TM 10-6630-245-13&P
4.4. PHOTOCELL REPLACEMENT.
This task covers:
a.
Test
b.
Replacement
INITIAL SETUP
Materials/Parts
Photocell Assembly, PN MSI- 1108-1, See Appendix C
Tools
Tool Kit, General Mechanics, Automotive, See Appendix B
Multimeter, 0-5000 Volt, See Appendix B
a.
Test
WARNING
High voltage used with Spectrophotometer. Misuse can cause electrical shock and damage
equipment. When operating with 115V or 220V power, make sure the power source and
equipment are in ground potential. Ensure that the power cable connections are correct for the
desired voltage power before connecting the power source.
(1)
Ensure that the unit is properly connected
for dc operation. See paragraph 2.6.2.3
b.
(2)
Check operation by testing the ZERO
ADJUST knob(11, fig. 2-5) with on/off
toggle switch(l2) at ZERO CHECK (para
2.6.2.6).
(3)
Loosen the two thumbscrews(9) on the
front panel. Turn the unit on its left side,
and gently pull the panel away from the
case (see para 2.6.2.3).
NOTE
Before removal, note position of
wires and plug on photocell cable.
(4)
Disconnect
the
photocell
assembly
cable(3, fig. 4-3) from the amplifier board
at
BC2(2).
Set
multimeter
to
50
microampere range. Connect the positive
lead to the photocell cable(3) shield (black
wire). Connect negative lead to the
center conductor (white wire).
Figure 4-3. Photocell Replacement.
(5)
Set the Spectrophotometer wavelength dial(8, fig. 2-5) to 700 nm. Turn the on/off toggle switch(12) to
ON. Rotate the LIGHT CONTROL knob(l0) fully clockwise. The multimeter should indicate a reading
greater than 5 microamperes.
CAUTION
Be sure that photocell cable wires and plug are in correct position or damage may occur to the
Spectrophotometer.
(6)
If ok, reconnect photocell cable to the amplifier board at BC2(2, fig. 4-3). Replace front panel and ensure
that the unit is properly connected. See para 2.6.2.3.a. for ac operation; see para 2.6.2.3.b. for dc
operation. If not ok, replace the photocell as described below.
4-6
