Panasonic KX-FC253UA-T / KX-FC258RU-T Service Manual ▷ View online
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12.5.4.15. An Abnormal Image is Printed
REFERENCE:
(*1): Test Mode (P.63)
(*2): Check Sheet for Signal Route (P.129)
(*2): Check Sheet for Signal Route (P.129)
(*3): How to Remove the Thermal Head (P.152)
(*4): We recommend making a copy of the test chart in Test Chart (P.210) and using it.
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12.5.5. Digital Board Section
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).
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 mal-
functions 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 sol-
dering 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.
functions 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 sol-
dering 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.)
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?
Please refer to Digital Block Diagram (P.123).
The ASIC (IC10) controls all the other digital ICs. When the power is turned on, the ASIC retrieves the operation code stored in
the FLASH ROM (IC16), 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).
The ASIC (IC10) controls all the other digital ICs. When the power is turned on, the ASIC retrieves the operation code stored in
the FLASH ROM (IC16), 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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12.5.5.1. 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.
remain normal. Other signal lines are not directly related to that failure even if they have faults or troubles.
As long as these signals remain normal, once the power is turned on, each IC can repeatedly output 3.3V (H) and 0V (L). The
following shows NG and normal wave patterns.
following shows NG and normal wave patterns.
NG Wave pattern
Note:
Refer to NG Example (P.128).
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Normal Wave Patterns
Remarks:
When you use an oscilloscope to judge whether a signal to be tested is normal or NG, perform the signal check in exactly the
same order as in [List 1]. (If the ASIC fails to access the FLASH ROM, the ASIC cannot access DRAM normally.)
The digital circuit actually operates according to the timing combinations of these signals. If the timing of these signals is even
slightly delayed, the circuit will not work. Nor will it if the IC is defective and the output voltage level is not normal although the
timing of these signals is accurate enough to meet the specifications. (Make sure that your oscilloscope is calibrated before
starting a test.)
Therefore, it is imperative to confirm whether each IC outputs the signal at the correct level. (See the I/O Pin No. Diagram.) The
signal level should be constantly output at between 3.3V (H) and 0V (L) as described earlier.
same order as in [List 1]. (If the ASIC fails to access the FLASH ROM, the ASIC cannot access DRAM normally.)
The digital circuit actually operates according to the timing combinations of these signals. If the timing of these signals is even
slightly delayed, the circuit will not work. Nor will it if the IC is defective and the output voltage level is not normal although the
timing of these signals is accurate enough to meet the specifications. (Make sure that your oscilloscope is calibrated before
starting a test.)
Therefore, it is imperative to confirm whether each IC outputs the signal at the correct level. (See the I/O Pin No. Diagram.) The
signal level should be constantly output at between 3.3V (H) and 0V (L) as described earlier.
Note:
Simply check the output level and make sure if the IC repeatedly outputs the signal at between 3.3V (H) and 0V (L).
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