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