Welcome to the SeeMeCNC Community

so just to start I did search for hot end issues but the data I've gathered doesn't match anyone elses issues so I'm asking for help.

Here is the situation: I did a print last night, took about 70 minutes, came out just find and looked good. It finished. I set the preheat settings to maintain the hotend and bed temps so I could print again right away. I noticed that the hotend temp was at 197 and change when it was supposed to be at 230. So I reset the printer connection and hit the preheat button and still only went to the 197 range.

I then went searching this forum and found similar issues involving miss-configured PID's so I went through the following steps:

1. let the hot end cool completely
2. set the preheat to 50 and the temp came up to 50 and held
3. set the preheat to 70 again it came up to temp
4. set the preheat to 100 again it came up to temp
5. set the preheat to 150 came up to temp but took it longer than I felt it should have
6. set the preheat to 170 as above came up just took longer than expected
7. set the preheat to 200 and only made about 193
8. set the preheat to 245 and temp made it to 210

So i thought this might be the PIDs, so I did a calibration and it came up to 200 as specified and adjusted the PIDs in the EPROM. Still getting the same results.

It feels like the hotend isn't getting enough power(I have nothing to back this up, just gut feeling). One observation that I did have is that when both the bed and hotend heaters are running the LED ring I have on the end effector usually has a faint pulse that coincides with one of the LEDs on the Rambo that blinks...that wasn't happening anymore. The LED on the Rambo was blinking, but not seeing the variation at the LED ring.

Any help would be greatly appreciated!!

Did you set the maximum output value to 255 in the firmware?

Check that the cables coming out of the rambo arent heating up too much (or the cables going in to the rambo for that matter).

It is completely normal that the speed of change of the hotend varies as it gets hotter. This is due to 2 factors.
1- As the heating element gets hotter, its internal resistance increases so you cannot push as much current (which generates heat) through it.
2- As the heating element heats up, the difference in temperature realtive to its surrounding is greater which implies that it will loose its heat much quicker. (that is why some people wrap it up in kapton tape or RTV)

After increasing the max pid value to the hotend, you can redo the PID but this time at 220 degs, or 230 degs. This should give you better pid values.

teoman wrote:Did you set the maximum output value to 255 in the firmware?

I haven't changed this since I built my printer months ago....why would it change all of a sudden?

I will check and make sure its set correctly, but again, why would it change?

There are 3 reasons why it could/would change.

1- the dangerous reason, as you push power through the cables the heat up and expand a little, and then when they cool they contract a little. Over a long period of time this has a wiggling effect and the cables become loose. Once they are loose they do not make such a good contact which in turn creates a point of resistance. So you are sending power out of your rambo, and some of that power if going to the hotend and some of the power is going to this new resistance in your system effectively heating it up.

2- Your resistors are getting old. As they age, their resistance goes up and they cannot suck as much power and provice less heat.

3- The rtv has dissapeared and now there is air/gas round the resistor, this is a form of insulation and the heat from the resistor cannot get to the metal of the hotend.


I had number 2 happen to me, and i swapped out for a heater cartridge which made a much tidier system.


If you have access to a multimeter then you can check the resistance of your hotend. That will give you an idea if it is the resistors.

Measured the resistance a few times and got readings from 7.5ohms to 8.3ohms. From what I've read this value is too high and probably means one or both of the resistors are failing.

I tried to do another calibration with the temp value to 230 and the max it got too was 210 and then it finally timed out. I still have to check the connections at the Rambo to make sure they are well seated, but its feeling more and more like the E3d v6 is going to get purchased and put on the printer sooner rather than later...

Heater cartridge install is very easy and does not cost much.

Ya I just order one and will have it on Saturday.

Thanks for the help Teoman!

Me ans several others have a thread regarding how to do it.

While you are at it replace the thermistor aswell. They sell a screw in type.

And you will be good to go untill you want to print with exotic filaments.