Kenwood TH-D74E Service Manual page 49

When a normal
condition is confirmed.
Check that the control signal
(/GPS_SHUTDOWN) of the
GPS is at 1.8 V. (Check with the GPS
turned ON.)
Side A: RA937 (pin 3 on the
lower right-hand side): 1.8 V
When a normal
condition is confirmed.
Check reference CLK: X930 of the
BT/GPS.
(Check with the GPS turned ON.)
Side B: Between C939 and C940:
Sine waves, 19.2 MHz, 0.2 to 1.2 Vp-p
When a normal
condition is confirmed.
Check the GPS control signal
(18GPS_RX).
Side A: RA932 (pin 3 on the lower
right-hand side)
Square wave UART data (1.8 V)
Baud rate: 115.2 kbps
When a normal
condition is confirmed.
Check the GPS control signal (RXD1).
Side A: RA931 (pin 1 on the lower
right-hand side)
Square wave UART data (3.3 V)
Baud rate: 115.2 kbps
When a normal
condition is confirmed.
Visually confirm the GPS RF input
circuit.
(SAW and GPS IC RF matching
circuit)
Side B: FL931 (SAW), L938, C968
and C970
When a normal
condition is confirmed.
Check the RTC circuit of the BT/GPS.
X931 (pin 3): Square wave,
32.768 kHz, 1.8 Vp-p
When a normal
condition is confirmed.
The BT/GPS (IC935) is defective.
Replace the control PCB.
Descriptions of signal names
(1) 33BT: BT/GPS IC 3.3V power supply
(2) 18BT: BT/GPS IC 1.8V power supply
(3) TXD1:BT/GPS serial data line (UART)(IC702(MAIN MPU) → IC930(LEVEL CONVERTER))
(4) RXD1:BT/GPS serial data line (UART)(IC930(LEVEL CONVERTER) → IC702(MAIN MPU))
(5) 18GPS_RX:Serial data line (UART)(IC930(LEVEL CONVERTER) → IC935(BT/GPS IC))
(6) 18GPS_TX:Serial data line (UART)(IC935(BT/GPS IC) → IC930(LEVEL CONVERTER))
(7) /GPS_SHUTDOWN:GPS active control (IC702(MAIN MPU) → IC935(BT/GPS IC)) High Active, Low Reset
When an abnormal
Replace the RA937. The MPU/DSP (IC702) is
condition is confirmed.
defective if the condition does not return to normal.
Replace the control.
When an abnormal Replace defective parts of the reference generation
condition is confirmed. circuit of BT/GPS as necessary.
Side A: Q930, R935, R936 and RA938
Side B: X930, C935, C939 and C940
Replace the RA930. If the condition does not return
When an abnormal
to normal, check the GPS control signal (TXD1).
condition is confirmed.
Side A: RA391 (pin 2 on the lower right-hand side):
Square wave UART data (3.3 V)
Baud rate: 115.2 kbps
The 18GPS_RX (TXD1) line is defective.
Side A: Be sure to replace the IC930, RA931,
and R930 as necessary.
When an abnormal
Replace the RA931. If the condition does not return
condition is confirmed.
to normal, check the GPS control signal (18GPS_TX).
Side A: RA930 (pin 4 on the lower right-hand side)
Square wave UART data (1.8 V)
Baud rate: 15.2 kbps
Check the GPS control signal (RXD1).
Side A: RA931 (pin 1 on the lower right-hand side)
Square wave UART data (3.3 V)
Baud rate: 115.2 kbps
When an abnormal
condition is confirmed.
When an abnormal
condition is confirmed.
When an abnormal
condition is confirmed.
When a normal
condition is confirmed.
When an abnormal
condition is confirmed.
When a normal
condition is confirmed.
When an abnormal
condition is confirmed.
When a normal
condition is confirmed.
Check the RTC circuit of the BT/GPS.
Replace the X931, L939 or C971 if any defects
are found in X931, L939 or C971.
The BT/GPS (IC935) is defective.
Replace the control PCB.
The MAIN MPU (IC702) is
defective.
Replace the control PCB.
The BT/GPS (IC935) is defective.
Replace the control PCB.
The GPS input circuit is defective.
Replace the corresponding parts as
necessary.
Change the control PCB with a new one
if individual parts cannot be replaced.
(No.RA044<Rev.001>)1-49