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Actual hot end temperature is lower than the printer thinks

by leaftye

All indications are that the temperature is much lower than the printer thinks it is. It's not a fluctuation problem, it's just always too low and never getting close to the set temperature. I'm talking 50-70°C too low, and I have to crank the temperature setting to 260°C to get 190°C verified via thermocouple, and that's with the part cooling fan off. If I set it to 220°C, I can barely push filament through by hand, and the extruder skips, and my thermocouple says that's about 170°C, and that temperature again seems about right for the symptoms. The extruder can't move the filament until the temperature is set to 235°C.

Here's what I've done so far:
PID tune
Ground wire mod

My printer is a Monoprice Maker Select V2 with a Melzi V4.4 motherboard.

I think the problem has existed for months because I had been slowly ramping up temperatures while slowing print speed to minimize extruder skipping, but the problem has accelerated in the past couple of weeks.

I can't think of any changes I've made since the problem started. Just the usual bed cleaning, wiping and lubing the rods, etc. The most extreme thing I've done in that time is clean the extruder gear, so there's the possibility the thermistor wires were crushed.

I'm going to inspect the insulation on the thermistor and also check the voltage from the power supply, but I'm hoping someone knows what's going on because I'm just guessing now.

UPDATE 1: Inspected the thermistor from tip to plug with a watchmaker's loupe and the insulation, wire and tip looks good. I'm going to put some kapton tape on the heater block anyway.

UPDATE 2: Checked the resistance of the thermistor at 100°C and it's testing too low, so that may be the problem, and a replacement has been ordered.

UPDATE 3: New M3 thermistor still doesn't fix it. It's not as bad, but the temperature must be set to 260°C to get 210°C. Checked the wiring from the thermistor to the motherboard for shorts, and found none. Also double checked the resistance of the thermistor, and it read the appropriate value for room temperature. Finally, I checked the voltage at the power supply. The input is 125V AC, and all outputs are 12.15V DC. Replacing the wiring from the thermistor plug to the motherboard didn't fix it either, but it allowed the temperature to get to 210°C even though the firmware "only" said it was 250°C. I'm going to try adding a wire shown as the blue line in the attached diagram. If that doesn't fix it completely, but improves it, I'll install a hotbed mosfet for the hotend.

hotend monoprice_makerselect temperature Wanhao_Duplicator_I3
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Y-plate upgrade, lightest

by gamekorp

Cheapest you'll ever get em. Limited time. Plates won't be made anymore, this is the best of the leftovers (still good!)
Works on V2.1 and PLUS

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Fixing burnt out hot bed connector

by lindsaytcrawford

Hi there, I had my hotend connector burn out. I noticed a smell while it was printing and that the bed temperature wasn't getting to 105 anymore. Set the bed down to below ambient and managed to complete the print.

Now I just need to know the best way to fix it. It seems they don't use the correct colour wires to the bed, red in the picture is connected to the pad marked as negative (I guess it doesn't really matter). The pad that burnt out is actually the positive, which seems to be the common (switching on and off of the bed seems to be regulated on the negative). Since the burnt out pad is common positive, is the best (and probably easiest) solution just to wire this directly into the positive 24V out of the psu? I'd put a new connector on the board as well but just use the negative on it since the positive pad looks too damaged.

And yes, I know an external mosfet is a better long-term solution, just want to get it working now.

Thanks in advance!

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Any plans for linear rails for i3

by JazzyJock

Hi guys and gals. Eventually after a long time I got my y-carriage plate cut and while I'm about to fit it I'm aware that my bearings are also running a bit rough. So as I have to replace them I was wondering if anyone had done a Linear rail replacement on the i3. If so what was needed. I'm not the most techy person so any help would be appreciated.


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Which mods you have on your 3d printer

by slanwar

I did a few mods on my Maker and the last one I replaced the Melzi board with ramps 1.4 plus I installed a inductor sensor. I installed as well a buildtak system.

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