HP 3478A, Technical Manual

Page: 85 / 150

TM 11-6625-3071-14
3478A
SERVICE GROUP D
A/D CONVERTER AND LOGIC TROUBLESHOOTING
Service Group D Contents
Title Paragraph
Introduction ............................................................ 7-D-1
Chassis Common Logic Troubleshooting and
Failures............................................................ 7-D-5
Pre-Troubleshooting Information ........................ 7-D-7
Turn-On Failure...................................................... 7-D-9
Inoperative Display ........................................... 7-D-13
Inoperative Keyboard........................................ 7-D-15
HP-IB Failure .................................................... 7-D-17
U.C. ROM Fails................................................ 7-D-19
U.C. RAM Fails ................................................ 7-D-21
Calibration RAM Failure.................................... 7-D-23
Voltmeter Complete .......................................... 7-D-25
Address Switch Failure ..................................... 7-D-27
External Trigger ................................................ 7-D-29
Floating Common Logic Failures ......................... 7-D-31
Pre-Troubleshooting Information ...................... 7-D-33
A/D Converter Failures and Troubleshooting ... 7-D-35
Input Hybrid (U102) Inoperative........................ 7-D-40
A/D Controller Troubleshooting ........................ 7-D-42
Isolation Circuitry Troubleshooting....................... 7-D-44
7-D-1. INTRODUCTION
7-D-2. This Service Group has the A/D Converter and
Logic Circuitry troubleshooting information for the 3478A.
Unless otherwise specified, refer to Schematic 1 when
using the troubleshooting procedures.
7-D-3. The 3478A Logic Circuitry can be separated into
two major circuitry: Chassis Common Logic Circuitry and
Floating Common Logic Circuitry. The Chassis Common
Logic Circuitry consists of the Main Con- troller (US01),
Control ROM (U502), Calibration RAM (CMOS RAM,
U512), HP-IB Chip (U503), Display, Keyboard, and
associated circuitry. Its purpose is to control the
operation of the instrument. The Floating Common
Logic Circuitry consists of an A/D Controller (U462), A/D
Converter (U403, U401, etc.), and associated circuitry.
Its purpose is to control the A/D conversion, and to
control the Input Hybrid. Com- munications between the
circuitry are done by the Isola- tion Circuitry
7-D-4. Most of the procedures in this Service Group re-
quire a Signature Analyzer for troubleshooting. In addi-
tion to it, a logic probe and a logic pulser are also re-
quired for some troubleshooting procedures. Obtain the
required equipment, before going to the procedures.
The instrument contains CMOS Integrated Circuits
which are extremely susceptible to failures due to
static discharge. It is especially important that
grounded tools and wrist straps be used when
handling or troubleshooting these components.
7-D-5. CHASSIS COMMON LOGIC
TROUBLESHOOTING AND FAILURES
7-D-. The following paragraphs have the Chassis
Common Logic Failures and Troubleshooting.
7-D-7. Pro-Troubleshooting Information
7-D-8. Before troubleshooting the Chassis Common
Logic Circuitry, check and do the following:
a. Check the + 5V Power Supply and make sure it is
good. The supply should be b 4.9V and + 5.1
V. If the supply is inoperative, go to Service Group E for
troubleshooting.
b. Make sure the ALE line at U501 pin 11 is good, as
shown in Figure 7-D-1. If the signal is missing or wrong,
7-D-1