Motorola Radius Cm200 Cm300 Pm400 Detailed 6881098c00 A Manual

Receive Audio Circuits2-19
9.0 Receive Audio Circuits
Figure 2-9 Receive Audio Paths
9.1 Squelch Detect
The radio’s RF circuits are constantly producing an output at the discriminator (IF IC). This signal 
(DISC AUDIO) is routed to the ASFIC CMP’s squelch detect circuitry input DISC (U504-pin 2). All of 
the squelch detect circuitry is contained within the ASFIC CMP. Therefore from a user’s point of 
view, DISC AUDIO enters the ASFIC CMP, and the ASFIC CMP produces two CMOS logic outputs 
based on the...

2-20THEORY OF OPERATION
9.2 Audio Processing and Digital Volume Control
The receiver audio signal (DISC AUDIO) enters the controller section from the IF IC where it is.DC 
coupled to ASFIC CMP via the DISC input U504-pin 2. The signal is then applied to both the audio 
and the PL/DPL paths
The audio path has a programmable amplifier, whose setting is based on the channel bandwidth 
being received, an LPF filter to remove any frequency components above 3000 Hz, and a HPF to 
strip off any sub-audible data...

Receive Signalling Circuits2-21
9.4 Handset Audio
Certain handheld accessories have a speaker within them which require a different voltage level 
than that provided by U502. For these devices HANDSET AUDIO is available at control head 
connector J2 pin18.
The received audio from the output of the ASFIC CMP’s digital volume attenuator is routed to U505 
pin 2 where it is amplified. This signal is routed from the output of the op-amp U505 to J2-pin 18. 
From the control head, the signal is sent directly...

2-22THEORY OF OPERATION
The low speed limited data output (PL, DPL, and trunking LS) appears at U504-pin18, where it 
connects to the µP U403-pin 80.
The low speed data is read by the µP at twice the frequency of the sampling waveform; a latch 
configuration in the ASFIC CMP stores one bit every clock cycle. The external capacitors C5028, 
and C5026 set the low frequency pole for a zero crossings detector in the limiters for PL and HS 
data. The hysteresis of these limiters is programmed based on the...

Chapter 3
TROUBLESHOOTING CHARTS
This section contains detailed troubleshooting flowcharts. These charts should be used as a guide in 
determining the problem areas. They are not a substitute for knowledge of circuit operation and 
astute troubleshooting techniques. It is advisable to refer to the related detailed circuit descriptions 
in the theory of operation sections prior to troubleshooting a radio.
Most troubleshooting charts end up by pointing to an IC to replace. It is not always noted, but it is...

3-2TROUBLESHOOTING CHARTS
1.0 Troubleshooting Flow Chart for Receiver RF (Sheet 1 of 2)
Problem in 12 KHz and 
25 KHz channel spacing
9V on
R310 (LNA)
OK
?Check
RX_ENNoGo to 
DC Section
Ye s
RX_EN
ON ?NoSW ProblemYe s
START
LOC_DIST
ON
?SW Problem
LO
POWER
OK ?
Go to SYN 
Section
Ye s
Ye s No
No
Go
to A
Ye s
3 V
to U301
Okay ?No
Check
LOC_DIST
Go to
DC Section
Ye s
Check D301-304
Replace IF Filters( FL304, FL301
If problem in 25 KHz spacing
Check
TPI
Check 5V
on R337 (UHF),
R336 (VHF)
5V
(IF AMP)
OK ?Go...

Troubleshooting Flow Chart for Receiver RF (Sheet 1 of 2) 3-3
1.1Troubleshooting Flow Chart for Receiver (Sheet 2 of 2)
3V
(IFIC -Vcc)
OK ?
Installation
OK ?
Ye s
Ye s No
No
A From
Check visually
FE and BE
components
installation ?
Inject - 40dBm (CW)
to RF connector
Check Power on
C335 (UHF) C332 (VHF)
RF
Power
> -28 dBM
?Ye s NoCheck Power on
C337 (UHF),
C336 (VHF)
Go to 
DC Section
Check 
the component
FE Problem
Replace 
Q303, Q301
Check passive
componentsRF
Power
> -28 dBM
?Ye s
NoReplace 
Q305,...

3-4TROUBLESHOOTING CHARTS
2.0 Troubleshooting Flow TX RF (No Output Power)
START
Key the radio using
Radster (type k)
NoYe s
Ye sNoTune the
PA_BIAS
Press F6 and
read the ASFIC byte
Is
Byte
#04=0
?Put 80 Hex in byte #06
and measure the
Output Power
Is
POUT
< 1 Watt
?Replace
L108
End 

Troubleshooting Flow TX RF (No Output Power) 3-5
2.1Troubleshooting Flow TX RF (No Output Power/No Current)
START
Key the radio using
Radster (type k)
NoYe s
Ye sNoTune the
PA_BIASMeasure the
resistance from
R131 to groundIs 
POUT >
10 Watts
Put 80 Hex in byte #06
and measure the
Output Power
Is
20kOhms
< R 

3-6TROUBLESHOOTING CHARTS
2.2Troubleshooting Flow TX RF (Not Txing at Nominal power)
Press F6 and read the ASFIC byte
Is byte
#04=0
?
No
Tune the PA_BIAS
Ye s
START
Key the radio using radster (type k)
Ye s
Measure the resistance 
from R131 to ground
Is R131
< 1K Ohm
?
No
Repalace PA (Q100)Tune the K and M factors 
using the Tuner tool