Resistance issues

I'm just about ready to wire up my machine but I came across some issues whilst checking the resistance. The thermistor in the hot end is giving me ~140Kohm while the thermistor in the bed is giving ~100Kohm(as it should), both at room temp. Can anyone explain?
Secondly the bed heater is giving me 1.4Ohm when in the manual it says it should be 1.2 - will this be a problem?
And also, I've noticed one of my limit switches dosn't seem to be doing anything when I press the button(it dosn't make a click sound). I not really sure what the function of the limit switches are but I presume they are a precautionary measure to prevent damage to the machine if the calibration is off or something? Do I need a new limit switch?
Any help is greatly appreciated.
Thanks

Edited 1 time(s). Last edit at 12/23/2013 02:25PM by tforde90.

RE the limit switches

not just to prevent damage. when you turn it on, before starting the print, it will home, the motors will run to the end, untill they touch the swich. that's how they knw where 0 is.
are you sure it is doing nothing, check with the ohmeter .
sometimes you may not hear the click. get a voltmeter, and check resistence between legs when the switch is pressed or not. (should be 0 resitence in one case and a break in the circuit in the other)
or check it in software - page 67 of the manual
(or just wire a 9v battery and use your tounge like we did before DVMs)

Edited 2 time(s). Last edit at 12/23/2013 02:50PM by avishalom@gmail.com.

Yes the meter is reading 0.4 and no change when I press the switch. Also on my other 2 limit switches I'm getting no reading (open circuit) and also no change when I press the switch.

I have never had a report of a faulty switch so if you have three it seems very odd. Are you testing between the outer two contacts and not connected to the Melzi?

Two ways I can think of damaging them: one is over tighten the screws (but I would expect that to break the printed part first) the other would be overheat them while soldering so the casing melts and the contacts move. Do the solder tags look like they have moved?

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[www.hydraraptor.blogspot.com]

Switch problem solved I had soldered to the wrong pins.
The thermistor problem fixed itself I'm now getting ~100kohm for both.
I'm still getting 1.4ohm instead of 1.2 for the bed heater tho. Will this be a problem?

How did you fix the switch that did not click?

Have you subtracted the resistance of your meter leads from the bed resistance?

I don't think 1.4R will be a problem as the wires always add a little to the actual resistance of the bed so it tends to measure a bit more at the Melzi end.

Edited 1 time(s). Last edit at 01/03/2014 02:13PM by nophead.

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[www.hydraraptor.blogspot.com]

Why does this topic have 23,000 views?

I don't know. Perhaps it matches a common Google search for something completely different or somebody has put a link to it on a popular site.

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[www.hydraraptor.blogspot.com]

The switch still doesn't click but it is functioning properly when it is pressed in

Discovered another issue from testing the switches in pronterface.
M119 gives the result:
"x_min:L y_min:L z_max:L"

Why is it z_max instead of z_min?

Because the Z limit switch is defined in firmware as the maximum value of Z not the minimum.

Edited 1 time(s). Last edit at 01/14/2014 02:24PM by neildarlow.

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I try to write with consideration for all nationalities. Please let me know if something is unclear.
Printing with Mendel90 from fedora 25 using Cura, FreeCAD, MeshLab, OpenSCAD, Skeinforge and Slic3r tools.

Is this a problem or is it as it should be? According to the manual it should say z_min:L

Yes the manual is wrong. It should be z_max:L.

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[www.hydraraptor.blogspot.com]