Err: MINTEMP - seems like a grounding problem

[runamok 0]

Hi,

I just recently got an Ultimaker Original.

I'm getting an Err: MINTEMP error reported on the display.

The temperature reading is either a very low number (less than 10) or 0.

It tends to fluctuate a little around 6-8..

It seems to be some sort of grounding problem between the thermocouple and the heating element.

If I remove either one from the hot block, the temperature becomes stable at 20deg.

I have a dual extruder kit, and I've swapped the TC, the heating element and the TC amplifier board and got the same results.

I've checked all the connections (a few times) and it all looks good.

I've got the latest 15.02 firmware from Cura.

Another odd behavior is that when I put my hand anywhere near the TC wires (or for that matter, anywhere near the top of the printer) the temperature reads around 20..

If I touch the bottom of the printer (on the wood), the temp goes to 0.

Any tips would be great!

Thanks!

 

[runamok 0]

A bit more information..

I saw a comment from 'gr5' suggesting that the TC wire was very sensitive to other wires nearby

(http://umforum.ultimaker.com/index.php?/topic/4680-ultimaker-original-not-working/?p=40437)

So I routed the TC wires as far away from the fan and heater wires as I could

This showed some improvement.. When I turned the power on, it now hovers around 15-18 degrees..

Enough where it won't immediately throw a MINTEMP error.

BUT, if I touch the printer in any way (including the control knob on the ulticontroller) the temperature immediately drops to 0 and throws the MINTEMP error.

As I was searching around for the reference to that post, I found another post about connecting the ground wire of the fan to the printhead..

http://umforum.ultimaker.com/index.php?/topic/4355-grounding-the-print-head-for-better-temperature-stability/

I'm not at home currently, but that sounds very promising.

Clearly the print-head is floating around at some odd potential, and the wooden case doesn't provide much of a ground path..

I will try that tonight...

Thx

 

[gr5 2,173]

Your grounding issue theory is sounding promising. How about using a volt meter to test the ground?

 

[gr5 2,173]

The wires that are most likely to break (90% of the time) are just above the head. There is a 3 wire connector there that connects to the board and it is supposed to go through an F shaped strain relief. Also the connector is supposed to be crimped but some people at UM got the idea to solder it instead which is a problem - the solder wicks into the wire under the insulation and causes the wire to be more stiff and more brittle. So after a year or so the wires often break - inside the insulation where you can't see it. Fortunately there is a spare wire bundle for the second nozzle which I assume you don't have. So you can swap to that wire (on both ends - you have to swap underneath the UM also).

 

[runamok 0]

Yep, I've tried swapping the two TC cables and had similar results..

They look crimped, and I checked the black-red-yellow cable with an ohm meter, and it seemed to have continuity on all 3 wires..

I checked potentials with my voltmeter relative to the USB plug case, and everything seemed nominal (0.02v or less)

I tried a variety of spots on the print-head, the axes, etc..

I tried connecting the fan ground (black) to the printhead screws and that put the temperature at 383, which seemed a little high.. so I disconnected that..

I also tried reflowing a few of the connectors on the board (the TC, the heater, the fan) with my soldering iron.

Didn't seem to change anything..

Are there any troubleshooting guides that can lead me through what voltages should be where, resistances, etc?

Thanks

 

[runamok 0]

The fan appears to be the culprit. If I disconnect it now, everything behaves nicely.

The TC triple wire was crimped, but the fan cable appears to be something else.. it has shrink tube on the connections.

I'm going to see if I can rework those.

Thanks

 

[gr5 2,173]

Keep the fan cabling far from the section of wiring that runs from the tiny board on the head down to the nozzle. "far" means like an inch. The EMI (electromagnetic interference) from those wires can mess up the temp reading.

Usually this is only a problem in PWM mode but when the fan is at 0% or 100% it shouldn't cause much EMI.

Alternatively the current going to the (either + side or ground side) fan could cause a voltage drop somewhere on the PCB or in the wiring to the fan. Do you have schematics for the PCB? They are freely available but you have to know where to look.

 

[runamok 0]

Thanks for the tips.

I don't have the schematics, that would be a great reference if you can post a link..

Thanks!