Stuck on an issue with my Prusa I3 MK2
I purchased my printer on 7/21 and it arrived a few weeks later. I purchased the fully assembled version as I was a bit worried complications with a kit would be very discouraging as I am at best a tinkerer, with little background in assembly of things needing much precision.
Since my unit arrived it had been fantastic, all of my prints turned out amazing and it didn't matter if it was my own creations or something from thingiverse, but then while I was printing a bracket for a project I noticed things started going wrong.
I was looking at my octoprint readout from my desk and saw the bed temperatures were fluctuating wildly, and when I went to sit in front of the printer the display was doing the same. As the bed moved the readout would jump between 25-26c and the 60c it was supposed to be sitting at. It wasn't ramping up and down and using a cheap laser thermometer showed it was basically sitting consistent (though some areas of the bed varied by maybe 15 degrees) so my thought was a lose cable.
I opened the control box and the header itself was quite loose, and actually came off when I unclipped the wire for the bed. I just re-attached the cable directly to the pins with a dab of hotglue as a temporary fix... But the problem remained, so I removed the bed and checked the little probe there and it seemed as well attached as it could be to the bed (though a little off center from the circle). But after the troubleshooting, now it seems even though the bed still heats up, the readout just remains locked at 25c.
So I am left scratching my head and looking for some advice... Does this indicate that the problem is that little sensor under the bed? Or could the issue be with the RAMBO board? Is there anything else I should be checking? How do I get my replacement parts? And since the bed was removed and parts are likely going to need replacing, will I have to go through a lot of re-calibration to start using my printer again once it is repaired?
Any advice would be appreciated!
Re: Stuck on an issue with my Prusa I3 MK2
hi steven, welcome at the board !
you can use the board as a knowledge base, because here people come along with their issues and often find help by other users.
when you type in "thermistor got loose" at the search function, you'll find a few threads about the problem you've encountered.
this one for example....
dem inscheniör is' nix zu schwör...
Re: Stuck on an issue with my Prusa I3 MK2
Thanks for the reply, I took a look through the thread and followed the advice but it didn't seem to resolve my particular issue. It seems my issue was not that the thermistor came lose, but that it is defective?
So I removed the thermistor entirely and tried to check it with my multimeter but I was unable to get any reading at all. I was unable to find exactly what part number it is but purchased a replacement to at least TRY my theory.
The replacement I got was an NTC 3950 100K thermistor from Amazon (us) and wired it up with some new kapton tape. This seemed to work, as my temperature reading was no longer locked at 25c or jumping back and forth between 25c and 60c when the bed is moving. So this leads me to believe I just had a bad thermistor, but is my cheap replacement suitable?
But once this is sorted, I am still at a loss about what recalibration I need to do. With this (or a new Prusa) thermistor do I have to recalibrate anything with the heated bed? And with the bed having been removed a few times do I need to do more than just the z-height recalibration? I don't want to start doing any test prints without some input, because I really don't want to damage the bed!
Re: Stuck on an issue with my Prusa I3 MK2
inside the firmware, the default temperature sensor is defined as type 1.
#define TEMP_SENSOR_BED 1
/*------------------------------------
THERMISTORS SETTINGS
*------------------------------------*/
//
//--NORMAL IS 4.7kohm PULLUP!-- 1kohm pullup can be used on hotend sensor, using correct resistor and table
//
//// Temperature sensor settings:
// -2 is thermocouple with MAX6675 (only for sensor 0)
// -1 is thermocouple with AD595
// 0 is not used
// 1 is 100k thermistor - best choice for EPCOS 100k (4.7k pullup)
// 2 is 200k thermistor - ATC Semitec 204GT-2 (4.7k pullup)
// 3 is Mendel-parts thermistor (4.7k pullup)
// 4 is 10k thermistor !! do not use it for a hotend. It gives bad resolution at high temp. !!
// 5 is 100K thermistor - ATC Semitec 104GT-2 (Used in ParCan & J-Head) (4.7k pullup)
// 6 is 100k EPCOS - Not as accurate as table 1 (created using a fluke thermocouple) (4.7k pullup)
// 7 is 100k Honeywell thermistor 135-104LAG-J01 (4.7k pullup)
// 71 is 100k Honeywell thermistor 135-104LAF-J01 (4.7k pullup)
// 8 is 100k 0603 SMD Vishay NTCS0603E3104FXT (4.7k pullup)
// 9 is 100k GE Sensing AL03006-58.2K-97-G1 (4.7k pullup)
// 10 is 100k RS thermistor 198-961 (4.7k pullup)
// 11 is 100k beta 3950 1% thermistor (4.7k pullup)
// 12 is 100k 0603 SMD Vishay NTCS0603E3104FXT (4.7k pullup) (calibrated for Makibox hot bed)
// 13 is 100k Hisens 3950 1% up to 300°C for hotend "Simple ONE " & "Hotend "All In ONE"
// 20 is the PT100 circuit found in the Ultimainboard V2.x
// 60 is 100k Maker's Tool Works Kapton Bed Thermistor beta=3950
//
// 1k ohm pullup tables - This is not normal, you would have to have changed out your 4.7k for 1k
// (but gives greater accuracy and more stable PID)
// 51 is 100k thermistor - EPCOS (1k pullup)
// 52 is 200k thermistor - ATC Semitec 204GT-2 (1k pullup)
// 55 is 100k thermistor - ATC Semitec 104GT-2 (Used in ParCan & J-Head) (1k pullup)
//
// 1047 is Pt1000 with 4k7 pullup
// 1010 is Pt1000 with 1k pullup (non standard)
// 147 is Pt100 with 4k7 pullup
// 148 is E3D Pt100 with 4k7 pullup and no PT100 Amplifier on a MiniRambo 1.3a
// 247 is Pt100 with 4k7 pullup and PT100 Amplifier
// 110 is Pt100 with 1k pullup (non standard)
I think for the heatbed, the 3950 will be ok.
but it would be a good idea to do a pid calibration for the heatbed, at least it won't do any harm (but avoid oscillation of the temperature around the set value).
dem inscheniör is' nix zu schwör...
Re: Stuck on an issue with my Prusa I3 MK2
I had a very similar problem. For me it turned out to be an internal wire break for the thermistor, so as the bed moved the reading jumped around just like yours. It could have been broken from the factory or could have been me being a bit of a gorilla tightening down the zip ties. Either way, a new thermistor and wire fixed it.