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

Model 3400A
g. Place the red dots on the thermocouples face
down on the A4 Video Amplifier Board.
one of the thermocouples has an additional
colored dot place it in the TC402 position.
Carefully insert 'new thermocouple leads and
h.
solder.
i. Reverse steps e . d. c. b.
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 - 1 5 .
5 - 3 9 . CHECKING PHOTOCHOPPER ASSEMBLY A5.
The following procedure should
also be performed after replac­
ing a neon subassembly to verify
proper JX)sition of neons.
5-40. The following procedure verifies proper oper­
ation of the Photochopper Assembly.
chopper fails any of the tests below replace the entire
Photochopper Assembly (-hp- Part No. 1990-0223) or
the neon subassembly (-hp- Part No.
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 AS.
b. Lift the following component leads from the
A6 board.
Negative side of C601
Positive side of CG05
Negative side of e60S
Base of Q605
c . Place the A S board o n a programmable ex­
tender board (-hp- Part No.
Remove pin 13 lead on extender board closest
to the A6 board.
d. Place a 1 jiF 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.
indicate > 10 kQ (this checks the dynamic
series resistance of the modulator).
g. Turn off the 3400A, and disconnect ohmmeter.
h. Ground pin 1 3 on AS board.
meter between ground and junction of V501
and V502.
01768-3
If
Note: the violet
If
the Photo­
1990-0224)
5060-6038).
'
The ohmmeter should
Connect ohm­
i. Turn on the 3400A.
indicate < 7 kf! (this checks the dynamic
parallel resistance of modulator) .
Turn off the 3400A.
j.
tions made in step h.
k. Connect ohmmeter between ground and V503
lead going to base of Q605.
1.
Turn on the 3400A.
indicate > 10 kG (this checks the dynamic
series resistance of demodulator).
m. Turn off the 3400A.
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.
indicate < 10 kG (this checks the dynamic
parallel resistance of demodulator).
p. Turn off the 3400A.
and reconnect all component leads disconnec­
ted in step b.
Replace chopper amplifier board.
q.
5-41. REPLACEMENT OF NEON SUBASSE MBLY
-hp-
5-42. To replace neon subassembly.
follows:
Remove chopper amplifier assembly (A6).
a.
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 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.
d.
Clean the neon lamps with a
tissue to remove finger prints
before inserting new neon sub­
assembly in photochopper block.
e. With a new neon subassembly, feed the cable
through the hole in the PC board.
new neon subassembly into photochopper
block in the same orientation as the old neon
subassembly.
Section V
The ohmmeter should
Disconnect all connec­
The ohmmeter should
Disconnect ohmmeter.
The ohmmeter should
Disconnect ohmmeter
proceed as
Place the
5 - 1 5