I have just built this printer and am anxiously awaiting getting to try it out. However I’m having an issue with the hotend thermistor, or rather I think with the board itself. In Repetier the extruder temp hovers around 203 degrees C when its actually room temperature. Haven’t tried actually heating it yet. I’ve been searching all around and have come up with a few things to diagnose the issue.
Swap the bed and extruder thermistor wires. Result is extruder still shows 204C, bed temp reading now goes up if I hold the hotend with my hand (presumably thermistor is installed OK).
Unplugging extruder thermistor should give 0C reading. But mine still reads 204C.
Resistance of extruder thermistor when unplugged reads 115kOhm at the plug.
From this I’m thinking there is a problem with the therm1 pins on the board. Are there any spare pins I could connect it to to see if it works. Understanding I’d probably need to tweak the firmware. Otherwise what are my options?
From the posts on here Velleman seem to have had a lot of problems with poor soldering on the board. I personally had to resolder the USB socket as one leg was not soldered, and I had an intermittent fault with one of the stepper motor ICs which was also down to soldering.
If you feel confident enough to tackle it yourself, inspect the board carefully and resolder anything that looks like it needs it. Otherwise send the board back to Velleman for a replacement.
Thanks for the response. I have gone through most of the other tests and things seem to be working correctly except for monitoring extruder temperature. I’ve swapped the pins in the firmware for the therm1 and the bed for now so I can continue testing that everything else is working. Pumped to see this squirt out some melted plastic for the first time!
I’ve had a look with a magnifying glass (albeit a poor one) and I don’t see anything particularly wrong. I followed a suggestion to someone else about checking resistance between the first pin on the thermistor port and the 5v pin for the expansion board. From therm2 which is working correctly I’m seeing 4.7kOhms which was correct according to the post, but Therm1 was showing 1.7kOhms. I’m no electronics engineer (and this is my first electronics project as well), but wouldn’t this mean either a resistor is not functioning properly or trace allowing a partial bypass of the resistor?
There is a fishy looking solder job on the 4701 resistor below the therm1 connection. I’ll try to get a high-res image posted tonight for possible comment if it could be related. I just this last month so I’m hesitant to start re-soldering it myself.
The input circuit for both thermistors is just a resistor to the 5 volt rail and a capacitor to ground. With either thermistor unplugged you should measure 4.7k from the input pin to the supply rail, and when power is applied 5 volts across it’s 2 pins.
You could also try shorting the 2 pins together and seeing what Repetier reports.
OK, so I finally had a chance to check it out again. I’m getting 5v measured across the pins on the thermistor connect that works and 0.4v on the other one. Also when I short the pins on the good one it goes from 22C (ambient temp) to 763C. On the one that doesn’t work it goes from 204C to 763C. So the response of the controller appears good from my inexperienced eyes, but there definitely something wrong with the 0.4v.
That’s the response that i would expect from Repetier.
There’s only a few possibilities - faulty capacitor (very leaky) - faulty resistor (high value - bad soldering) - faulty microprocessor. How you proceed is up to you - try to fix it, or send it back.
Personally I would resolder R8 first, if that doesn’t work remove C8 and try again. If neither of those work then it’s most likely a damaged processor and the board needs to be sent back.