I’ve been using the TAZ6 for over a year, so far, working wonderfully. But now the bed doesn’t heat, and troubleshooting is a real doozie. Neither LulzBot support staff nor I have been able to figure out what is going on.
Most recently, when I tried to print, the bed wouldn’t heat up, so the print wouldn’t begin because it was waiting for the bed to come up to temperature. When I lower the temperature manually, it will continue the print. Raising the temperature manually, or via a print job doesn’t work.
Things I’ve measured/tried:
- The display shows a reasonable temperature measurement (26C)
- The displayed temperature is responsive (can heat the thermistor and 26C increases as expected)
- Thermistor reads 95kOhms
- I think I can safely say the thermistor and its wiring are not the problem
- Reads 1.9 Ohms
- Seems appropriate
- Just to be sure, I replaced the bed assembly, no change
- I think I can safely say that the bed assembly isn’t the problem
- The F4 (15A automotive fuse) still has continuity
- The Mosfet seems to be in good shape
- The red blinky light is working, which I think is supposed to mean that the bed heater should be getting power
- HEATER WIRING
- I get 18-22V at the heater connector
- If I connect one side of the heater connector (don’t complete the circuit), I read 18-22V from the heater side of the connector to the open side of the connector coming from the RAMBo. This works on both sides. So I think the connections are ok.
- When I complete the connection and plug both heater connectors into the cable, the voltage drops to 10mV, practically 0.
- This makes me feel like the board is able to source the voltage, but wimps out as soon as there is any current draw. That makes me think it might be the Mosfet in some fugue state where it isn’t totally busted, but somehow is providing voltage, but gives up as soon as there is a current draw… But not sure.
Any thoughts on this mystery? Should I replace the Mosfet? With which one? Or do I need to plop down the $220 for a new RAMBo (or buy a new one cheaper somewhere else since I don’t need the connector kit - recommendations?)
Pictures that might help:
Blinky Heater LED:
[EDIT - SOLVED!!!]
Thank you so much for your help kmanley57 and piercet! I finally figured it out!
I replaced the RAMBo and after examining the old one, I found that the right pin for the heater wire was melted off of the RAMBo. Pretty scary/surprising stuff. It’s possible to fix, but just wanted to add this info for those of you looking for solutions at home.
Thank you for all of your help. Pictures below for the curious.
Note the long pin on the right of the long black connector - it is marginally melted off the board.
From the back you can see the solder has been melted on the leftmost solder pad in the line of through-hole connectors for the black connector. Crazy that those pins get that hot. Perhard the connection was just not quite good enough and heating up with all of that current passing through?