Extruder showing 79C while therm not plugged in

[DaGroundZero]

I flashed my Rambo with the Marlin firmware last night. I hooked up both my bed thermistor and my hotend thermistor. The hotend was reading 79C and the bed wasn't even registering.

powered down, unplugged the USB cable and switched the thermistor connections. I plugged in the hotbed to the top plug where the extruder was plugged in. I got the same 79C reading when I fired up Repetier Host.

I shut everything down, unplugged both thermistors, and booked up Repetier host. Still showing 79C with no thermistors plugged in.

I'm not sure if it was something that I did in the flash or what. I welcome any and all ideas.

Thanks,
Shawn

[mhackney]

What firmware were you using before and were temps working properly? Where did you get the Marlin firmware?

Speaking from experience if you blow the thermistor ports they register 0°, so 79 is very odd. I suspect a pins mapping error in the firmware. Did you choose the RAMBo board type?

[Polygonhell]

You an end up with odd temperature readings if the thermistor wiring is shorted with the heater wiring.

[DaGroundZero]

I was originally using the default firmware that came with the Rambo board. I'm using Marlin firmware that was referenced in the build instructions on page 81. I verified that the setup is for the Rambo board.

I've verified my wiring, and all looks correct. I checked for a short using my multi on both thermistors. Both checked out okay. I'm looking into an invalid pin mapping.

[Flateric]

I had the very same issue. IF it is still or not I bet Poly's diag. is correct. This is why I have a current thread running regardling externally controlling the hotend temp.

[DaGroundZero]

Could this short be in my Rambo? I've checked the wires, and all seems to be hooked up correctly.
I have been able to get the temp reading to change by change the value of the pull up resistor and upload the firmware without a therm plugged in.

If i wanted to use the two other thermistor ports for my hot end and bed, what would be the other pins on the Rambo?

I think this is the code in the pin.h that I would make the changes..

Code: Select all

#define TEMP_0_PIN         5 //6   // MUST USE ANALOG INPUT NUMBERING NOT DIGITAL OUTPUT NUMBERING!!!
#define TEMP_1_PIN         -1   // MUST USE ANALOG INPUT NUMBERING NOT DIGITAL OUTPUT NUMBERING!!!!!
#define TEMP_2_PIN         -1   // MUST USE ANALOG INPUT NUMBERING NOT DIGITAL OUTPUT NUMBERING!!!!!!
#define TEMP_BED_PIN       10

[mhackney]

You have a multimeter, so measure at the terminal connector unplugged from the RAMBo. It should measure about the same as the lone thermistor. Then, while continuing measuring, hold the hot end between your thumb and index finger with one as close to the thermistor as you can get. You should see the change in resistance at the multimeter. If not, then you have a wiring or thermistor problem. If that works, then you have a firmware or hardware problem. However, it does look like your pins are not correct, which leads me to question the firmware you grabbed. These come from the latest Marlin firmware for RAMBo:

Code: Select all

#define HEATER_BED_PIN 3
#define TEMP_BED_PIN 2 

#define HEATER_0_PIN  9
#define TEMP_0_PIN 0

#define HEATER_1_PIN 7
#define TEMP_1_PIN 1

#define HEATER_2_PIN -1
#define TEMP_2_PIN -1

[DaGroundZero]

I pulled the firmware from here https://github.com/johnoly99/Marlin-for ... kmax-rambo

Is this the correct place, or did I grab it from the wrong place?

I also checked both of my thermistors, and I'm not getting any resistance, but an open circuit. I measured the at the plug and the solder plugs of the onyx. Same thing for the hot end.

I did solder the wires onto the thermistor leads, would that have caused a problem?

I did make the changes to the firmware, and I'm still showing a temp when I start up Repetier host.

EDIT: Okay, I see what I've done to the pin output. I was looking under the section of the code for the wrong board type.. I finally went to the Rambo code section, and confirmed that my pins are setup like you have.
I was able to set TEMP_0_PIN to -1 and have the temp not register on the HOST.

I've ordered some new thermistors. I wonder if it is a combo of both bad ports on the Rambo and blown/wiring probs on the therms?

[mhackney]

I solder my thermistor leads too, no problems there. Did you check the thermistors disconnected or at the end of the wiring harness like I suggested? Normally they do not fail with no resistance (i.e short) they fail with infinite resistance. I still think you have a short, where did you measure the resistance? Those little thermistor leads take a little work to insulate from the hot end or Onyx central hole plating.

[DaGroundZero]

I checked at the end of the plug while it isn't plugged into the board. I also checked closer to the thermistor. I didn't check right at the thermistor wires, but about 6 inches back to the wires I soldered to the leads.

When checking with my multimeter, I just get a 1, I'm not seeing it change when I'm checking for a short.

I tried to measure the resistance at these points too. I'm not getting a reading at either point either. So, is this telling me that I have an open circuit, aka, I messed something up when wiring up everything?

Funny thing, my hotbed was measuring fine yesterday, but would quit registering once it went over 40c. once it cooled below that, it would register it again I took it apart, and re-soldered the therm to the pads on the bottom of the onyx.

[mhackney]

It really sounds like you have a short.

The Onyx thermistor hole has a copper trace around the perimeter. No one knows why, but it shorts the leads of the thermistor if it is not installed properly. I scraped the trace off, bent the thermistor leads to clear, and held in place with Ultra Copper. How did you install yours?

The hot end thermistor inserts into the hole in the aluminum. It is very easy for the leads to short out. There is a thin (<1mm) PTFE tube that you cut in half and slide over the thermistor leads. Even with that, you still have to make sure not to short.

Remove the thermistors and measure them. Sounds like you'll need to do that anyway if they are dead.

[DaGroundZero]

I did it about the same way aside for scraping off the trace on the onyx. I will start tearing it apart later tonight and measure everything as I go. Thanks for the help

[dbarrans]

Nobody knows why? I just figured the plated hole was there to supply power to the traces on the top of the Onyx, so I left the plating alone. My thermistor is embedded in RTV in the hole, with .012 ID PTFE tubing on its wires. Seems to insulate it just fine.

- dan

[DaGroundZero]

I've pulled my hot end apart. I have the thermistor out. I check the resistance across the leads, and I'm not getting anything. Can one blow a thermistor?

Also, are the thermistor pins on the Rambo board from pins 0-3?

I got shipping confirmation on my new parts, so I will carry on in a few days.

[geneb]

Yep. I literally blew mine in half when it accidentally shorted out against the hot-end wiring. This is the point where I learned, Thou Shalt Not Half-Ass Thy Insulation Job.

g.

[DaGroundZero]

I think I'm learning the same lesson, although, I thought I was doing a pretty good job. Time for round 2.. ha ha

[Flateric]

I've been following your thread here, I really hate to say this, but I strongly suspect you have blown your thermistor input pins on the Rambo. But hey you are in good company, a number of us here have done so.

Sucks.

This is why I am both exploring the possibility of using a seperate subsystem for my heated bed and hotend control. Also why I am trying to figure out how to re-map the thermistor pins to the analog ext just to the left of them. No sure thing that those are still ok either though. Seperate sub-system seems the most robust solution.

[DaGroundZero]

Flateric - I was thinking the same thing. It looks like I have one pin that seems to work, or at least register 0C when I don't have anything plugged into it. Once I get some new thermistors, I will give it another go.

I should have my new Rambo board and parts on Wednesday, so I will try to get it back together this weekend.

[Flateric]

Sorry dude, trust me I know how ya feel, my 3rd is on it's way. And I'm determined to make it the last I will need. It is just so scary easy to short the thermistors out on this giant aluminium bit o metal that we insist on heating right up past most insulations limits.

One thing I have found that would have prevent ALL of my shorts, simply because it comes pre-packaged in a ceramic cartridge is the ceramic cartridge heaters. Rather then the bare lead resistor heater setup.

The cartridges also come with 1/2 meter of very well insulated wiring so aside from the good insulation and the ceramic holding everything very firmly in place you also don't have a jumble of connectors right close in on the hot area and your tiny fragile thermistor.

[DaGroundZero]

Man. 3rd one. Dang. I don't like to hear that.

[DaGroundZero]

Okay. New hot end put on along with my new Rambo. All wired up and test out the hot end. I was able to extrude some ABS, so I'm happy so far. I've double checked my setup for my Onyx, and I've got another thermistor gooped in place. Saturday, I will add the hot bed and see if I can move into the configuration phase.

[Flateric]

I should note that all my lost Rambo's were during the use of the resistors as heating elements. I have zero problems with the cartridge setup.

So if you are still using the resistor based heating method make sure you triple extra check for possible shorts and potential shorts while in motion.

I like to zip tie the wires tight to the hot end platform so that any and all movement during use is limited to movement that cannot make it's way to the connections or anything on the plateform itself.

Good luck dude! I got my new Rambo yesterday and now I am trying to design a new all metal hotend V2.

[DaGroundZero]

Thanks for the info Flateric. I did just that. I also wrapped the connection points with a high temp silicone tape. I'm ordering a cartridge heater to upgrade too tho.

[JohnStack]

Today, my thermistor reads 371 C constantly - is this a blown thermistor?

Thinking I need to switch to magnetic arms....

[geneb]

That all depends on whether or not the machine is currently on fire.

g.