Circuitry; A/D Converter And - HP 3478A Technical Manual

3478A
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.
operation of the instrument.
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.
A/D CONVERTER AND LOGIC TROUBLESHOOTING
Service Group D Contents
Title
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
Its purpose is to control the
The Floating Common
SERVICE GROUP D
The instrument contains CMOS Integrated Circuits
which are extremely susceptible to failures due to
static discharge.
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.
Logic Circuitry, check and do the following:
a. Check the + 5V Power Supply and make sure it is
good. The supply should be between + 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
Paragraph
It is especially important that
Before troubleshooting the Chassis Common
TM 11-6625-3071-14