I can start heating the Hot End (extruder) and the temperature displayed against the Hot Bed climbs from 105 deg.
So it looks like the control board is seeing a change in temperature but it has a starting point at 105 deg.
I suppose I could try setting the Hot Bed temperature higher. Say 105 - room temperature + 50. Do you think that might work?
sorry, there was an error in my previous post. But I think you already got it right:
yes, that was the idea.
[quote=“etlprws”]I am assuming the ATmega is the chip with a large number of pins (around 15mm by 15mm).
The right pin on the hot bed connector is connected to the 8th pin down the left side of the chip.
The left pin on the hot bed connector is connected to a number of pins on the chip.
Sorry, I do not know how the pins are numbered.[/quote]
Correct, that’s the “brain” of the board. There’s a single marking in one corner, that’s where you start counting, counter-clockwise. Each side has 25 pins. The fourth side starts with pin 76, so 83 is, like you already found out correctly, the eighth pin there. There’s a good schematic at Arduino’s website.
The second contact from the THERM input is simply a ground connection, that’s why there are several routes to the ATmega.
I’m not really sure. The input does not seem to be completely defect, since the temperature measurement still reacts when changing resistance (i.e. temperature of the connected thermistor). I’d say it could be worth a try to reload the firmware, maybe it’s just the thermistor reference table that’s faulty.
But I’m also open for other suggestions. Setting a temperature offset perhaps, after checking that the temperature is really just shifted and not rescaled?
There’s a chapter on updating the firmware in the manual, perhaps you already read it?
It seems it is not just an offset but I have found that by setting the Hot Bed to 108 Deg it reaches and maintains 50 Deg. I have checked by swapping the thermistor connectors and checking on the Hot End reading.
I am now actually printing something! It is a bit rough and ready but it is actually printing.
I will try the firmware tomorrow. It is odd that the control board is detecting the resistance change, just not from the correct starting point and or the right scale.
so, did I get this right? 105.4 °C (shown) is room temperature, say somewhere between 20 and 25 °C (real), but 108 °C (set/shown) equals 50 °C (real)?
Cheers,
kuraasu
PS: right next to the THERM input, there’s a capacitor and a small SMD resistor. Could you post (a link to) a high-res photo of those, especially of the resistor?
In some of the pictures there seems to be a bit of discolouration (slightly yellow). This is only in the pictures and due to the lighting. The two components look ok to me.
one final test from my side: with the board unpowered (both 15 V and USB, to be on the safe side), could you measure the resistance between the THERM2 socket, right pin (towards the “T” in “THERM2”) and a 5V pin, e.g. the one in the extension connector area on the right edge of the board?
That’s strange - approx. 4.7 kΩ would have been the “correct” value (I double-checked it on another board). Also, your photos show the right resistors (R7 and R8, “4701”).
From your observation about the indicated temperature being too high on THERM2, I would have expected a higher resistance there, not a lower one. That would have at least explained the difference in the temperature measurement, providing a basis for the aforementioned offset (or recalibration).
On THERM1, the value should be at 4.7 kΩ in any case, so either there’s something wrong with your multimeter, or, which unfortunately at this point becomes more and more likely, there’s really a defect in the controller board.
So, next step would then be to contact Velleman (or your distributor) about this issue.