Advanced Instruments 3900, Service Manual

Page: 145 / 184

PCB520 Transistor Replacement Instruction
35010 to PCB520R Substitution
(Models 4D3, 3D3, 3250, 4C3, 3900, and 4250)
Reference: Use this instruction to install part
PCB520R, which is intended as a
direct replacement for part 35010
metal can FET transistor used on
some of the above models.
Materials Included:
1 - PCB520 assembly
2 - H50606, #6x3/8 Sems
2 - H50608, #6x1/2 Sems
2 - H63093, #6 large flat washers
2 - 90049, Hex swage standoffs
2 - 91038, ¼” plastic hole plugs
Tools Needed:
Wire cutters, wire strippers,
small flat-bladed screwdriver,
medium Phillips screwdriver.
Warning-Hazardous Voltage
Warning-Internal components may be
damaged by static electricity.
4D3, 3D3, 3250, and 4250 Instruction:
1. Turn off the instrument power and discon-
nect the power cord.
2. Remove the intrument cover.
3. Locate transistor Q1B on left-rear of the
chassis. Q1B is the transistor nearest to
the top of the rear panel.
4. If your instrument already has PCB520 in
this location, remove the old PCB and
skip to step 11.
5. Remove the screws securing the protec-
tive black plastic cap on the outside rear
of the instrument.
For additional information or technical assistance,
please contact Advanced Instruments Hot-Line
®
Service Center (U.S. 1-800-225-4034, outside North
AUS 1-781-320-9000).
6. Remove the old transistor and insulating
materials by gently prying with a flat-
bladed screwdriver.
7. Remove the transistor socket Q1B from
the rear panel and clear the mounting
holes of any remaining hardware.
8. Cut transistor socket Q1B from harness
M20150.
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 white/red wire to terminal 1 (A).
12. Connect white/brown wire to terminal 2
(B).
13. Connect brown wire to terminal 3 (C).
14. Connect black wire to terminal 4 (D).
Note:
Make sure screw terminals are tight
and that only bare wire, not insulation,
is captured in the clamp.
PCP520R Rev3
(4D35/4C35/3255/3905 Service Manual)
Page 1 of 3
A
B
C
D
E