Troubleshooting; Introduction; 3478A Self-Test; Service Group Selection - HP 3478A Technical Manual

3 478A
a. Main Power Fuse. To replace the main power
fuse, first remove power from the 3478A.
flatblade screwdriver rotate the fuse terminal (at the rear
panel) counterclockwise. Remove the fuse and reinstall
with a replacement (refer to this manual's Section II or
Table 5-3 for the correct value). Reinstall the terminal.
b. Amps Fuse. The Amps Fuse is located inside
the 3478A's A (Amps) terminal (on the front panel). To
replace the fuse, first remove any cables connected to
the A terminal and then turn the instrument off. Use the
side slots on the A terminal to rotate the terminal
counterclockwise. The terminal and fuse will then
protrude from the front panel. Remove the terminal and
fuse, and replace the fuse with a 3A at 250V fast blow
fuse (-hp- Part No. 2110-0003). Return the terminal and
fuse to the front panel.

7-15. TROUBLESHOOTING

CAUTION
The instrument
Integrated Circuits which are susceptible
to failure due to static discharge. It is
especially important that grounded tools
and wrist straps be used when handling
or troubleshooting these components.

7-16 . Introduction

7-17. The following paragraphs and Service Groups
have troubleshooting information and procedures for the
-hp- Model 3478A
troubleshooting and repairing the 3478A, make sure the
failure is in the instrument rather than from any external
connections. Also make sure the instrument is
calibrated.

7-18. 3478A Self-Test

7-19. The 3478A Self-Test is designed to make sure
that most of the instrument's internal logic circuitry is
operational. The test is selected when the 3478A is first
turned on or by pressing the blue Shift button and then
the SGL/TRIG (TEST/RESET) button.
paragraphs have the Self-Test Failures and some
troubleshooting information.
7-20. U501 RAM Falls (U.C. RAM FAIL). This test
shows that the Chassis Common CPU's (Main Controller
U501) RAM has failed its internal self test. The failure is
normally caused by a defective U501. To make sure
U501 is the cause, go to Service Group D, paragraph 7-
D-21, for further troubleshooting.
contains CMOS
Digital Multimeter.
The following
7-21. Control ROM Fails (U.C. ROM FAIL).
indicates that the 3478A has failed its internal ROM self
With a
test. The Control ROM (U502) is the most likely cause.
Go to Service Group D, paragraph 7-D-19, for further
troubleshooting.
7-22. Calibration RAM Fails (CAL RAM FAIL). If this
test fails, an attempt made to calibrate the RAM was
unsuccessful. Go to Service Group D, paragraph 7-D-23
(Calibration Ram Failure) to check the CMOS RAM.
NOTE
The CAL ENABLE Switch on the front panel
should not be in the CAL/ENABLE position
under normal use. It should only be in that
position to calibrate or troubleshoot the
instrument.
7-23.
Calibrate the 3478A.
7-24. A/D Link Fails (A:D LINK FAIL).
shows that the Chassis Common Processor (Main
Controller, U501) is unable to communicate with the
Floating Common Processor (A/D Controller, U462). Go
to Service Group D, paragraph 7-D-44 (Isolation Circuitry
Troubleshooting) for troubleshooting.
7-25. A/D Slope Error (A:D SLOPE ERR). If the A/D
Converter is unable to do a proper conversion, this test
fails. Go to Service Group D, paragraph 7-D-35 (A/D
Converter Troubleshooting) for troubleshooting.
7-26. A/D Test Fails (A:D TEST FAIL). This shows that
the A/D Converter has failed its internal self test. Go to
Before
Service Group D, paragraph 7-D-35 (A/D Converter
Troubleshooting) for troubleshooting.

7-27. Service Group Selection

Service
Group
A
B
C
D
E
F
G
7-28. The Service Groups have the Troubleshooting
Information, Theory of Operation, and Schematics for the
3478A. Service Group F has the Theory of Operation
and Service Group G has the Schematics. The rest of
the groups have troubleshooting information.
7-2
Uncalibrated Instrument (UNCALIBRATED).
Table 7-1. 3478A Service Groups
Title
DC Volts and DC Current Troubleshooting
AC Volts and AC Current Troubleshooting
Ohms Troubleshooting
A/D Converter and Logic Troubleshooting
Power Supplies and Reference Troubleshooting
Theory of Operation
Schematics
TM 11-6625-3071-14
This
The failure