Base Of Q601 - HP 3400A Operating And Service Manual

Model 3400A
Section
V
Table 5-6. Troubleshooting Procedure
(Cont'd)
CHECK
PROCEDURE
ACTION
@
Investigate Q604, C605, (and
demodulator),
V503
and V504. See Paragraph 5-39
for
photochopper
check.
Check
chopper neon
voltage.
Refer
to
Figure 5-9
for
waveform.
See check
number
(Tl)
for
details.
@
Investigate
Q603 and
associated
circuit.
@
Increase the level
of
the inserted signal to +0.-2
Vdc.
Measure
the ac signal
at
the
base
of
Q601.
Refer
to
Figure 5-12
for
waveform.
PASSES: Proceed
to
FAILS: Proceed
to
© ©
j~j"i_n
BASE OF
Q601
+
.
2Vsignal through 499
kfi
resistor to pin 13 on
A6
Sweep
= 5
ms/cm
Vertical =
5
mV/cm
AC
coupled
no probe required
Figure
5-12.
Base
of
Q601
(feedback loop open)
Table 5-6. Troubleshooting
Procedure
(Cont'd)
CHECK
PROCEDURE ACTION
©
Investigate
Q601
and associated
circuit.
©
Investigate V501, V502, C601,
C602 and
R601.
See
Paragraph 5-39
for photochopper check.
Check chopper neon
voltage.
Referto Figure 5-9
for
waveform.
See check
number
(ll)
for
details.
©
Measure
the ac signal
at
the output
of
impedance
converter
A2
(negative side
of
C205).
The reading
should be approximately
0.
96
mV
rms.
PASSES: Proceed
to
FAILS: Proceed
to
©
@
Measure
the ac signal
at
the input to
video amplifier
A4
positive side
of
C402.
The
reading should be
approximately
0.
96
mV
rms.
PASSES: Proceed
to
FAILS: Proceed
to
(28)
@
.
Measure
the ac signal
at
the
base
of
Q404.
The
reading should be approximately 155
mV
rms.
PASSES: Proceed
to
FAILS: Proceed
to
©^
©
01768-3
5-13