Hytera MD78X, Service Manual, Page: 252 / 519

Troubleshooting Flow Chart
UHF3 (350
–
400 MHz)
34
Check RX circuit
Q920 outputs 9V3A?
Check the power-on
circuit
No
Q902 outputs 9V1A?
Yes
Check Q902 and
Q903
No
Front panel output is
normal? [1]
Yes
Replace the front
panel
No
Input an IF signal (73.35
MHz) and test whether the
circuit is normal?[2]
Yes
Second LO is normal?
[3]
No
Check Q701 and
peripheral
components
No
TP707 receives a
18 MHz signal?
Check D702 and
relevant
components
Yes
No
TP6101 output is
normal?[4]
Yes
TP6106 output is
normal?[5]
Yes
No
Check RX VCO and
LO amplifier
No
Check D6106, T6100,
T6101, and peripheral
circuits
Sensitivity at TP6104 is
normal?[6]
Yes
Yes
Check Q6102, D6103,
D6104, and peripheral
circuits
Check L809, L813,
M801, and peripheral
circuits
Yes
No
End
Sensitivity at TP6103 is
normal?[7]
Check Q6100, D6101,
D6102, and peripheral
circuits
No
Yes
Description of normal situations:
[1] During sensitivity test, use a communication test set to demodulate the audio signal at TP4012 and
TP4016. If the signal is demodulated normally, it is concluded that the front panel is defective.
[2] Use the communication test set to apply a 73.35 MHz IF signal at the mixer, and sensitivity is about
-110 dBm.
[3] There is a second LO signal (71.1MHz) at TP704.