Hot end woes

I have just had a need to replace the thermister on my hotend. Before I even plugged in the hotend or thermister, I plugged the USB cable into the controller (ramps 1.4) and the display came on as it should. But it is displaying a temperature of 180 degrees for the hot end. The bed is displaying Zero. I have not even plugged in the thermister yet. After I plug in the thermister, it still reads about 180 degrees. So, to further complicate things, I can adjust the temp for the bed and it works, but I can not change the temp for the hot end, it remains at ZERO and gives a temp readout of 180 degrees. Everything else seems to work just fine. My hotend went bad and I replaced (done this before) and now it is not working. I disconnect the thermister from the Ramps board and it still is reading 180 degrees. It can not be the ramps board as it still reads bad with the ramps not even connected to it.

Milt
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You may have damaged the thermistor when you installed it, they are quite delicate.

I will try another thermister. Hopefully that is it. If i tell the hot end to go to a temperature above 180, the hot end will heat up.
Scary!!!

Milt

OK, I tried another thermistor. Even when there is no thermistor connected to the printer, it still reads 198 degrees. For some reason the ramps believes that the temp of the hotend is 198 degrees, even when the thermistor is not plugged in, and the power is cut to the hot end.

Further observations: I have disconnected all of the cabling going to the ramps board. The display still reads 199 degrees. Seems like it keeps going up? I disconnect the USB cable and plug it back in and it reads 199 degrees. I try to reset the display and it locks up. But would the display have anything to do with it, I think not. I just can not understand why it starts out at 199 degrees and not the room temp of 26 degrees (the bed temp display is reading 26). Keeping this open for a bit as I look at more STUFF!! I have now moved the hot end thermistor to the bed pins (T1) on the ramps board and it is showing that the thermistor is working. I moved the heated bed thermistor to the hot end pins (T0) on the ramps and it does not work. I then moved it to the third set of pins (T2) and neither one shows anything. I would imagine this is due to the fact that those two pins are not addressed in the arduino? How do I go about doing this so I can get this thing running? HELP!!!

Milt

Quote
mondo50m
Further observations: I have disconnected all of the cabling going to the ramps board. The display still reads 199 degrees. Seems like it keeps going up? I disconnect the USB cable and plug it back in and it reads 199 degrees. I try to reset the display and it locks up. But would the display have anything to do with it, I think not. I just can not understand why it starts out at 199 degrees and not the room temp of 26 degrees (the bed temp display is reading 26). Keeping this open for a bit as I look at more STUFF!! I have now moved the hot end thermistor to the bed pins (T1) on the ramps board and it is showing that the thermistor is working. I moved the heated bed thermistor to the hot end pins (T0) on the ramps and it does not work. I then moved it to the third set of pins (T2) and neither one shows anything. I would imagine this is due to the fact that those two pins are not addressed in the arduino? How do I go about doing this so I can get this thing running? HELP!!!

Milt

have you at any point shorted any of the thermistor inputs to heater wiring?

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Not that I am aware of. I just put in a different ramps card and get the same results as above. This pretty much narrows it down to the arduino or the firmware. Could I possibly need to reprogram the mega 2560? Although I do not know how that could have gone bad. This all happened because of a 64 year old brain fart. After cleaning the extruder and hot end, I plugged the thermister into the fan receptacle. So, the hot end heated up to the point of melting it. I bought the new hot end and thermister and have put it together. But all of the above has ensued. Yes, I am plugging everything in correctly this time (ha ha ha)! May reprogramming the mega help out? I have the firmware that came with the unit on my computer.

Milt

Bad Arduino Mega 2560. Replaced it with a spare and all is ok. Now I just have to flash the proper firmware. But, all is good.

Milt