Panasonic KX-FT63BX Service Manual page 61

After the power is turned on, the ASIC (CPU) initializes and checks each IC.
The ROM, SRAM, and Modem are checked.
If initialization fails for the ICs, the system will not boot up.
CROSS REFERENCE:
NG EXAMPLE (P.63)
CHECK THE STATUS OF THE DIGITAL BOARD (P.64)
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KX-FT63BX / KX-FT63BX-W