Panasonic KX-FT21BX, Service Manual

Page: 85 / 206

TROUBLESHOOTING GUIDE
- 59 -
KX-FT21LA
cold soldering
LEADED PARTS
(section)
cold soldering
SMT PARTS
cold soldering
RESISTOR ARRAY
cold soldering
CHIP PARTS (section)
solder ball
SMT PARTS SMT PARTS
solder waste
3-7. Digital board section
One of most difficult problems to deal with is when the system will not boot up.
The symptom: No response when the power is turned on. (No LCD display, keys are not accepted.)
Then first thing to do is check the power source, If there is no problem with the power supply unit, then there is a problem with
the digital unit (main board).
As there are many potential causes in this case (ASIC, etc.), it may be difficult to specify what you should check first. If a mistake
is made in the order of checks, a normal part may be determined faulty, wasting both time and money.
Although the tendency is to regard the problem as a serious one (IC malfunction, etc.), usually most cases are caused by
solder faults (poor contact due to a tunnel in the solder, signal short circuit due to solder waste).
Note:
1. Electrical continuity may have existed at the factory check, but a faulty contact occurred as
a result of vibration, etc., during transport.
2. Solder waste remaining on the board may get caught under the IC during transport, causing a
short circuit.