Panasonic KX-FT21RS - Manual (Page 65)

2.3.4.5. Power Supply Board Section
1. Key components for troubleshooting
Check the following parts first: F101, D101-D104, C106, Q101, PC101 and IC101.
This comes from our experience with experimental tests.
For example: power supply and lightning surge voltage test, with standing voltage test, intentional short circuit test, etc.
Caution:
If you find a melted fuse in the unit, do not turn on the power until you locate and repair the faulty parts (except for the fuse);
otherwise the fuse will melt again and you cannot pinpoint the faulty point.
In most cases, the symptom is that nothing is output. It is more likely that the fault is in the primary side rather than the
secondary side. Check the primary side first.
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