So it looks like one of the PT100 amp boards on my dual titan build crapped out on me last night. Been running prints fine for weeks, then I ran some Nylon last night and started getting Thermal runaway errors mid print. Checking all the wiring this morning and when I go to fire back up I get persistent MAXTEMP error now and the board locks down in its safety mode. Continuity tested everything and made sure all was seated well, tried swapping wires and looking at the serial output and I can confirm that the error message changes from HEATER_0 to HEATER_1 when I do that so I'm fairly sure I've got a dead PT100 amp board now. I was figuring I could flash the firmware to a single extruder config for the time being while awaiting replacement parts but it doesn't look like I can even connect to the serial port to do this since the RUMBA is locked down for MAXTEMP. Any ideas how to temporarily disable the bad PT100 board?
You could connect a 105 ohm resistor to the PT100 connector. This should give you a reading of 24C on that extruder.