Codan NGT 2010 RF Technical & Service Manual page 674

NRI—Fault finding
Testing the NRI Microcontroller PCB
Drawing
A number of test points are provided on the NRI Microcontroller PCB to enable
measurements to be made that assist in fault finding. A multimeter and an oscilloscope
(if available) may be used to measure the signals at each of these test points.
shows the expected signals at the test points. If these signals fail to meet specification,
Table 8
that each test point be measured in the order that they appear in
Table 8: Test points on the NRI Microcontroller PCB
Test point Description
+5 V Regulated +5 V
supply rail
+10 V Regulated +10 V
supply rail
16 MHz Clk Microprocessor clock
signal
RESET Active-high system
reset signal
+5 VQ Regulated +5 V quiet
supply
RX_AF1 CIB receive audio
path 1
TX_AF CIB transmit audio
path
AUD– CIB system
audio –
280
08-05854 (sheet 1)
provides the possible causes of the fault and the action required. It is important
Acceptable
signal/level
+5.0 V ±0.1 V
+10.0 V ±0.1 V
16 MHz ±100 Hz
5 V p–p square wave
Logic-low just after
system power supply
connected
+5.0 V ±0.1 V
+5.0 V ±0.1 V with
no audio present
+5.0 V ±0.1 V with
no audio present
+5 V with ∼ 6 µs wide
5 V p–p low-going
pulses every 80 µs
Table
Possible fault causes Action
No power input
Failed switchmode
controller
Failed
microcontroller, RAM
or ROM chip
Failed regulator
Failed analog
component(s)
Failed microcontroller Replace PCB
Failed microcontroller Replace PCB
Corrupted program
code
Failed analog
component(s)
Failed analog
component(s)
Failed analog
component(s)
Failed Vocoder PCB
Failed programmable
logic device
Failed analog
component(s)
Firmware failure
NGT Transceiver System Technical Service Manual
Table 8
8.
Check for +12 V
across C139
Replace PCB
Replace PCB
Replace PCB
Replace PCB
Replace PCB
Replace PCB
Replace PCB
Replace PCB
See Table 9
Replace PCB
Replace PCB
Attempt to
reprogram if
possible