HP 3400A Service Manual

Maintenance
Table 5-5. Front Panel Symptoms
Check for a defective oscillator on the A6
assembly.
Reading far out of tolerance, meter pegged
out.
Excessive
offset
(>8%)
with
input
A6R626
and/or
C405
misadjusted.
shorted.
Q401 or Q402 shorted.
400Hz calibration low and frequency
response falls off above 50KHz.
Check collector voltage of Q2Z01 ‘should
not exceed 9.0V)
Switching transients exceeds 5% of full
scale with shorted input.
Check Q201, Q401, Q402, and TC401.
See paragraph 5-34 for details on TC401.
Instrument has been overloaded.
Noisy chopper op amp (U601).
Meter jitty.
Check resistors in second attenuator.
Full-scale difference from range to range.
Check thermocouples. See paragraph
5-35 for details.
Meter pegs full scale.
Replace thermocouples. See paragraph
5-38.
Overshoot, undershoot, or sluggish
response on meter.
Check ac feedback on the A6 assembly
(R614, C605, and R615).
Meter moves rapidly from zero to full-scale
and back.
Model 3400A
5-37.
The
thermocouple
tests
consist
of
checking
the
heater
resistance
and
output
voltage
of
each
thermocouple.
The
heater
resistance
is
checked
using
an
ohmmeter.
The
output
voltage
is
checked
by
supplying
5
mA
dc
current
to
the
heater
and
then
measuring
the
output
voltage.
If
the
thermocouple
fails
any
of
the
tests,
replace
it
using
the
procedure
in
paragraph
5-38.
A
Digital
Multimeter
(like
the
-hp-
Model
3468A/B),
a
10
V
de
power
supply
(like
the
-hp-
Model
6214B),
and
a
1
Kohm
+0.1%
resistor
(-hp-
Part
Number
0698-7449)
are
needed
for
the
tests.
Refer
to
Figure
5-5
while
performing
the
following
procedure.
a. Turn the 3400A off and remove the A6 assembly.
b.
Set
the
digital
multimeter
to
the
ohms
function.
Connect
the
test
leads
between
chassis
ground
and
the
junction
of
C413
and
C415
on
the
A4
assembly.
This
checks
the
heater
resistance
of
TC401.
The
multimeter
reading
should
be
between
76.5
ohms
and
103.5
ohms.
If
the
readings
are
out
of
the
specified
limits,
replace
the
matched
pair
of
thermocouples
(-hp-
Part
Number
0863-0003).
5-12
NOTE
The
following
check
applies
to
-hp-
3400A’s
with
serial
number
_prefix
2225
and
above.
For
instruments
that
have
a
lower
prefix,
change
step
c
to
the
following:
c.
Connect
the
multimeter
between
the
clear
lead
on
R4
(CAL
poten-
tiometer
on
chassis)
and
pin
14
on
the
A6
socket.
This
checks
the
heater
of
TC402.
Make
sure
the
reading
is
between
76.5
ohms
and
103.5
ohms.
Replace
the
thermocouples
if
out
of
limits.

HP 3400A Specifications

General

Brand	HP
Model	3400A
Category	Measuring Instruments
Language	English