Panasonic KX-FLM551 Service Manual page 91

When the unit fails to boot up the system, take the troubleshooting procedures very carefully. It
may have a serious problem.
The symptom: No response when the power is turned on. (No LCD display, and keys are not
accepted.)
The first step is to check the power source. If there is no problem with the power supply unit,
the problem may lie in the digital unit (main board).
As there are many potential causes in this case (ASIC, DRAM, 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.
Before we begin mass production, several hundred trial units are produced at the plant, various
tests are applied and any malfunctions are analyzed. (In past experiences, digital IC (especially,
DRAM and ROM) malfunctions are extremely rare after installation in the product.)
This may be repaired by replacing the IC, (DRAM etc.). However, the real cause may not have
been an IC malfunction but a soldering fault instead.
Soldering faults difficult to detect with the naked eye are common, particularly for ASIC and RA
(Resistor Array). But if you have an oscilloscope, you can easily determine the problem site or
IC malfunction by checking the main signal lines.
Even if you don't have such a measuring instrument, by checking each main signal line and
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