Kenwood NX-3720HG Service Manual page 160

Check the TX-RX UNIT PCB
Pass
Verify the BT/GPS control
signal (TXD2).
CN2 (15pin): Square
waveform UART data of 3.3V
logic.
Baud rate:
Default: 115.2kbps
After: 3.967Mbps.
Pass
Verify the BT/GPS control
signal (RXD2).
CN2 (14pin): Square
waveform UART data of 3.3V
logic.
Baud rate:
Default: 115.2kbps
After: 3.967Mbps.
Pass
[The MPU/DSP IC is
abnormal]
Replace the PCB.
Descriptions of signal names
1) 33BT: BT/GPS IC 3.3V power supply
2) 18BT: BT/GPS IC 1.8V power supply
3) 33GPS: BT/GPS IC 3.3V power supply
4) TXD2: BT/GPS serial data line connected to UART TX of MPU/DSP IC (MPU/DSP to BT/GPS IC)
5) RXD2: BT/GPS serial data line connected to UART RX of MPU/DSP IC (MPU/DSP to BT/GPS IC)
6) 18BT_HCI_RX: BT/GPS serial data line connected to UART RX of BT/GPS IC (MPU to BT/GPS IC)
7) 18BT_HCI_TX: BT/GPS serial data line connected to UART TX of GPS IC (BT/GPS IC to MPU)
8) /BT_SHUTDOWN: BT/GPS active control of MPU/DSP IC (MPU/DSP to BT/GPS IC) High
1-160 (No.RA054<Rev.001>)
Verify the BT/GPS control
Fail
signal
CP405 (3pin):
Square waveform UART data
of 3.3V logic.
[The RXD2 (18BT_HCI_TX)
line circuit is faulty]
Verify the CP405
Replace any abnormal parts.
Verify the BT/GPS control
Fail
signal (18BT_HCI_TX).
CP405, (4pin):
Square waveform UART data
of 1.8V logic.
[The RXD2 (18BT_HCI_TX)
line circuit is faulty]
Verify the CP405
Replace any abnormal parts.
Fail
Pass
Fail
Pass
Active, Low
[The MPU/DSP IC or
unchangeable part is
abnormal]
Replace the PCB.
[The MPU/DSP IC or
unchangeable part is
abnormal]
Replace the PCB.
Reset