Motorola XTS 2500 Service Manual page 230

6.3-16
6.3.17UHF Range 2 Receive RF Troubleshooting Chart
NOTE: INJECT MODULATED ON CARRIER
FREQUENCY SIGNAL AS REQUIRED.
If present
No
Check
at U401,
FL51
pin 47?
Yes
Check tank
Is
components L411,
2nd IF on
No
L412, C476.
U401, pins 4
Check for 3Vdc
and 5?
at pin 48
Yes
Before replacing U401,
check U401 voltages.
Check for no RX audio
VOCON flowchart
UHF R1 Band :
0.8 - 4.5V
If voltages are not OK,
check U102, (PCIC)
February 14, 2012
UHF2 Troubleshooting Charts: UHF Range 2 Receive RF Troubleshooting Chart
Bad SINAD
No Recovered
Audio
Spray or Inject 1st IF
into XTAL Filter FL51
UHF2 1st IF:73.35MHz
UHF2 2nd IF:2.25MHz
UHF2 2nd LO:71.1MHz
Audio
Heard?
Yes
Inject RF
into J101
Trace IF signal
Yes
IF Signal
from L10 to
at L54?
U401, pin 47
No
RF Signal
at C51?
No
RF
Check
Yes
Signal postselector
postselector
input C12?
voltage at R6
No
Check bias
Yes
RF Signal
voltages on
at C20?
Q29
No or
Weak RF
Check preselector filter.
RF
Program filter to test
Yes
Signal at preselector
freqs. and check
input TP1?
varactor voltages
for both preselector
& postselector No
Check harmonic
filter (Components placed
between C192 - C193)
and antenna switch
NOTE: The presence or absense of RF signals is generally not enough
to diagnose sensitivity degradations. It is best to compare signal levels
at each decision node, to the same circuit in working radio.
Inject -47 dBm into J101 and
No
toggle signal continuously
(on/off) while monitoring
TP403 data pulse
Does
the pulse
frequency
vary?
No
Remove SH401.
Check
Check 2nd LO
FGU Chart
Control Voltage at
U401, pin 38
No
1st LO
Yes
O/P OK?
Yes
Locked? VCO locked?
Yes
Check Mixer
16.8MHz
(U1) circuit
check at pin 35
on U401?
18MHz
at ABACUS
(U401) pin
20?
Yes
Before replacing U401, check 2nd
VCO Q401. Check VCO O/P level;
Disconnect R418 and verify that
a 0.5V to 5V control voltage VCO
will sweep about the IF frequency
Check IF
Yes
spectrum at
U401, pin 47
Check IF filter
Is it
No
FL51. Make sure
symmetric
LO is locked and
centered?
on frequency
Yes
See VOCON
chart, RX
audio problems
No
Check
No
FGU
Chart
Yes
Check U401 voltages,
No
programming, and
10MHz clock VCO
components
MAEPF-27342-O
6816985H01-F