Lulzbot Taz 4: Hotend heats but doesn't stop when reaching set temp but reads temp

Hello all!

I have been printing with my Lulzbot for a couple of years without issue; recently the lulzbot has started to go into a “thermal” runaway.

I have tried swapping out to a secondary hotend to no avail; what happens is I set a temp on the screen and the hotend just keeps going without stopping and then kicks the error.

I have not updated the firmware or made any other changes; to the unit. I can purchase another hotend but I wanted to be sure it was hardware prior to purchase.

The hotend IS heating up and the temp IS correct; it just doesn;t stop. Thank you for any feedback or help.

I have flashed new firmware to the device; it seems like it has something to do with the actual hotend temp sensor.

I have ordered the LulzBot M175 Single Extruder Tool Head (arriving by 9/9) and have flashed the device with stock Marlin. I am planning on upgrading my fleet of printers to the Lulzbot KT-PR0051NA TAZ Workhorse down the road this year so the hotend “seems” to make the most sense.

The device (minus the temp issue) seems to respond correctly even with gcode. The bootloader was royal messed up and took me a while while flashing the firmware the first time (shug).

Hotend: LulzBot M175 Single Extruder Tool Head - 1.75mm x 0.50mm | MatterHackers

The hot end temp sensor, a thermistor, does not actually control the heater in the hot end. It just reports the temperature back to the controller board, and it is up to the controller board to decide when the temperature has reached the desired point and cut power to the heater cartridge.

So it is very puzzling that you can have a system that reads the temperature correctly and heats, but doesn’t stop when it reaches the set temperature. I don’t have a answer for how that can happen, but it is very likely that a new tool head will not fix the problem as the power to the heater is controlled by the control board.

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@cdsmith That’s what I was assuming; I figured the flashing of the firmware would kick the issue but it didn’t.

I am wondering if there is a short in the board somewhere that is causing this; I’ll order a new board as well.

(edit-1) Looks like I may be just upgrading to the Archim2 at this point; same price as the Rambo 1.4 but more features. (shrug)

*What’s the best procedure for replacing the Rambo board?
*32-bit ARM based controller??

If there was a short in the board I would think that the mostly likely behavior would be that it would just start heating the hot end as soon as you turn the power on. It’s a bit odd if it waits for you to turn on the heat and then sticks on. But I suppose that it is possible that the board could have a fault that could make it behave this way.

I don’t know much about what’s different with the Taz 4 but upgrading to an Archim2 would likely require changes to the connectors and wiring to get everything to plug into the board, and probably a new custom firmware as well. Maybe someone has done this already and documented the process online somewhere.

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From the research I have done; it looks like the connectors are the same; I am assuming the firmware will take some tweaking but hopefully not too much (excluding the wiring to the print head).