hi;
Firstly you see the mode switch pc board, you will need to clean clean and clean all the switches contacts with contact cleaner and eraser.
Then;
If you have an oscilloscope, you can probe Pin 15 just to make sure that signal is trying to go the right side head. The signal should be the same as Pin 16 to left side head.
Then you probe at J19 Pin 4 to make sure that signal arrives at the right side head safely.
Then;
99% sure it will record. In case not, the head is defective, change the head.
If you don't have a scope, you can use a audible signal tracer.
Hopes it help.