Solved Bed Temp rises wildly after 15 min of constant temp.

I recently had to replace my RAMPS board on my Robo 3D R1 plus, because the bed heater wouldn't heat anymore. i found that the board was burned at the connector for the hot end.

After i got the new RAMPS board working and the firmware adjusted, i am noticing that when i send a print job to it, things look good for the first 15 minutes, then the bed temperature starts to either rise gradually or (depending on the slicer i use) shoot up suddenly ( i imagine it is as fast as the bed heater can heat.)

If i use a tool like octoprint, pronterface, or anything to send a g-code command to the bed heater, it will keep a constant temperature for at least an hour, with no rise in temp.

I have worked with the Firmware (marlin 1.1.9 bugfix v2) and i have set PIDTEMP values and also turned them off for testing. the only difference between the two was the behavior for the first 15 min. the PIDTEMP settings would keep the temperature more constant, while when it was disabled it would vary up and down by about 3 degrees (following the settings in the firmware).

i am really puzzled by this, does anyone have any ideas what may be up?

 

ok, i think i have found something. in the Configuration.h file there is a section where you define the motherboard

# define MOTHERBOARD BOARD_RAMPS_14_EFB
​

Everywhere i could find that mentions the locations of the Extruder, Fan, Bed shows this is correct for my setup.... except the original ROBO firmware...

in the original ROBO FW the motherboard is defined like this:

#define MOTHERBOARD 33​

Now i do have a new 1.4 motherboard so i couldn't put 33 in there but i did put the corresponding number for the BOARD_RAMPS_14_EFB which is 43. so my definition now looks like this in the Marlin 1.1.9 Bugfix v.2:

#define MOTHERBOARD 43 ​

after 2 dry runs and 2 runs with filament, I was not able to reproduce the issue of when the fan powering the fan increasing the bed temperature wildly. i am going to test some more, but i think this may be solved.