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MK2a thermistor of heatbed resistance?

Posted: Tue Feb 16, 2016 2:37 pm
by Stunzasr20
HI
Just wondering if there should be any resistance between the 2 wires on the MK2a thermistor on the heatbed?
I tried testing but got no result.
I am thinking there should be resistance between these 2 wires.
I am wondering because I am not able to get a reading from my multimeter, and just switching the printer on and sitting there idling (not printing or moving etc) the LCD tells me that the heatbed is 46 degrees Celcius, which i highly doubt!

Attached is the screenshot to show basically what I mean,

Weirdly if I manually turn on the heatbed in Repitier Host, it appears the left side of the LCD (which I thought was the extruder temperature) slowly increases. The right side remains the same 45/95. The extruder does not get hot. The heatbed does get hot. The LED between the 2 heating wires on the heatbed illuminates yellow
Any suggestions appreciated.

Re: MK2a thermistor of heatbed resistance?

Posted: Tue Feb 16, 2016 4:14 pm
by Sherry
Stunzasr20 wrote:HI
Just wondering if there should be any resistance between the 2 wires on the MK2a thermistor on the heatbed?
I tried testing but got no result.
I am thinking there should be resistance between these 2 wires.
I am wondering because I am not able to get a reading from my multimeter, and just switching the printer on and sitting there idling (not printing or moving etc) the LCD tells me that the heatbed is 46 degrees Celcius, which i highly doubt!

Attached is the screenshot to show basically what I mean,

Weirdly if I manually turn on the heatbed in Repitier Host, it appears the left side of the LCD (which I thought was the extruder temperature) slowly increases. The right side remains the same 45/95. The extruder does not get hot. The heatbed does get hot. The LED between the 2 heating wires on the heatbed illuminates yellow
Any suggestions appreciated.
hi,
1.please tell me ther printer type and mother board.
2.according to you description, it is largerly because you connect thermistor cable of heat bed to extruder thermistor socket on motherboard. please if those cables connection are correct.
3.the MK2A resistance is 1-2ohms,make sure you meansure the resistance correctly.please refer to the post
http://www.geeetech.com/forum/viewtopic ... 19&t=17039
4.regarding to the problem "The right side remains the same 45/95".
please Checking if the T_HE1, T_HE2 and T_BED sockets on PCB are fine.
(1)Make sure you burnt correct geeetech firmware.
http://www.geeetech.com/forum/viewtopic ... 20&t=17046
(2)Make the T_HE1, T_HE2 and T_BED open circuit, short circuit and plug 100k thermistors on the three sockets. Checking if the corresponding temperature is normal. You can refer to the post
http://www.geeetech.com/forum/viewtopic ... 23&t=17030
1.png
1.png (51.53 KiB) Viewed 7024 times
The normal situation is as below while the hot ends and hot bed cool down.
QQ截图20160216161342.png
QQ截图20160216161342.png (5.46 KiB) Viewed 7024 times

Re: MK2a thermistor of heatbed resistance?

Posted: Tue Feb 16, 2016 6:00 pm
by Stunzasr20
Hi Eric
1. Geeetech Aluminum Prusa I3, with Sanguinololu board.
2. I retested and applied a little more force to the connection, attached should be the picture of what I was asking. I now have a reading and it is shown in both cases on the multimeter within each picture. Thermistor appears to be 4.53K ohms.
According to the Geeetech instructions/pictures of the printer on page 36, the wires for thermistor of heatbed are the thinner gauge wires and connect with a pre-fabricated clip (not the screw in items that are called heating wires for heatbed, as pictured within the instructions).

3.Heating wires for heatbed showed 1.8 Ohms, as per photo
4. Does that apply to my case, with Sanguinololu board. I cant see any similar labelling

Just a thought, could the polarity on either connection on the board matter?

Re: MK2a thermistor of heatbed resistance?

Posted: Tue Feb 16, 2016 8:25 pm
by Mark
It is the same method for your sanguinololu board, check if you have wrongly connected the thermistors.

Re: MK2a thermistor of heatbed resistance?

Posted: Thu Feb 18, 2016 8:31 am
by Stunzasr20
I am of the belief that it is correctly wired. Can you confirm the resistance of the thermistor for the headbed?

Re: MK2a thermistor of heatbed resistance?

Posted: Thu Feb 18, 2016 3:55 pm
by Mark
the resistance of the thermistor is about 100k at room temperature, and it will change according to the temperature, but you can measure the voltage between the pins of the thermistor connector, it should be 5V powered on with USB. And when you do the open circuit test for the thermistor connectors on the board, did you get 0 and 358?

Re: MK2a thermistor of heatbed resistance?

Posted: Thu Feb 18, 2016 7:21 pm
by Stunzasr20
The open circuit test showed me 0/0 0/45

Re: MK2a thermistor of heatbed resistance?

Posted: Thu Feb 18, 2016 8:24 pm
by Mark
well in this case the mainboard might be dead, BTW, are all the other functions of the printer working or not?

Re: MK2a thermistor of heatbed resistance?

Posted: Thu Feb 18, 2016 8:48 pm
by Stunzasr20
From what I understand other functions are working. For example I can load a stl. file and use rep host to generate the path (g code) and it runs pretty much how it should (that is after I remove in the Gcode editor the heating function section. So basically it does most things but extrude.

By mainboard are you referring to PSU or in my case Sanguinololu control board?

Re: MK2a thermistor of heatbed resistance?

Posted: Thu Feb 18, 2016 8:51 pm
by Mark
the sanguinololu board, not the PSU.