Inaccurate Heat Bed Temp Display

[mpyr6]

I have printed with my Rostock a few times now but recently when the heat bed is heating the temperature will jump around from 61 degrees to 85 degrees and then back down to 61. It seems as though it reads the accurate temperature and then pops back to the wrong temp. When I turned on the printer today the hot end and heat plate were a mere .5 degrees off from one another but now it is fluctuating between 120 to 140 degrees on the display. This started once I ran the PID Test since I just installed the fan shroud and fan. I have confirmed that the heat plate is not hot and has not been receiving any power since the issue occurred. Is there a firmware issue or what could cause these inaccuracies?

Thanks!

[Eaglezsoar]

I have printed with my Rostock a few times now but it seems as though every once in awhile as the heat bed is heating the temperature will jump around between 61 degrees to 85 degrees. Currently, it is sitting at a toasty 97 degrees on the display but is cool to the touch. Is there a firmware issue or what could cause these inaccuracies?

Thanks!

I would suspect the wiring to the thermistors first.
If you have a Volt-Ohm-Meter you need to first need to check the resistance of the thermistor at room temperature and it should read approximately 100K
I would pull the correct thermistor from the Rambo and use to fine wires to insert into the thermistor connector and measure the resistance that way.

If the resistance measure OK at this point, jiggle the thermistor wiring to see if the value changes while hooked to the meter.
Any noticiable variation indicates a problem with the wiring.

If the thermistor does not read 100k at room temperature the either the wiring is bad or the thermistor could be bad.
Best of luck in troubleshooting.

[mpyr6]

Ok, so since I don't have a Volt-Ohm Reader at my disposal this moment I decided to switch the hot end and bed connector on the board and the same thing is happening where now the hot end is reading hot. So I can conclude the issue is between the wire and the Thermistor. I will have to dive deeper when I pick up a Volt-Ohm Reader. Does SeeMeCNC sell replacement parts like thermistors?

[Eaglezsoar]

Ok, so since I don't have a Volt-Ohm Reader at my disposal this moment I decided to switch the hot end and bed connector on the board and the same thing is happening where now the hot end is reading hot. So I can conclude the issue is between the wire and the Thermistor. I will have to dive deeper when I pick up a Volt-Ohm Reader. Does SeeMeCNC sell replacement parts like thermistors?

Yes, SeeMeCNC sells thermistors here: http://seemecnc.com/collections/parts-a ... r-100k-ntc

[teoman]

If you want to upgrade while you are at it, i would recommend watching:
http://www.youtube.com/watch?v=Fdb3nyu29ko

Makes life just a little bit easier.

[mpyr6]

So I have tested the resistance of the path from the plug itself and I get a rough reading of 84 at 200k ohms on the multimeter although the reading may not be accurate since I may have a bad multimeter. I have found that when left alone for an extended period of time the temperature drops back down to room temperature ~26 degrees celsius. I am uncertain if anyone else has had a similar issue. If it simply stated the max temp I would be led to believe that I simply need to replace the thermistor but since it's resistance is slowly degrading and that is increasing the temp readout I am currently at a loss as to whether or not there is some sort of interference that is building up a charge.

Showing the rate at which the temperature is increasing

http://youtu.be/5jcP8iPqTDY

Showing the soldering job

http://youtu.be/88_o0qxpch4

[Eaglezsoar]

So I have tested the resistance of the path from the plug itself and I get a rough reading of 84 at 200k ohms on the multimeter although the reading may not be accurate since I may have a bad multimeter. I have found that when left alone for an extended period of time the temperature drops back down to room temperature ~26 degrees celsius. I am uncertain if anyone else has had a similar issue. If it simply stated the max temp I would be led to believe that I simply need to replace the thermistor but since it's resistance is slowly degrading and that is increasing the temp readout I am currently at a loss as to whether or not there is some sort of interference that is building up a charge.

Showing the rate at which the temperature is increasing

http://youtu.be/5jcP8iPqTDY

Showing the soldering job

http://youtu.be/88_o0qxpch4

It sounds like the readings are unreliable. You need to get a new VOM, not an expensive one, you can get them for less than 20 dollars at many places.
You need reasonable accuracy when troubleshooting. The meters with a built in thermocouple meter are great and one such model is here:
http://www.amazon.com/Extech-MN35-Digit ... uple+meter

[mpyr6]

Problem solved! Turned out there was some sort of residue that was bridging the connection. I went through and cleaned up the solder joints and it's now reading perfectly! I am extremely happy I don't have to unsolder and re-solder the thermistor. Although now my PEEK fan isn't running during the print so time to problem solve that!

Thanks for everyones help and advice!

[Eaglezsoar]

Problem solved! Turned out there was some sort of residue that was bridging the connection. I went through and cleaned up the solder joints and it's now reading perfectly! I am extremely happy I don't have to unsolder and re-solder the thermistor. Although now my PEEK fan isn't running during the print so time to problem solve that!

Thanks for everyones help and advice!

I am glad that you solved the problem!
I still recommend the meter I gave you the link for.