Hotend will not shut off!!!!!!!!!!!

[cjdavis618]

I have now gotten my 3rd rambo board because of gremlins.

Rambo 1 - Died due to cura slamming head down on parts after job finishes. (Thanks to the "Settings" addition in the file that can't be turned off) Melted leads into part and ruined the hotend.
Rambo 2 - Marathon print overheated board and thermistors shorted and board was unstable.
Rambo 3 - Seems to be working - But....

Now that I have finally gotten a weekend to rebuild and replace parts,
I added 2 new hotends using a dual extruder plate.
I got everything tuned up and uploaded the .91 firmware (Which is labeled for the Rostock max V1 that I have) but the settings are utter crap in it. Such as the Z steps per mm set to 2500 some odd steps( So please lord, don't disable your eeprom if you don't change that first). Steps per MM is off by about 18.4 steps (I'm now using the 20 tooth pulley, which is what discussions said the firmware set to 98.4 steps should be using fine). Measuring showed to be better at 80.750 and I hit my 1mm Z movement perfect based on my mitutoyo sub micron depth gauge. Anyway, now on to my latest and most frustrating problem.

I managed to run the autotune on the bed and it completed with no trouble.
I then tested the hotend 1 with (Firmware is not set for 2 hotends yet, Trying to crawl, then walk before I run again.) It turned on in Repetier and I got heat out of the right one. I then shut it off and let it cool. No problems.
I then decided to run the autotune on it and it went skyrocket high and wouldn't shut the hotend off. The command I used was m303 s200 like Gene's manual stated. Smoke started coming off the hotend and it got to 330C before I shut the power off. Rambo reads temp fine when I turned it on, but it also turns the hotend on when it is powered up. It appears it is doing this on both H0 and H1 now. It reads temp, but it will not shutoff. Hotbed is controlling normally. The firmware that used is the stock one from the Github link at Seemecnc and only changes were to steps per mm and the bed depth.



Any idea what happened and how I can get this fixed? I am sick of buying these rambo boards.

These are the new style hotends. They both read 3.8x ish ohms and appear to be working still. The thermistors appear to be reading ok as well. They match my Amprobe tmd-51 within 10C. I don't understand why the board is not shutting off the hotend. It is showing it has in repetier because the button is not lit for ext 1.

[Polygonhell]

You mention you have 2 hotends connected?
The firmware as it comes from SeeMeCNC needs significant modification to make 2 hotends work, and if you enable the second hotend without changing some of the settings, it will continue to heat until it melts itself becasue it's not by default using the correct thermistor pin.

If you have the second hotend heater connected to heat2 on the Rambo you will have the same issue, the pin for it is mapped in the firmware as a PEEK fan, so when it triggers it will just continue to heat. My guess is that this is what you are seeing, you tried to run M303 on hotend 1 and it caused hotend 2 to just heart continually.

The steps per mm on a 20 tooth pulley with 16x uStepping should be exactly 80, it's simple math, 3200 steps/revolution divided by 40 (20 x 2mm per belt tooth). The older 15 tooth pulleys were 53.333 (on the original 8x uStepping) or 106.666 for the newer Rambos.

Now assuming you didn't set the firmware to 2 extruders and assuming you have the one hotends heater and thermisor correctly connected, and the other disconnected, you can look at the lights on the board under the connections to see what is turned on and when

If you are changing firmware I'd strongly recommend you get back to one working extruder and hotend first, the changes to get 2 extruders working aren't trivial, your best bet would be to find someone with a similar configuration and have them give you copies of pins.h and configuration.h.

[cjdavis618]

Thanks Polygonhell,

I have disconnected the second extruder, hotend and thermistor for now until I can get further into this.

That would make sense about the peek fan, because I had it on to cool the hotend down after the overshoot.

I do have a fan on both the board and the hotends to cool from the same output. I keep them on all the time since I print in ABS only.

I just tore everything back down to double check and re-label all the cables to make sure nothing got crossed and it tests out good.

Both Thermistors read 70kohms on the hotends,
Both Resistor sets read at 3.55ohms after setting idle while making the post.

Board is running fine. I can disconnect my laptop usb and it will turn on and rest idle. So I will try again and report back. Thanks for the help.

[cjdavis618]

Poly, I just wanted to update and say that this was the case. Disconnecting the second hotend did the trick. So it looks like the default firmware is like yours and it powers the hotend from the fan pin.

I'm trying to catch up on the forums after the hiatus and parsing the new developments so I can proceed after calibration.

Thanks again for the help.