XIEGU
Product Maintenance Manual G90/G90S Portable Short-Wave Transceiver
XIEGU All Rights Reserved Version No.: 1.0 2022-07 Page
44
of
48
Fault phenomenon: when switching frequency range, LPF relay does not act
Maintenance methods:
1. The relay of each LPF frequency range is controlled by the control
chip ULN2803 output .
2. Voltage of output control pin corresponding to ULN2803:
Pin voltage
corresponding to
each band output
of ULN2803
Selected Voltage
Unselected
Voltage
0.7V
13.8V
3. According to the circuit schematic diagram, measure the band
voltage of the output pin respectively, to judge whether ULN2803
works normally.
4. Check whether the previous stage control chip 74HC595 of
ULN2803 has poor welding.
Frequency range control
chip
