Table of Contents
Model 3476A
SECTION
VII
TROUBLESHOOTING AND
CIRCUIT
DIAGRAMS
7-1. INTRODUCTION.
7-2. This section contains preliminary troubleshooting in-
formation, printed circuit assembly exchange information,
schematic notes and reference designators, and schematic
diagrams of the Multimeter and Power Supply circuitry.
WARNING
1
These servicing instructions are for use by quali-
fied service personnel only. To avoid electrical
shock or damage to the instrument, do not
perform any servicing other than that contained
in the operating instructions unless you are
qualified to do so.
7-3. PRELIMINARY TROUBLESHOOTING.
The hybrid circuits in the Multimeter may be
permanently damaged by static discharge from
a hand or tool when the Multimeter is disas-
sembled. The procedures below must be fol-
lowed to prevent possible damage.
I. Ground the hand while disassembling and
working on the Multimeter. Conductive wrist-
bands (-hp- Part No. 00970-67900) are avail-
able for this purpose.
2. Attach the Multimeter COM terminal to
earth ground. Touch all tools to earth ground
to remove static charges before using them on
the Multimeter.
3. Use a soldering iron with a grounded tip.
Wear clean cotton gloves when working on the
circuit board. Contamination or fingerprints
will reduce the accuracy of the Multimeter. Use
low
flux
content
solder (-hp-
Part
No.
8090-0512) when replacing componenets. Do
not permit traces of flux to form on the circuit
board. Observe precautions against static dis-
charge. Do not use flux remover.
Section VII
7-4. Check to ensure the Multimeter is properly powered as
indicated by the decal on the side of the instrument.
7-5. If the display illuminates and indicates near zero re-
gardless of the input applied check the appropriate Multi-
meter input protection fuse.
Volts/Ohms input protection fuse:
1/32 A (250 V) -hp- P/N 2110-0420
Littlefuse P/N 312.031
Amps input protection fuse:
1
1
/
2
A(250 V)
-hp- P/N 2110-0043
Bussman AGC 1 -
1
/
2
Littlefuse 312.01.5
7-6. If input fuses are not at fault, proceed to disassemble
the Multimeter as follows:
a. Disconnect the power cord.
b.
Remove the input protection fuses located behind
the sliding input panel.
c. Place the Multimeter upside down on a grounded
work surface and remove the two screws from the bottom
cover.
d. Remove the bottom cover.
e. Connect a jumper across the amps input protection
fuse holder and across the ohms input protection fuse
holder.
If it is necessary to handle the printed circuit
assembly, hold it by the power transformer and
the front panel switch pushbuttons to avoid
contamination of the assembly.
WARNING
Disconnect the AC line cord before checking or
replacing the AC line fuse.
7-1
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