Model 8903B
TROUBLESHOOTING---SERVICE SHEET
4
Service
Hint:
Q8
shoiild be
on.
10.
On the Audio Analyzer,
key
in 0.565 SPCL to disable the discharge of the Tune and Balance Integrators.
Connect one channel
of
the
oscilloscope (ac coupled) to A3TP5 and the other channel to
pin
2
of U9. Trigger
the oscilloscope from the signal
on
A3TP5
(BP
OUT). The two signals should be in phase. (The signal to pin
2
ofU9 should have an amplitude of approximately
100
mVpp.)
11.
On
the Audio Analyzer,
key
in FREQ
500
Hz. The two signals should be approximately
180"
out of phase.
12.
On
the Audio Analyzer, key in FREQ
1
kHz. Move the oscilloscope from A3TP5 to A3TP6
(HP
OUT) and
from pin
2
of U9 to pin
2
of U4. The two signals should be in phase.
13. On the Audio Analyzer,
key
in
44.3 SPCL. The two signals shoiild be approximately
180"
out of phase.
14.
On
the Audio Analyzer, key in 44.2 SPCL. Connect the oscilloscope to the source of Q2.
The
waveform
should have
an
amplitude
of
less than
200
niVpp.
Hint: Pin 14
of
UlOD
shoiild be OV. Q2 should be
on.
15.
On the Audio Analyzer,
key
in AMPTD
100
mV. Key
in
3.3 SPCL to set the Gain Switch off. The waveform
should be a sine wave with a phase reversal at each peak and have an amplitude of approximately
5
Vpp.
Hint: Pin 14 of UlOD should be -15V. 42 shoiild be
off.
Hint: The signal at A3TP2 slioiild be a sine wave with
an
amplitude of 16 Vpp.
If
faulty, see Service Sheet
5
and check Attenuator
1.
16.
Connect the oscilloscope
to
the soLirce of 43. The waveform should be a positive, full-wave-rectified sine
wave wit.h an amplitude of approximately
2
Vpp.
Hint:
43
should be off.
17.
On
the Audio Analyzer,
key
in
3.1
SPCL. Key in AMPTD
1
V.
The signal amplitude should be less than
500
mVpp.
Hint:
43
should be
on.
NOTE
The.
following
.slc'p.~
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varioiis
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Thc
noldi
circiiilry
OJ'
Scrvicc Shwl
3
is
a.s.siimc~l
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opcralirig properly, and (hc
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lo
havc
less
lhan
O.Ol?b
di.slorrion
and
noise. If'dislorfion
is
high
on
all
ranges, pcv~jbrrn fhe
Notch Filter Tune and Balance Adjustment,
paragraph
3-12,
and ah chwk fhc di.,lorlion oj'lhc Oiilpiil
A
rnpl(ficr
I,
.stv
Scvviw Shw!
5.
18.
On
the Audio Analyzer, press DISTN. Key in AMPTD
2.5
V.
Key in 44.1 SPCL
to
set the Notch Filter
to
the notch mode. Key in 3.0
SPCL
to
set the output amplifier gain to automatic. The amplitude display should
read
0.01%
or less.
Hint: The gates of
47
and Q9 should be
OV
and the FETs should be
on.
The gates of Q6 and QlO should be
-
15V and the FETs should be off. The signal at A3TP7 (OUT) should be less than
100
mVpp.
19.
On the Audio Analyzer,
key
in 54.139
SPCL.
Note the amplitude display. Key in 54.155 SPCL. Note the
amplitude display.
In
both cases the display should be
O.OIo/o
or less.
20.
On
the Audio Analyzer,
key
in FREQ 20 Hz. Key in 53.0 SPCL and 54.23 SPCL to tune the Notch Filter
to
20 Hz.
The amplitude display should be
0.01Yo
or
less.
Hint: The gates of Q6 and QlO should be
OV
and the FETs should be on. The gates of
47
and Q9 should be
-
15V and the FETs should be off. The signal at A3TP7 should be less than
100
mVpp.
8B-37
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