Panasonic KX-TD500 System Reference Manual page 1347

Testing sequence after dialing "90" is given below by using an example of PITS model
KX-T7130.
In LED test, " " means the light off, "
means flashing.
LED test
1) Testing the DN button indicators and the ICM button
indicator for lighting in green.
ICM button
2) Testing the DN button indicators and the ICM button
indicator for flashing in green.
ICM buttons
" means the light on, "
Panasonic
LED TEST
INTERCOM
1 2 3
ABC DEF
4 5 6
GHI JKL MNO
7 8 9
PRS TUV WXY
#
0
OPER
Panasonic
LED TEST
INTERCOM
1 2 3
ABC DEF
4 5 6
GHI JKL MNO
7 8 9
PRS TUV WXY
#
0
OPER
13-C-35
"
DN buttons
DN buttons