Service Model 8903B
Hint:
If
the signal amplitude is only slightly out of limits, perform the Voltmeter Adjustment, paragraph 5-13;
if
greatly out of limits, perform the
@
fill-
Waue Rectfier Check and the
@)
Log
Amplifier and Filter Amplifier
Check.
4. Key in 5.2 SPCL
to
switch the detector to average. The level on the voltmeter should be between +2.94 and
+3.06 Vdc. Grounding pin 2 of U22 should cause the level to go to approximately -15 Vdc.
Hint: Pin 10 of U23 should be a TTL high. U23B, U23D, U24B, and U24D should be
off.
U23A, U23C, U24A,
and U24C should be on.
5.
Reconnect the voltmeter to A4TP4. Set the voltmeter
to
measure ac. On the Audio Analyzer, reduce the
SOURCE amplitude for a reading between 299 and 301 mVrms on the voltmeter.
6. Reconnect the voltmeter to A4TP1.
Set
the voltmeter to measure dc. The level on the voltmeter should be
between 3-294 and +306 mVdc.
Hint:
If
the signal is only slightly out of limits, perform the Voltmeter Adjustment, paragraph 5-13;
if
within
limits, the detector
is
functioning properly under the current
test
conditions.
7.
Key in
5.0
SPCL
to
switch the detector
to
rms.
The level on the voltmeter should be between +294 and +306
mVdc.
8. Reconnect the voltmeter
to
A4TP4. Set the voltmeter to measure ac. On the Audio Analyzer, increase the
SOURCE amplitude for a reading between 2.99 and 3.01 Vrms on the voltmeter.
9.
Key in
5.7
SPCL to switch the detector
to
quasi-peak. Hint: Pin 3 of U29 should be a TTL low. U25A, U25B
and U25C should be on, U25D should be
off
and U23 and U24 should be in the same state as for the average
detector. See hint for step 4.
10.
Reconnect the voltmeter
to
A4TP1. Set the voltmeter
to
measure dc. The level on the voltmeter should be
between 2.94 and 3.06 Vdc. Hint: See the hint for step 6.
11.
Disconnect the voltmeter. Connect
a
high-impedance, dc-coupled oscilloscope to A4TP1. Use the oscilloscope’s
vertical gain controls to adjust the diplay amplitude for 4 division peak deflections of the dc signal. Hint: Set the
ground
to
the center of the display. Set sweep time
to
1
sec/div. Hint: See the hint for step 6.
12.
On the Audio Analyzer, press
S
(Shift) SIG/NOISE. The waveform should be as shown in Figure 8B-33.1.
Note
rise and fall times.
(J2)
Full-Wave
Rectifier
Check
1.
On the Audio Analyzer, key in 41.0 SPCL to initialize the instrument. Set the INPUT and OUTPUT switches
to
ground. Key in AMPTD 3
V.
Key in
1.11
SPCL to set the input gain to
0
dB.
Key in 3.1 SPCL to set the
output gain to
0
dB.
Connect the HIGH OUTPUT
to
the HIGH INPUT.
2.
Connect
a
high-impedance, dc coupled oscilloscope to A4TP4 (AMP
4).
On the Audio Analyzer, fine adjust the
SOURCE amplitude for
8.5
Vpp on the oscilloscope.
Hint: The amplitude at A4TP4 before adjustment should be approximately 8.5 Vpp.
If
the signal
is
faulty, see
Service Sheet
5
and check the Output Amplifier circuitry.
3. Connect the oscilloscope to pin 6
of
U5. The waveform should be as shown in Figure 8B-34.
(Note:
Excessive
input capacitance of the oscilloscope may cause oscillation. Use a divide-by-ten probe.)
4. Connect the oscilloscope to A4TP11 (RECT). The waveform should
be
a negative full-wave-rectified sine wave
with a peak amplitude between -4.5 and -4.OV.
8B-46
rev.20JUN87
To Next Page
Loading...
