Panasonic UF-5500 Service Manual page 187

2. Confirmation of the main unit
The unit can not communication with
PC through USB.
Is the voltage of pin1 of
CN300 about 5V ?
YES
Is the frequency of
X300 12 MHz ?
YES
In the state that
connected to PC with USB cable.
Is the signal waveform (1)-3 or
(2)-3 output from of pin2
or pin3 of CN300?
NO
Replace the IC 300.
NO
Make sure that PC and cable are
connected correctly.
NO
Check R384, C310,C311 and X300.
YES
Check the CN300 or USB cable.
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UF-5500 / 4500