PCP520R Rev0
(4D35/4C35/3255/3905 Service Manual)
Page 2 of 3
16. Replace the instrument cover and connect
the power cord.
17. Turn on the instrument and verify correct
thermoelectric operation using the test
utility “A/D Test” (see user’s guide).
E
F
block (E) facing the left side. Use #6x1/2
screws and large flat washers to secure
swaged end of standoffs to the rear wall,
using the old transistor mounting holes.
15. Plug the old transistor lead holes using
the ¼” plastic hole plugs (F).
4C3 and 3900 Instruction:
1. Turn off the instrument power and discon-
nect the power cord.
2. Remove the intrument rear cover.
3. Locate transistor Q3 on the transistor heat
sink mounted to the bottom of the chassis.
Q3 is the transistor 2nd from the left.
4. Remove the screws securing the heat sink
to the chassis and gently lift out the heat
sink.
5. Remove the screws holding the old tran-
sistor and insulating materials.
6. Remove the old transistor and insulating
materials by gently prying with a flat-
bladed screwdriver.
7. Remove the transistor socket Q3 from the
heat sink and clear the mounting holes of
any remaining hardware.
8. Cut transistor socket Q3 from harness
4C3160.
9. Strip wire insulation ¼” on four (4) wires
formerly soldered to the transistor socket.
Twist the stripped ends to prevent fraying.
10. Install the hex standoffs to PCB520 using
#6x3/8 screws, with the flat end of the
standoff against the board.
11. Connect red/white wire to terminal 1 (G).
12. Connect white/brown wire to terminal 2
(H).
13. Connect white/green wire to terminal 3 (I).
14. Connect black wire to terminal 4 (J).
15. Install completed assembly on the back
side of the heat sink where the previous
transistor socket was mounted. Use
#6x1/2 screws and large flat washers to
secure swaged end of standoffs to the heat
sink, using the old transistor mounting
holes. The ¼” plastic hole plugs are not
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