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Section VII
7-7. If the instrument display did not illuminate, check the
ac line fuse.
ac line fuse:
1/16 A (250 V) - hp- Part No. 2110-0311
Littlefuse 313.062
Bussman MDL 1/16
7-8. Connect the 3476A TP ,Ç5, to earth ground.
7-9. Connect the appropriate ac line voltage as specified by
the option decal attached to the instrument.
WARNING
To avoid electrical shock, do not touch the ac
line fuse or the line voltage jumpers when the
instrument is plugged into ac power.
7-10. Power Supply Troubleshooting.
7-11. Measure the dc power supply voltages referenced to
the analog ground test point (TP j ). The dc voltmeter
indication at TP + 6 should be within the limits of 5.88 to
6.12 V dc. The dc voltmeter indication at TP - 4 should be
within the limits of 3.92 to 4.08 V dc. If these voltages are
correct, no further power supply checks are necessary.
7-12. If the TP + 6 and TP - 4 voltages are not correct,
check the dc voltage at the positive terminal of C15. This
voltage should be within the limits of + 15 to + 25 V dc
relative to TP
with less than 2 volts peak- to-peak ripple.
7-13. Verify that the power supply is not in a current limit
condition by checking the voltage drop across R52. This
voltage should be less than 0.36 V dc.
7-14. Display Troubleshooting.
7-15. Most problems with the display section can be iso-
lated by front panel observations. Note the display failure
symptoms prior to trouleshooting this section of the instru-
ment.
Display malfunctions can be caused by circuit
failures in four main areas. These are:
a.
The power supply.
b.
The light-emitting diode display (DS1).
c.
The associated display drive transistors (Q1-Q14).
d.
The logic in the hybrid ( U1).
7-16. Power Supply Verification. The power supply tests
in Paragraph 7-10 should be performed to verify that the
power supplies are functioning properly. Malfunctions in
the power supply can result in improper bias of Q 1 - Q14
resulting in a defective display.
7-17. Display Verification. A quick check will determine if
Model 3476A
any segments of the LED display (DSO are defective. The
following procedure should be used:
a.
Momentarily connect the emitter of Q2 through Q6
to the - 4 V test point.
b.
Verify that the display is completely illuminated as
illustrated in Figure 7-1.
c.
If this display is realized, the display is working
properly. When the display does not indicate properly, pro-
ceed with the next paragraph.
I II II II II I
I. II. II. II. II. I
Figure 7-1. Display Verification.
7-18. Display
Driver Verification and Troubleshooting.
The display drivers are divided into two groups: the digit
drivers Q2 - Q6 and the segment drivers Q7 - Q14. There-
fore, the first step in troubleshooting the display drivers is
to determine if the problem is segment related or digit re-
lated. During normal operation if the same segment in all
five sections is either "ON" or "OFF" continuously, the
associated segment driver and logic should be checked. If
one entire digit is either "ON" or "OFF" continuously, the
associated digit driver and logic should be checked. A
shorted QI will cause the entire display to turn "ON":
7-19. Display Logic Problems. The digital information that
controls the display is provided by NMOS Hybrid Ul which
is not field replaceable. If the Multimeter failure appears to
be traceable to Ul, refer to Paragraph 7-22 for Al PC
assembly replacement instructions.
7-20. SCHEMATIC DIAGRAMS.
7-21. Figures 7-2 and 7-3 are schematic diagrams of the
Multimeter and its power supply.
7-22. PRINTED
CIRCUIT
ASSEMBLY
EXCHANGE.
7-23. To provide maximum instrument performance for
minimum cost, the Multimeter is designed around an NMOS
Hybrid Integrated Circuit ( U1). This Hybrid and its associ-
ated discrete electronic circuitry are repairable only at the
Hewlett-Packard
Manufacturing
Division
using
special
equipment. An exchange program has been established to
permit field repair of the Multimeter by replacing the
entire Al printed circuit assembly with a factory rebuilt
assembly (-hp- Part No. 03476-69510). This assembly is
warranted to be fully operational and meet all instrument
specifications. For ordering details, contact the Hewlett-
Packard Sales and Service Office nearest you.
7-1
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