Bose CD-20 Service Manual page 26

10. FM Stop Level Adjustment
Note: Do not perform the following test for
PCB 250736.
10.1 Inject an RF signal into the FM an-
tenna ternimals at 25 dBf, L+R modulation,
pilot off, set to 98.1 MHz.
10.2 Connect a DC meter to pin 21 of
U300.
10.3 Rotate R439 counterclockwise until
the voltage becomes less than 2.5V, then
clockwise until the voltage becomes greater
than 2.5V. The correct adjustment is when
the voltage just becomes sightly greater
than 2.5V.
10.4 Increase the RF generator to dBf and
confirm that the voltage at pin 21 U300 is
less than 2.5V.
11. FM Sensitivity / SNR
11.1 Inject an RF signal into the FM an-
tenna terminals at 42 dBf, L=R modulation,
pilot on.
11.2 Connect a dB meter to the TAPE
output. Reference the dB meter to this
point.
11.3 Turn the modulation off and measure
the output. The output should be ≤ -50 dB
for US versions and ≤ -45 dB for European
versions.
12. AM RMS
12.1 Inject an RF signal at a field strength
of 70 dBu into the AM antenna terminals.
12.2 Connect an AC meter to the tape
output.
12.3 Tune the generator and the unit t
630 kHz. Adjust the black slug of T302 for
maximum output. The output should be
≥ 300 mVrms.
TEST PROCEDURES
26
12.4 Tune the generator and the unit to
1080 kHz. Adjust the brown slug of T302
for maximum output.
12.5 Repeat steps 12.3 and 12.4 until
maximum output is obtained.
13. AM Sensitivity
13.1 Inject an RF signal, 1080 kHz, at a
field strength of 70 dBu to the AM antenna
terminals.
13.2 Connect a dB meter to the TAPE
output and reference it to this point.
13.3 Remove the RF signal and measure
the TAPE output (should be ≤ - 30 dB).
14. AM Stop Level adjustment
14.1 Inject an RF signal at a field strength
of 59 dBu to the AM antenna terminal.
14.2 Connect a DC meter to pin 21 of
U300.
14.3 Rotate R348 counterclockwise until
the voltage becomes less than 2.5V, then
clockwise until the voltage becomes greater
than 2.5V. The correct adjustment is when
the voltage just becomes slightly greater
than 2.5 VDC.
14.4 Increase the generator output to 64
dBu and confirm the voltage at pin 21 of
U300 is less than 2.5V.