Panasonic KX-TCD420GS Service Manual page 53

The movement of Battery Low indicator is wrong.
The handset does not respond to a call from base unit.
The handset does not transmit or the transmit frequency is off.
The transmit frequency is off.
The transmit power output is low, and the operating distance between
base unit and handset is less than normal.
The reception sensitivity of base unit is low with noise.
Does not link between base unit and handset.
The reception level is high or low.
The transmit level is high or low.
* : Refer to Adjustment
15.1. Adjustment
Please follow the items below when BBIC or EEPROM are replaced.
Items
Adjustment
(A) 4.0V Supply
Confirmation
Symptom
()
Point
1. Confirm that the consumption current is < 200mA , that is, there is no short circuit.
-
2. Confirm that the voltage between TP14 and GND is 4.1V ± 0.2V.
Procedure*
49
Remedy
Make confirmation in item (A)~(C
(F)~(G)
Make adjustments in item (A)~(C
(H), (J)~(N)
Make adjustments in item (A)~(C
(H)~(K), (M)
Make confirmation in item (A)~(C
(H)~(K), (M)
Make confirmation in item (I), (L)
Make confirmation in item (L)
Make confirmation in item (A)~(C
(H)~(N)
Make adjustments in item (O)
Make adjustments in item (P)
Check
Replac
Parts
IC1,F1,R
R4,C33
D1,C15
C14,Q1
R2,D2,R
C26,X1,C
C17