4.4. PHOTOCELL REPLACEMENT.
This task covers:
Photocell Assembly, PN MSI- 1108-1, See Appendix C
Tool Kit, General Mechanics, Automotive, See Appendix B
Multimeter, 0-5000 Volt, See Appendix B
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.
Ensure that the unit is properly connected
for dc operation. See paragraph 22.214.171.124
Check operation by testing the ZERO
ADJUST knob(11, fig. 2-5) with on/off
toggle switch(l2) at ZERO CHECK (para
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 126.96.36.199).
Before removal, note position of
wires and plug on photocell cable.
cable(3, fig. 4-3) from the amplifier board
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.
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.
Be sure that photocell cable wires and plug are in correct position or damage may occur to the
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 188.8.131.52.a. for ac operation; see para 184.108.40.206.b. for dc
operation. If not ok, replace the photocell as described below.