The L nozzle temperature in touch screen does not change when start heating L nozzle. In most cases, fuse for L nozzle heater, L heating cartridge, L interconnection board, main board & cables inside umbilical track can cause this issue.
a. Re-plug J10 & J39 in main board.
b. Start heating L nozzle in touch screen, check the LED – DS11 (upper left corner of main board), if it’s off, means the fuse of it was broken. Replace the fuse.
c. Unplug J39 in main board, use meter to check if there’s short of circuit via the 2 pins of J39. If yes, check the cables from L interconnection board to 2 L heating cartridges. If there is wear on the cable which makes conductor wire exposed. Replace heating cartridges as needed.
d. Replace L interconnection board. Replace main board. The figure below Error 311 is also a way to do troubleshooting on this issue.