Adjust Rx Unit; Rx Test - Furuno NX-700B Service Manual

3. Adjust Rx Unit

Dot signals of 1700 Hz + 85 Hz and 100 bps are applied to the RCV board and
adjustments are made on the receiving FSK detection circuit (U4, 5: NJN221).
The section to be adjusted is VR shown below.
FSK Input
Preamp
Procedure
1. Execute "Rx Test" in [MENU] -> Initialize 1 menu.
2. In case of 518 kHz, adjust R60 so that the U4 output (U2-#3) has the duty ratio of 50
+ 5 %.
In case of 490 kHz or 4209.5 kHz, adjust R75 so that the U5 output (U3-#3) has the
duty ratio of 50 + 5 %.
Note:
When the duty ratio of B and Y signals differ, the received signal cannot be decoded
correctly. The tracking width of the received frequency becomes smaller than for
approximately (1700 Hz + 85 Hz) + 40 Hz.
RF
+12V
+9V
SW
AVR
LO SW DC
Test Signal
RD-B
RD-A
1700Hz+85Hz
Test OFF
Test Start

4. Rx Test

This test is the same as the receiving test in the setting of "[MENU] -> Service -> Test".
See page 7-3 for details.
Loop
O DET
FIL
VCO
L.D
O DET
FIL
Fig. 7.3.1 NJN221 Block Diagram
Test
Signal
RX
518kHz
490kHz
RX
4209.5kHz
MOD
RX Local-1
RX Local-2
Fig. 7.3.2 Adjustments of receiving circuit
7-13
7.3 Test in Initialize-1 and Initialize-2 menus
Data
FIL
VR
Not used:
Lock Detect Output
518kHz
TD-A/B
RX 1
518kHz
490kHz
RX 2
TD-A/B
490kHz
RCV (08P3227)
FSK Output
CPU
(08P3225)
NX-700A/B