HP 3400A Service Manual

Maintenance
Model
3400A
i. Connect the power supply and 1 Kohm resistor between the clear
lead on R4 and pin 14 on the A6 socket. This checks the TC402
output voltage. Refer to Figure 5-5 and connect the HI lead of the
multimeter to point A and the low lead to point B (i.e., across the
resistor). Turn the power supply on and adjust it for a5 V reading
on the multimeter.
i.
Connect
the
power
supply
and
1
Kohm
resistor
between
pins
10
and
14
on
the
Aé6
socket.
This
checks
the
TC402
output
voltage.
Refer
to Figure
5-5
and
connect
the
HI
lead
of the
multimeter
to
point
A
and
the
low
lead
to
point
B
(i.e.,
across
the
resistor).
Turn
the
power
supply
on
and
adjust
it
for
a
5
V
reading
on
the
multimeter.
j. Disconnect the multimeter and connect as in step f.
k. Make sure the multimeter reading is negative and within 1 mV of the reading noted
in
step
g.
It
should
display
between
+6.5mV
and
+9
mV.
If
the
reading
is
out
of
the
specified
limits, replace the thermocouples.
1.
Disconnect
the
power
supply,
resistor,
and
multimeter
from
the
3400A.
Set
the
multimeter
to
the
ohms
function
and
connect
it
between
pins
11
and
14 on
the
A6
socket.
This
checks
for
thermocouple
shorts
to
ground,
through
the
cover.
If
the
reading
on
the
multimeter
is
below
200
Kohms,
look
for
a
short.
5-38. Thermocouple Replacement
Exercise
extreme
care
when
removing
or
replacing
the
amplifier
printed
circuit
board
assembly
and
when
shaping
the
thermocou-
ple
leads.
5-39. Should a thermocouple be defective, it is necessary to replace both as a matched pair
(see
Section
VII,
Table
of
Replaceable
Parts)
for
part
number.
To
replace
thermocouples,
perform the following steps: ;
a.
Turn
instrument
power
off
and
remove
right
side
(INPUT
side)
and
top
covers.
b.
Remove
the
four
lead
connection
to
the
A4
amplifier
board.
1.
Black
coaxial
cable
(two
leads)
2.
Violet
lead
3.
White
lead/blue
lead.
c.
Remove
the
three
mounting
screws
on
the
amplifier
board.
d.
Gently
pull
bottom
of
board
out
at
the
same
time
relieving
stress
on
thermocouple
cable
until
the
board
will
drop
down
and
the
top
will clear
main
frame.
Carefully
fold
board
down
to expose the four nuts holding the thermocouple shield.
e. Remove four shield nuts; lift shield off.. Remove thermocouples, noting orientation.

HP 3400A Specifications

General

Brand	HP
Model	3400A
Category	Measuring Instruments
Language	English