FWIW, here's the service manual:
http://www.repeater-builder.com/kenwood/pdfs/kenwood-th-f6a-and-th-f7e-svc-man.pdf
Reset procedures (which is in the manual)
PERFORMING FULL RESET
There are 2 ways to enter the reset mode selection.
However, the transceiver must be configured to the
Lock function OFF {page 38}.
When the transceiver is turned OFF:
1 Press [F]+ (POWER).
• All indicators are lit.
2 Release [F].
• Proceed to step 3 {below}.
From the Menu:
1 Press [MNU].
2 Turn the Tuning control or press [^ ]/ [dwn ] ARROW to select
Menu No. 31 (RESET?). Press [>] or [MNU].
3 Select the reset mode by turning the Tuning
control or press [^]/ [dn]. If you select “NO”, the
transceiver exits the reset mode.
4 Press [>] or [MNU] to proceed.
• If you press any keys, other than [LAMP] and
[MONI], the transceiver exits the reset mode.
• A reset confirmation message appears.
5 Press [>] or [MNU] to reset the transceiver.
• If you press any keys, other than [LAMP] and
[MONI], the transceiver exits the reset mode.