4. Apply a standard input signal to the module input. (-60
dBm, 21.4 MHz signal modulated with 1 kHz AF, 3
kHz peak deviation)
5. Monitor TP5 with a high-impedance probe connected to
the frequency counter. Adjust L10 for a reading of 455
kHz
±
100 Hz.
6. Set VRI for 1 Vrms
±
3% at module output (pin 31C on
96 pin connector J2).
TROUBLESHOOTING
When troubleshooting the module, it is most convenient if
the standard test fixture is used. The following conditions are
with the module in the 25 kHz mode. This can be set up using
a PC with the necessary software connected to the test fixture.
Alternatively, a wire link can be soldered between holes H1
and H2 on the PC board.
IF amplifier Q2 has a nominal 8 dB gain. U1 has a nominal
gain of 30 dB. The mixer has about 2 dB loss with proper LO
injection. The proper crystal oscillator level is 10 mV pk meas-
ured at TP3.
The following four test points are provided on the PWB for
additional test capability:
TP1:
60 mV pk @ 21.4 MHz with -30 dBm input signal
TP3:
10 mV pk @ 20.945 MHz independent of input sig-
nal
TP4:
20 mV pk @ 455 kHz with -60 dBm input signal
TP5:
750 mV pk @ 455 kHz with -60 dbm input signal
All RF voltages measured with 10 Megohm, 11 pF probe.
ASSEMBLY DIAGRAM
TROUBLE SHOOTING GUIDE
SYMPTOM
CHECK
(CORRECT READING SHOWN)
INCORRECT READING
INDICATES DEFECTIVE
COMPONENT
Fault indicator on
Check DC voltages
+8V at U8 Pin 1
+4v at U6 Pin 7
5.5V at U1 output pin
6V at U3 Pin 5
If DC voltages not correct
U8 or associated components
U6 or associated components
U1 or associated components
U3 or associated components
If DC voltages correct
U4, U5, U6, DI, Q3, Q4, Q5
No audio - no noise
With no signal applied to module IF input
Check for AF noise @ C29 ; 200mV
Check for AF noise @ U6 Pin 14:1 V
U3 or associated components
U6 or associated components
Noise only - no
demodulated audio
Check crystal oscillator: TP3 10 mVpk 20.945 MHz
Apply-30 dBm 21.4 MHz input, check TPl 60 mVpk
Apply-60 dBm 21.4 MHz input, check TP4 20 mVpk
U3, Y3 or associated components
Q2, Y1, U1 or associated components
U3, FL1 or associated components
Poor 12 dB SINAD
Check crystal oscillator: TP3 10 mVpk 20.945 MHz
Apply-30 dBm 21.4 MHz input, check TP1 60 mVpk
Apply-60 dBm 21.4 MHz input, check TP4 20 mVpk
U3, Y3 or associated components
Q6, Y1, U1 or associated components
U3, FL1 or associated components
No squelch
function
With squelch pot maximum, or with module AUDIO/
SQUELCH/HI connected to SQUELCH/ARM input
and with no signal to module IF input:
Check Presence of 1 Vpk noise at U6 Pin 14
Check presence of 1 Vpk noise U7 at Pin 1
Check DC voltage U7 at Pin 8: 7V
Check DC voltage U7 at Pin 14: 0.5V
U6 or associated components
U7 or associated components
RECEIVER IF MODULE
19D902783G7, G11
(19D902783, Sh. 1, Rev. 3)
LBI-39123E
3
Summary of Contents for 19D902783G1
Page 6: ...SCHEMATIC DIAGRAM RECEIVER IF MODULE 19D902494G1 19D902504 Sh 1 Rev 6 LBI 38643C 5...
Page 7: ...SCHEMATIC DIAGRAM RECEIVER IF MODULE 19D902494G1 19D902504 Sh 2 Rev 6 LBI 38643C 6...
Page 42: ...RECEIVER FRONT END BOARD 19D902490G4 G7 OUTLINE DIAGRAM 19D902490 Sh 4 Rev 6A LBI 38673F 5...
Page 43: ...ASSEMBLY DIAGRAM RECEIVER FRONT END MODULE 19D902782G3 19D902782 Sh 1 Rev 6 LBI 38673F 6...
Page 44: ...ASSEMBLY DIAGRAM RECEIVER FRONT END MODULE 19D902782G4 G7 19D902782 Sh 2 Rev 6 LBI 38673F 7...
Page 45: ...SCHEMATIC DIAGRAM RECEIVER FRONT END MODULE 19D902782G4 G7 19D904768 Sh 1 Rev 6 LBI 38673F 8...
Page 47: ...SCHEMATIC DIAGRAM RECEIVER FRONT END MODULE 19D902782G3 19D903498 Rev 7 LBI 38673F 10...
Page 48: ...This page intentionally left blank LBI 38673F 11...
Page 56: ...ASSEMBLY DIAGRAMS LOW PASS FILTER MODULE 19D902856G3 19D902856 Sh 1 Rev 0 LBI 38674F 7...
Page 71: ...ACCESSORIES ANTENNA SWITCH 19B235897P2 LBI 38675E 9...
Page 80: ...SCHEMATIC DIAGRAM RECEIVER IF MODULE 19D902494G7 G11 193D1065 Sh 1 Rev 3 LBI 39123E 7...
Page 81: ...SCHEMATIC DIAGRAM RECEIVER IF MODULE 19D902494G7 G11 193D1065 Sh 2 Rev 3 LBI 39123E 8...
Page 82: ...SCHEMATIC DIAGRAM RECEIVER IF MODULE 19D902494G7 G11 193D1065 Sh 3 Rev 3 LBI 39123E 9...