Panasonic KX-FT21BX Service Manual page 9

Broken parts repair details
(D101, D102, D103, D104)
Check for a short-circuit in terminal 4. If D101, D102, D103 and D104 are short-circuited, F101 will melt (open).
In this case, replace all of the parts (D101, D102, D103, D104, F101).
(Q101)
The worst case of Q101 is a short-circuit between the Drain and Gate because damage expands to the peripheral
circuit of Q101.
This is due to a very high voltage through the Gate circuit which is composed of R107, R109, D106 and IC101.
You should change all of the parts listed as follows.
F101, Q101, R107, R109, D106, IC101
(D201)
If D201 is broken, the oscillation circuit in the power supply cannot operate. Check it with an electric tester.
(Control circuit check)
Are R108, D108, R125
and D107 OK?
NO
Replace the broken part and IC101.
Power ON
24V output OK?
NO
Power OFF
NO
Are D201, IC201, PC101
and R222 OK?
YES
Replace the broken part.
Power ON
24V output OK?
NO
Power OFF
Replace the whole board.
(Model KX-FT21BX/KX-FT21BX-W)
KX-FT21BX/KX-FT21BX-W
YES
YES
A
YES
A
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