Checking Photochopper Assembly A5; Replacement Of Neon Subassembly - HP 3400A Operating And Service Manual

1
Model 3400A
g.
Place
the
red dots
on
the
thermocouples
face
down
on
the
A4
Video Amplifier Board.
If
one
of
the
thermocouples has an
additional
colored
dot
place
it
in the
TC402
position.
h.
Carefully insert
new thermocouple
leads
and
solder.
i.
Reverse
steps
e, d,
c,
b.
Note: the violet
lead
goes
to the
lower
of
the
two top connec-
tors
on
the
A4
board.
j.
After
thermocouple replacements perform a
complete adjustment and
calibration
pro-
cedure
as outlined in
Paragraph 5-15.
5-39.
CHECKING
PHOTOCHOPPER ASSEMBLY
A5.
NOTE
The
following
procedure
should
also be
performed
after
replac-
ing
a neon subassembly
to verify
proper
position
of
neons.
5-40.
The
following
procedure
verifies
proper oper-
ation
of
the
Photochopper Assembly.
If
the
Photo-
chopper
fails
any
of
the tests
below replace the entire
Photochopper
Assembly
(-hp-
Part No. 1990-0223) or
the
neon subassembly
(-hp-
Part No.
1990-0224)
according
to
procedures
outlined in
Paragraph
5-41.
See Figure 5-9
to
check operation
of
the neons.
To
check
the
photochopper
assembly proceed
as follows:
a.
Remove
the
Chopper Amplifier board A6.
b.
Lift
the following component
leads
from
the
A6
board.
Negative side
of
C601
Positive side
of
C605
Negative
side
of
C606
Base
of
Q605
c.
Place
the
A6
board on a programmable
ex-
tender board
(-hp-
Part No. 5060-6038).
Remove
pin 13 lead on extender board
closest
to the
A6
board.
d.
Place
alfiF
capacitor (-hp-
Part No. 0180-
0269)
across the
input
leads
of
an
ohmmeter
(note the polarity
of
capacitor
and
ohmmeter
leads).
e.
Connect
the
ohmmeter
between
pin 13
and
ground.
f.
Turn
on the 3400A.
The ohmmeter
should
indicate
>
10 kft (this
checks
the
dynamic
series resistance
of
the modulator).
g.
Turn
off
the
3400A, and disconnect
ohmmeter.
h.
01768-3
Ground
pin 13
on
A6
board.
Connect
ohm-
meter between ground and junction
of
V501
and V502.
Section
V
i.
Turn
on the 3400A.
The ohmmeter
should
indicate <
7 kft (this
checks
the
dynamic
parallel resistance
of
modulator).
j.
Turn
off
the 3400A. Disconnect
all
connec-
tions
made
in step
h.
k.
Connect
ohmmeter
between ground and V503
lead going
to
base
of
Q605.
1.
Turn
on
the
3400A.
The ohmmeter
should
indicate > 10
kfi (this
checks
the
dynamic
series resistance
of
demodulator).
m.
Turn
off
the
3400A. Disconnect
ohmmeter.
n.
Ground V503
lead going
to
base
of
Q605 and
connect
ohmmeter between ground and
the
junction
of
V503 and
V504.
o.
Turn on
the
3400A.
The ohmmeter
should
indicate < 10
kJ2 (this
checks
the
dynamic
parallel
resistance
of
demodulator).
p.
Turn
off
the
3400A. Disconnect
ohmmeter
and
reconnect
all
component leads disconnec-
ted
in step
b.
q.
Replace chopper
amplifier board.
5-41.
REPLACEMENT OF NEON SUBASSEMBLY
-hp-
PART
NO.
1990-0224.
5-42.
To
replace neon subassembly, proceed as
follows:
a.
Remove chopper
amplifier
assembly
(A6).
b.
Disconnect the
photochopper
cable at pins
2,
3,
4,
and
5
on
PC
board.
c.
Remove two
phillips
head screws on
top
cover
of
the photochopper block.
NOTE
d.
Note
the orientation of
neon sub-
assembly.
The neon subassembly
does
not
lie flat
but at
an angle
within the photochopper block.
Remove
the
neon subassembly.
NOTE
Clean
the neon
lamps
with a
tissue
to
remove
finger prints
before inserting
new neon sub-
assembly
in
photochopper
block.
With a
new
neon subassembly,
feed the cable
through
the hole
in
the
PC
board.
Place
the
new
neon subassembly
into
photochopper
block
in the
same
orientation as
the old
neon
subassembly.
5-15