Panasonic KX-FM89BX, Service Manual

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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.
What are the main signals for booting up the unit?
Please refer to
DIGITAL BLOCK DIAGRAM ().
The ASIC (IC501) controls all the other digital ICs. When the power is turned on, the ASIC
retrieves the operation code stored in the ROM (IC502), 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 5V (H) or 0V (L).
2.3.6.1. DIGITAL BLOCK DIAGRAM
You also need to check the signal lines listed here [List 1] when the unit fails to boot up the
system. Those signal lines should remain normal. Other signal lines are not directly related to
that failure even if they have faults or troubles.
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