Panasonic KX-FHD332C Service Manual page 130

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 FLASH 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
resoldering it, in many cases the problem will be resolved.
An explanation of the main signals (for booting up the unit) is presented below.
Don't replace ICs or stop repairing until checking the signal lines.
An IC malfunction rarely occurs. (By understanding the necessary signals for booting up the
unit, the "Not Boot up" display is not a serious problem.)
What are the main signals for booting up the unit?
The ASIC (IC501) controls all the other digital ICs. When the power is turned on, the ASIC
retrieves the operation code stored in the FLASH ROM (IC523), then follows the instructions for
controlling each IC. All ICs have some inner registers that are assigned to a certain address.
It is the address bus by which the ASIC designates the location inside each IC. And the data bus
reads or writes the data in order to transmit the instructions from the ASIC to the ICs.
These signal lines are all controlled by voltages of 3.3V (H) or 0V (L).
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