Thermistor 0 always reads 74 C.

[jbenuck]

Hi,

A homing mishap eventually led to my hot end thermistor getting damaged. I was not able to detect any connection between the leads using a multimeter. My replacement will arrive in a couple of days, but I have a problem that I need to resolve before it will do me much good.

M105 always reads about 74 C for the hot end temp regardless of whether anything is connected. I've even tried connecting my known good heated bed thermistor, but the reading is the same. Could I have fried something on the board? I have looked over the schematic, but nothing jumps out at me. I don't see a fuse in line with the thermistor connection. Any suggestions on how to determine why this is always reading something around 74 C?

One thing I've also considered is switching to the thermistor 1 connection, but the firmware doesn't have the pin set for that and what I see in the schematic for thermistor 0 doesn't match what I see set in the firmware so I'm at a loss as to what to put for the other two thermistor pin values. Does anyone have a recommendation for figuring out how the pins on the schematic map to what is used in the firmware?

Any help would be greatly appreciated.

Thanks!
-Joshua.

[Flateric]

Sigh, another possible casualty in the thermistor port passing on saga.

I hope not, but unfortunately I have seen it personally a number of times (3 myself) and a number with others too.

Here are a few link of others adventures and the ultimate conclusion of those adventures. Hope you may find some help in them.

It's happened to the best of us so you are in good company and not alone in it.

http://forum.seemecnc.com/viewtopic.php ... port#p8780

http://forum.seemecnc.com/viewtopic.php ... ort#p10196

http://forum.seemecnc.com/viewtopic.php?f=37&t=1520

[jbenuck]

Thanks for the quick reply! There's a lot of good info in those threads. Sad that I may have blown an input. I have a few ideas to try now. Thanks again!

[Flateric]

Ya, I went through 3 rambo cards, or rather 2 on my 3rd but if I blow this one I'm going for seperate independant control systems for each subsystem. Bed, hotend(s) and rambo all independant from each other and electrically isolated from each other. I already have the digital temp controllers all ready.

However I am not sure that day will come soon anymore after switching away from resistors for heating and now even cartridge based thermistors so shorting or damaging the wires causing a short is much more unlikely.

[jbenuck]

Would you be willing to provide links to the heating element and thermistors you are using? I really like the idea of reducing the possibility of shorting out those components.

[Flateric]

I do in those links, but I'll dig em up for ya in a bit here, in the middle of a project at the moment.

[Flateric]

Hey the seemecnc guys now offer them for $5.50.

http://shop.seemecnc.com/12V-40W-Heater ... -26601.htm

I'll dig the thermistor cartridge up for you still though.

[jbenuck]

I finally managed to make some progress here. The short of it is that two of my thermistor ports are shot, but I do have two that appear to still be functional.

Here's the process I went through for those that are interested.

First off, I'm using the Marlin for rambo firmware that was mentioned in geneb's manual. In Configuration_adv.h, I tried setting the number of extruders to 3. My hope was that M105 would then show me the readings on all four thermistor ports. It failed to do so. With that setting enabled, I still only see on hot end temp.

My second attempt was to try to change the pin assignments. In one of the above posts, someone else made the same mistake I did. I looked in pins.h and assumed the first set of pins was what was being used. I failed to recognized the ifdef surrounding it or that there are many sets of pin assignments in the file. That's what I get for using vim and less to view the file. (If you want to know why I wasn't viewing it within the arduino IDE, that is included below).

Once I identified that the rambo is motherboard 301, I was able to see that pins 0, 1, and 2 are the ones used for the thermistors. Mysteriously, the pin for the thermistor for heater 2 was not set. Changing my thermistor zero pin number from 0 to 1 gave me another constant reading. This time around 121.

Eventually, I set my heated bed thermistor pin to 1 and my hot end thermistor pin to 0. This resulted in a near constant reading for each regardless of whether a thermistor was connected. In short, the first two thermistor ports are shot.

Without the pin number for the remaining thermistor, I would have to chose between printing without a heated bed or being able to warm up the bed and not print. Neither is pleasant, though one is significantly more workable than the other.

At this point, I pulled up the schematic for the rambo again. The pins listed for THERM0, THERM1, and THERM2 all matched what was in the firmware. The one for the fourth was listed as pin 7, but the firmware listed that as belonging to heating element for heater 2.

Due to a vexing arduino on Linux problem that I'll describe later, I had pulled down polygon's firmware earlier in the day. Checking his code revealed that he had commented out the pin assignment for heater 2, but without revealing why in his commit comment. This was enough for me to decide to risk testing out my theory. I set that pin assignment to -1 and used pin 7 for my temp 0 pin and it worked!

I now can read temperature settings for two thermistors! Now I just need to wait for it to arrive tomorrow so I can rebuild my hotend.

What follows is a complete aside that explains why it took my so long to make any progress. Read it if you are interested in the travails of using a netbook running Ubuntu Linux to run a Rostock Max.

The netbook has a vertical resolution of 600. Using arduino 1.0.1, it is impossible to navigate to any file in a sketch that doesn't fit in the first page of the file dropdown. This is what led me to edit some files outside of the IDE. Upgrading to 1.5.2 fixes this issue. I cannot tell you how relieved I am about that!

At some point, I angered the arduino IDE and it refused to open the Marlin sketch. It would throw a NullPointerException. It took a while to even learn that because, I could not resize the console enough to read it. I eventually fixed that by editing preferences.txt to allow the editor area to be resized to something less than 500 pixels.

Googling for the NPE revealed that it was most likely a bug in the 1.7 JRE, but upgrading Java didn't fix it. It no longer threw an exception, but it also wouldn't open the sketch. This is what led me to download the other firmware in an attempt to see I could open other sketches.

This worked and it led me to an important realization. The exception was occurring within the recently used files chooser. I had to browse the directory structure to open the other sketch. Doing the same thing allowed me to open the Marlin sketch once again.

This is the second time that a recently used file list has tripped me up on the Linux builds of the tools for 3D printing. The first was within Repetier Host. It makes for a challenging experience. I'm just glad I've been able to find workarounds.

[jbenuck]

Flateric, I measured one of the holes for my heating resitstors in my hot end. It measure about 6mm so I think the ceramic heating element you found on the seemecnc website will fit. I guess the biggest change is that I'll need to run four wires instead of two to heat the hot end. Still, that's much better than a constant risk of shorting out something else on the board.

Thanks for the link!

[Flateric]

I'm sorry I didn't notice this until now, but you only need one heater cart for the hot end not two. So same wiring, just the two leads on one heater cart.