Not Printing at Set Temperature

[kas 0]

I am hoping to get some troubleshooting advice from the community about a problem with my UM not printing at the set temperature.

I have an Original UM with the UM heated bed upgrade, running the latest version of Cura on Windows 7, and connected to the computer via USB cable. The printer has been working well for over two years, until now!

The problem is: When I start a print, first the bed temperature rises to the set point (70C) and then the extruder temperature starts rising. The extruder temperature reaches the set point (218C) and keeps rising to MAXTEMP without the print starting. The work around is to cancel the print when the set point is reached, close the print dialog box, and start a new print; this time, as the extruder temperature falls to the set point the machine starts printing. This is problematic in several ways, including possible damage to the machine, extra time needed monitoring the printer, and causing the filament to melt further up (requiring a disassembly of the extruder to clear things up.)

Here's what I have tried so far:

- Made sure that the cooling fan cable is away from other cables

- Updated firmware (twice)

- Tried an earlier version of Cura

- Replaced the amplifier circuit board (twice)

- Replaced the cable from the amplifier circuit board to the main board

 

The problem still persists every time I print.

I'd appreciate any suggestion.