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 Insert the LM324 14-pin chip into the socket at U4. If the LM324's two rows of pins are splayed
outward, carefully bend them inward slightly by laying the component sideways on a flat surface
and pressing gently. The pins should line up with the socket contacts. Be absolutely certain that
the notch or dimple in one end of U4 matches the notch in the end of the socket. The socket
notch is adjacent to the red LED4, as shown in this photo.

Figure 11: U4 LM324 orientation.
 Connect one end of your test lead to the Com pin on J3 or J5. You may disconnect the
multimeter's negative lead, or just use the free Com pin on the other header.
 Turn on the power. All four LEDs should light up. If yellow LED1 is off, adjust R2 until it lights. If
yellow LED3 is off, adjust R10 until it lights. If the red LEDs are off, don't worry about them now.
 Touch the free end of your test lead to the PCell (center) pin of J3. Yellow LED1 should turn off
each time the pin is touched. If not, check that the other end is actually connected to the Com pin.
Also check that U4 is inserted into its socket correctly, and that all pins are in their socket
contacts, not bent under or outward.
If U4 is inserted backward, turn off power , then remove it and insert it correctly. Turn on power
and try the test again. If the yellow LED still doesn't turn on, U4 is probably destroyed. Replace it
with a new LM324 from Radio Shack, Digi-Key (http://www.digikey.com) or Mouser Electronics
(http://www.mouser.com).
 Touch the free end of your test lead to the PCell (center) pin of J5. Yellow LED3 should turn off
each time the pin is touched. If not, check and correct the U4 items listed above.
With both yellow LEDs working, we can move on to the red LEDs. Do not proceed until the yellow
LEDs work, because U4 also controls the red LEDs.
 Leave 24one end of your test lead connected to the Com pin on J3 or J5.
 Touch the free end of your test lead to pin 1 of the empty socket for U1 (see Figure 12 below to
identify this pin). Red LED2 should turn off each time the pin is touched. If not, check and correct
the U4 items listed above. If LED2 is off when not touching the pin, skip this step – the “floating”
input to U4 is likely switching to the opposite state, producing a useless indication. This condition
will be corrected when U1 is installed in its socket.
LOC3 Dual Laser Occupancy Detector User Manual
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