Neon Drive Voltage - HP 3400A Operating And Service Manual

Model
3400
Section
V
Table
5-6.
Troubleshooting Procedure
(Cont'd)
CHECK PROCEDURE ACTION
®
©
Investigate Q605,
CR604, and
R615.
Investigate
demodulator V503 and V504. See
Paragraph 5-39
for
photochopper check. Check
chopper neon
voltage.
Refer
to
Figure
5-9
for
waveform. Current
variation
through neons
may
cause meter
jitter.
For proper chopper
action,
neon
firing potential
(most negative point on
wave-
form)
is
normally between 50V and 60V.
If
the
waveform
displays noise (nonlinearity) at
both
extremities,
jitter
will
occur on
the
meter.
If
the
waveform displays a noise replace
the
neon
subassembly as outlined
in
Paragraph
5-41.
PIN
3
OR
5
ON
A6
Sweep
=
2
ms/cm
Vertical =
20V/cm
DC
coupled
use
10:1
probe
Figure
5-9.
Neon
Drive Voltage
»
Table
5-6.
Troubleshooting Procedure
(Cont'd)
»
CHECK
PROCEDURE
ACTION
©
Measure
the ac signal
at
collector
of
Q602.
Refer
to
Figure 5-10
for
waveform.
PASSES: Proceed
to
@
FAILS: Proceed
to
@
01768-3
5-11