Agilent Technologies 6023A, 6028A User Manual

SERVICE MANUAL

AUTORANGING

DC POWER SUPPLY

AGILENT MODELS

6023A and 6028A

Agilent Part No. 5964-8283

FOR INSTRUMENTS WITH SERIAL NUMBERS

Agilent Model 6023A; Serials US36490101 and above
Agilent Model 6028A; Serials US36520101 and above

For instruments with higher serial numbers, a change page may be included.

Microfiche Part No. 5964-8284 Printed in USA: July 2001

CERTIFICATION

Agilent Technologies certifies that this product met its published specifications at time of shipment from the factory. Agilent
Technologies further certifies that its calibration measurements are traceable to the United States National Institute of
Standards and Technology, to the extent allowed by the Institute’s calibration facility, and to the calibration facilities of
other International Standards Organization members.

WARRANTY

This Agilent Technologies hardware product is warranted against defects in material and workmanship for a period of three
years from date of delivery. Agilent Technologies software and firmware products, which are designated by Agilent
Technologies for use with a hardware product and when properly installed on that hardware product, are warranted not to
fail to execute their programming instructions due to defects in material and workmanship for a period of 90 days from date
of delivery. During the warranty period Agilent Technologies will, at its option, either repair or replace products which
prove to be defective. Agilent Technologies does not warrant that the operation of the software, firmware, or hardware shall
be uninterrupted or error free.

For warranty service, with the exception of warranty options, this product must be returned to a service facility designated
by Agilent. Technologies. Customer shall prepay shipping charges by (and shall pay all duty and taxes) for products
returned to Agilent Technologies. for warranty service. Except for products returned to Customer from another country,
Agilent Technologies s hall p a y for return of products to Customer.

Warranty services outside the country of initial purchase are included in Agilent Technologies’ product price, only if
Customer pays Agilent Technologies international prices (defined as destination local currency price, or U.S. or Geneva
Export price).

If Agilent Technologies is unable, within a reasonable time to repair or replace any product to condition as warranted, the
Customer shall be entitled to a refund of the purchase price upon return of the product to Agilent Technologies.

LIMITATION OF WARRANTY

The foregoing warranty shall not apply to defects resulting from improper or inadequate maintenance by the Customer,
Customer-supplied software or interfacing, unauthorized modification or misuse, operation outside of the environmental
specifications for the product, or improper site preparation and maintenance. NO OTHER WARRANTY IS EXPRESSED
OR IMPLIED. AGILENT TECHNOLOGIES SPECIFICALLY DISCLAIMS THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.

EXCLUSIVE REMEDIES

THE REMEDIES PROVIDED HEREIN ARE THE CUSTOMER’S SOLE AND EXCLUSIVE REMEDIES. AGILENT
TECHNOLOGIES SHALL NOT BE LIABLE FOR ANY DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR
CONSEQUENTIAL DAMAGES, WHETHER BASED ON CONTRACT, TORT, OR ANY OTHER LEGAL THEORY.

ASSISTANCE

The above statements apply only to the standard product warranty. Warranty options, extended support contracts, product
maintenance agreements and customer assistance agreements are also available. Contact your nearest Agilent
Technologies Sales and Service office for further information on Agilent Technologies’ full line of Support Programs.

2

SAFETY SUMMARY

The following general safety precautions must be observed during all phases of operation, service and repair of this
instrument. Failure to comply with these precautions or with specific warnings elsewhere in this manual violates safety
standards of design, manufacture, and intended use of the instrument. Agilent Technologies, Inc. assumes no liability for the
customer's failure to comply with these requirements.

BEFORE APPLYING POWER.

Verify that the product is set to match the available line voltage and the correct fuse is installed.

GROUND THE INSTRUMENT.

This product is a Safety Class 1 instrument (provided with a protective earth terminal). To minimize shock hazard, the instrument chassis
and cabinet must be connected to an electrical ground. The instrument must be connected to the ac power supply mains through a three­conductor power cable, with the third wire firmly connected to an electrical ground (safety ground) at the power outlet. For instruments
designed to be hard wired to the ac power lines (supply mains), connect the protective earth terminal to a protective conductor before any
other connection is made. Any interruption of the protective (grounding) conductor or disconnection of the protective earth terminal will
cause a potential shock hazard that could result in personal injury. If the instrument is to be energized via an external autotransformer for
voltage reduction, be certain that the autotransformer common terminal is connected to the neutral (earth pole) of the ac power lines
(supply mains).

INPUT POWER MUST BE SWITCH CONNECTED.

For instruments without a built-in line switch, the input power lines must contain a switch or another adequate means for disconnecting
the instrument from the ac power lines (supply mains).

DO NOT OPERATE IN AN EXPLOSIVE ATMOSPHERE.

Do not operate the instrument in the presence of flammable gases or fumes.

KEEP AWAY FROM LIVE CIRCUITS.

Operating personnel must not remove instrument covers. Component replacement and internal adjustments must be made by qualified
service personnel. Do not replace components with power cable connected. Under certain conditions, dangerous voltages may exist even
with the power cable removed. To avoid injuries, always disconnect power, discharge circuits and remove external voltage sources before
touching components.

DO NOT SERVICE OR ADJUST ALONE.

Do not attempt internal service or adjustment unless another person, capable of rendering first aid and resuscitation, is present.

DO NOT EXCEED INPUT RATINGS.

This instrument may be equipped with a line filter to reduce electromagnetic interference and must be connected to a properly grounded
receptacle to minimize electric shock hazard. Operation at the line voltage or frequencies in excess of those stated on the data plate may
cause leakage currents in excess of 5.0mA peak.

SAFETY SYMBOLS.

DO NOT SUBSTITUTE PARTS OR MODIFY INSTRUMENT.

Because of the danger of introducing additional hazards, do not install substitute parts or perform any unauthorized modification to the
instrument. Return the instrument to a Agilent Technologies, Inc. Sales and Service Office for service and repair to ensure that safety
features are maintained.

Instruction manual symbol: the product will be marked with this symbol when it is necessary for the user to refer to the
instruction manual (refer to Table of Contents) .

Indicates hazardous voltages.

Indicate earth (ground) terminal.

The WARNING sign denotes a hazard. It calls attention to a procedure, practice, or the like, which, if not correctly
performed or adhered to, could result in personal injury. Do not proceed beyond a WARNING sign until the indicated
conditions are fully understood and met.

The CAUTION sign denotes a hazard. It calls attention to an operating procedure, or the like, which, if not correctly
performed or adhered to, could result in damage to or destruction of part or all of the product. Do not proceed beyond
a CAUTION sign until the indicated conditions are fully understood and met.

Instruments which appear damaged or defective should be made inoperative and secured against unintended operation until they can be
repaired by qualified service personnel.

3

SAFETY SYMBOL DEFINITIONS

Symbol Description Symbol Description

Direct current Terminal for Line conductor on permanently

installed equipment

Alternating current Caution, risk of electric shock

Both direct and alternating current Caution, hot surface

Three-phase alternating current Caution (refer to accompanying documents)

Earth (ground) terminal In position of a bi-stable push control

Protective earth (ground) terminal Out position of a bi-stable push control

Frame or chassis terminal On (supply)

Terminal for Neutral conductor on
permanently installed equipment

Terminal is at earth potential
(Used for measurement and control
circuits designed to be operated with
one terminal at earth potential.)

Printing History

The edition and current revision of this manual are indicated below. Reprints of this manual containing minor corrections

and updates may have the same printing date. Revised editions are identified by a new printing date. A revised edition
incorporates all new or corrected material since the previous printing date. Changes to the manual occurring between
revisions are covered by change sheets shipped with the manual. Also, if the serial number prefix of your power supply is
higher than those listed on the title page of this manual, then it may or may not include a change sheet. That is because
even though the higher serial number prefix indicates a design change, the change may not affect the content of the manual.

Edition 1 July, 2001

© Copyright 2001 Agilent Technologies, Inc.

This document contains proprietary information protected by copyright. All rights are reserved. No part of this document

may be photocopied, reproduced, or translated into another language without the prior consent of Agilent Technologies,
Inc. The information contained in this document is subject to change without notice.

Off (supply)

Standby (supply)
Units with this symbol are not completely
disconnected from ac mains when this switch is
off. To completely disconnect the unit from ac
mains, either disconnect the power cord or have
a qualified electrician install an external switch.

4

TABLE OF CONTENTS

Introduction ............................................................................................................................................................................7

Scope ....................................................................................................................................................................................7

Calibration and Verification .............................................................................................................................................7

Troubleshooting................................................................................................................................................................7

Principles of Operation ..................................................................................................................................................... 7

Replaceable Parts.............................................................................................................................................................. 7

Circuit Diagrams............................................................................................................................................................... 7

Safety Considerations ........................................................................................................................................................... 7

Manual Revisions .................................................................................................................................................................8

Calibration and Verification.................................................................................................................................................. 9

Introduction...........................................................................................................................................................................9

Test Equipment Required ..................................................................................................................................................... 9

Operation Verification Tests................................................................................................................................................. 9

Calibration Procedure ........................................................................................................................................................... 9

Initial Setup..................................................................................................................................................................... 11

Performance Tests ..............................................................................................................................................................14

Measurement Techniques ...............................................................................................................................................14

Constant Voltage (CV) Tests..........................................................................................................................................15

Constant Current (CC) Tests...........................................................................................................................................21

Troubleshooting .................................................................................................................................................................... 23

Introduction.........................................................................................................................................................................23

Initial Troubleshooting Procedures..................................................................................................................................... 23

Electrostatic Protection....................................................................................................................................................... 25

Repair and Replacement ..................................................................................................................................................... 25

A2 Control Board Removal............................................................................................................................................ 26

A4 Power Mesh Board Removal .................................................................................................................................... 27

A3 Front-Panel Board Removal......................................................................................................................................27

A1 Main Board Removal................................................................................................................................................ 27

Overall Troubleshooting Procedure.................................................................................................................................... 27

Using the Tables ............................................................................................................................................................. 28

Main Troubleshooting Setup ..........................................................................................................................................29

Troubleshooting No-Output Failures.............................................................................................................................. 31

Front-Panel Troubleshooting .......................................................................................................................................... 31

Troubleshooting Bias Supplies ....................................................................................................................................... 33

Power Section Blocks ..................................................................................................................................................... 35

Troubleshooting AC-Turn-on Circuits............................................................................................................................35

Troubleshooting PWM & Clock..................................................................................................................................... 36

Troubleshooting DC-To-DC Converter.......................................................................................................................... 37

Troubleshooting CV Circuit ...........................................................................................................................................38

Troubleshooting CC Circuit............................................................................................................................................38

Troubleshooting Down Programmer ..............................................................................................................................39

Troubleshooting OVP Circuit.........................................................................................................................................39

Principles of Operation ........................................................................................................................................................43

Autoranging Power.............................................................................................................................................................43

Block Diagram Overview ................................................................................................................................................... 43

Simplified Schematic...................................................................................................................................................... 45

DC-to-DC Converter.......................................................................................................................................................47

Down Programmer..........................................................................................................................................................47

Constant-Voltage (CV) Circuit.......................................................................................................................................48

Constant-Current (CC) Circuit........................................................................................................................................49

5

Overvoltage Protection (OVP) Circuit............................................................................................................................49

Power-Limit Comparator................................................................................................................................................ 49

Control-Voltage Comparator .......................................................................................................................................... 49

Initial-Ramp Circuit........................................................................................................................................................ 50

Pulse-Width Modulator (PWM) .....................................................................................................................................50

Bias Voltage Detector.....................................................................................................................................................50

AC-Surge Dropout Detector ........................................................................................................................................... 50

1-Second-Delay Circuit .................................................................................................................................................. 51

Display Circuits .................................................................................................................................................................. 51

Replaceable Parts..................................................................................................................................................................53

Introduction.........................................................................................................................................................................53

Ordering Information.......................................................................................................................................................... 54

Component Location and Circuit Diagrams ...................................................................................................................... 69

System Option 002 ................................................................................................................................................................ 79

General Information............................................................................................................................................................ 79

Specifications.................................................................................................................................................................. 79

Option 002 Hardware......................................................................................................................................................79

Installation .......................................................................................................................................................................... 83

Connector Assembly Procedure......................................................................................................................................83

Operation ............................................................................................................................................................................ 84

Local/Remote Programming........................................................................................................................................... 85

Remote Resistance Programming................................................................................................................................... 87

Remote Monitoring......................................................................................................................................................... 89

Status Indicators..............................................................................................................................................................90

Remote Control...............................................................................................................................................................90

Power-On Preset ................................................................................................................................................................. 92

AC Dropout Buffer Circuit.............................................................................................................................................93

Multiple Supply System Shutdown ................................................................................................................................93

Bias Supplies ..................................................................................................................................................................94

Maintenance........................................................................................................................................................................ 94

Troubleshooting..............................................................................................................................................................95

Troubleshooting Resistance and Voltage Programming.................................................................................................95

Troubleshooting Current Programming.......................................................................................................................... 95

Backdating........................................................................................................................................................................... 107

6

1

Introduction

Scope

This manual contains information for troubleshooting the Agilent 6023A or 6028A 200W Autoranging Power Supply to the
component level. Wherever applicable, the service instructions given in this manual refer to pertinent information provided
in the Operation Manual. Both manuals cover Agilent Models 6023A/28A; differences between models are described as
required.

The following information is contained in this manual.

Calibration and Verification

Contains calibration procedures for Agilent Models 6023A/28A. Also contains verification procedures that check the
operation of the supplies to ensure they meet the specifications of Chapter 1 in the Operating Manual.

Troubleshooting

Contains troubleshooting procedures to isolate a malfunction to a defective component on the main circuit board or to a
defective assembly (front-panel, power transformer, or cable assembly). Board and assembly level removal and
replacement procedures are also given in this section.

Principles of Operation

Provides block diagram level descriptions of the supply's circuits. The regulation & control, protection, input power, dc
power conversion and output circuits are described. These descriptions are intended as an aid in troubleshooting.

Replaceable Parts

Provides a listing of replaceable parts for all electronic components and mechanical assemblies for Agilent Models
6023A/28A.

Circuit Diagrams

Contains functional schematics and component location diagrams for all Agilent 6023A/28A circuits. The names that
appear on the functional schematics also appear on the block diagrams in Chapter 4. Thus, the descriptions in Chapter 4 can
be correlated with both the block diagrams and the schematics.

Safety Considerations

This product is a Safety Class 1 instrument, which means that it is provided with a protective earth terminal. Refer to the
Safety Summary page at the beginning of this manual for a summary of general safety information. Safety information for
specific procedures is located at appropriate places in the manual.

7

Manual Revisions

Agilent Technologies instruments are identified by a 10-digit serial number. The format is described as follows: first two
letters indicate the country of manufacture. The next four digits are a code that identify either the date of manufacture or of
a significant design change. The last four digits are a sequential number assigned to each instrument.

Item Description

US The first two letters indicates the country of manufacture, where US = USA; MY = Malaysia.

3648 This is a code that identifies either the date of manufacture or the date of a significant design change.

0101 The last four digits are a unique number assigned to each power supply.

If the serial number prefix on your unit differs from that shown on the title page of this manual, a yellow Manual Change
sheet may be supplied with the manual. It defines the differences between your unit and the unit described in this manual.
The yellow change sheet may also contain information for correcting errors in the manual.

Note that because not all changes to the product require changes to the manual, there may be no update information
required for your version of the supply.

Older serial number formats used with these instruments had a two-part serial number, i.e. 2701A-00101. This manual also
applies to instruments with these older serial number formats. Refer to Appendix B for backdating information.

8

2

Calibration and Verification

Introduction

This section provides test and calibration procedures. The operation-verification tests comprise a short procedure to verify
that the unit is performing properly, without testing all specified parameters. After troubleshooting and repair of a defective
power supply you can usually verify proper operation with the turn-on checkout procedure in the Operating Manual.
Repairs to the A1 main board and the A2 control board can involve circuits which, although functional, may prevent the
unit from performing within specified limits. So, after A1 or A2 board repair, decide if recalibration and operation
verification tests are needed according to the faults you discover. Use the calibration procedure both to check repairs and
for regular maintenance.

When verifying the performance of this instrument as described in this chapter, check only those specifications for which a
performance test procedure is included.

Test Equipment Required

Table 2-1 lists the equipment required to perform the tests of this section. You can separately identify the equipment for
performance tests, calibration and troubleshooting using the USE column of the table.

Operation Verification Tests

To assure that the unit is performing properly, without testing all specified parameters, first perform the turn-on checkout
procedure in the Operating Manual. Then perform the following performance tests, in this section.

CV Load Effect
CC Load Effect

Calibration Procedure

Calibrate the unit twice per year and when required during repair. The following calibration procedures which follow
should be performed in the sequence given. Table 2-2 describes in detail these calibration procedures and lists the expected
results to which each adjustment must be made.

Note: Some of the calibration procedures for this instrument can be performed independently, and some

procedures must be performed together and/or in a prescribed order. If a procedure contains no references
to other procedures, you may assume that it can be performed independently.

To return a serviced unit to specifications as quickly as possible with minimal calibration, the technician
need only perform calibration procedures that affect the repaired circuit. Table 2-3 lists various power
supply circuits with calibration procedures that should be performed after those circuits are serviced.

9

Table 2-1. Test Equipment Required

TYPE REQUIRED CHARACTERISTICS USE RECOMMENDED MODEL

Oscilloscope Sensitivity: 1 mV

Bandwidth: 20MHz & 100MHz
Input: differential, 50Ω & 10MΩ

P,T Agilent 1740A

RMS Voltmeter True rms, 10MHz bandwidth

P Agilent 3400B
Sensitivity: 1 mV
Accuracy: 5%

Logic Pulser 4.5 to 5.5Vdc @ 35mA T Agilent 546A

Multimeter Resolution: 100nV

P,A,T Agilent 3458A
Accuracy: 0.0035%, 6½ digit

CC PARD Test
Current Probe

No saturation at 30Adc
Bandwidth: 20Hz to 20MHz

P Tektronix P6303

Probe/AM503 Amp/
TM500 Power Module

Electronic Load* Voltage range: 60Vdc

P,A Agilent 6060B
Current range: 60Adc
Power range: 300 watts
Open and short switches

CC PARD Test & I
Cal Resistive Load*

Value: 0.25 ohms >250W

P

Accuracy: 1%

P,A

Rheostat or Resistor Bank

Current-Monitoring
Resistors

6023A
Value: 30mV @ 30A (1mΩ )

P,A

Accuracy: 1%
TC: 30ppm/°C

Value: 30mV @ 30A (1mΩ)

Accuracy: 0.05% **

TC: 30ppm/°C (A,P)
6028A
Value 100MΩ ± 0.04% @ 25W

Guidline 9230/15

Accuracy: 1%

PC: 0.0004% 1W

Calibration and Test
Resistors

Terminating
Resistors (4)

Blocking
Capacitors (2)
Common-mode
Toroidal Core

10

Value: 100Ω, 5%, 1W

1Ω, 5%, 1/2W

1KΩ, 5% 1/4W

5KΩ, 5% 1/4W (6023A)

2KΩ, 0.01% 1/4W

Value: 50Ω ±5%, noninductive

Value: 0.01µF, 100Vdc

A,T

P

P

P Ferrox-Cube

500T600-3C8,
Agilent 9170-0061

Table 2-1. Test Equipment Required (continued)

TYPE REQUIRED CHARACTERISTICS USE RECOMMENDED MODEL

Switch SPST, 30A @ 20V P
DC Power Supply Voltage range: 0-60Vdc

Current range: 0-3Adc

T,P Agilent 6296A

Variable Voltage
Transformer
(autotransformer)

P = performance testing A = calibration adjustments T = troubleshooting

* Resistors may be substituted for test where an electronic load is not available.
** Less accurate, and less expensive, current-monitor resistors can be used, but the accuracy to which current programming

and current meter reading can be checked must be reduced accordingly.

Range greater than -13% to +6% of
nominal input AC voltage
1KVA

P,A

Initial Setup

Maintenance described herein is performed with power supplied to the instrument, and protective covers

removed. Such maintenance should be performed only by service trained
personnel who are aware of the hazards involved (for example, fire and electrical shock).
Turn off ac power when making or removing connections to the power supply. Where
maintenance can be performed without power applied, the power should be
removed.

a. Unplug the line cable and remove the top cover by removing three screws; the rear handle screw and the two top-rear

corner screws. Do not remove the front handle screw as the retaining nut will fall into the unit.

b. Slide the cover to the rear.
c. Plug a control board test connector A2P3 onto the A2J3 card-edge fingers.
d. Turn OVERVOLTAGE ADJUST control A3R59 fully clockwise.
e. Disconnect all loads from output terminals.
f. Connect power supply for local sensing, and ensure that MODE switches are set as shown below.

g. Reconnect the line cable and turn on ac power.
h. Allow unit to warm up for 30 minutes.
i. When attaching the DVM, the minus lead of the DVM should be connected to the first node listed, and the plus lead

should be connected to the second node listed.

j. At the beginning of each calibration procedure, the power supply should be in its power-off state, with no external

circuitry connected except as instructed.

k. The POWER LIMIT adjustment (A2R25) must be adjusted at least coarsely before many of the calibration procedures

can be performed. If you have no reason to suspect that the Power Limit circuit is out of adjustment, and you do not
intend to recalibrate it, do not disturb its setting. Otherwise, center A2R25 before you begin to calibrate the power
supply.

l. To disable the power supply, short INHIBIT line A2J3 pin 8 to COMMON A2J3 pin 4.

11

Table 2-2. Calibration Procedure

TEST TESTED

VARIABLE

Meter F/S
Adjust.

Resistance
Programming
F/S
Adjust.

V-MON
Zero
Adjust.

Common
Mode
Adjust.

I-MON
Zero
Adjust.

I-MON
F / S
Adjust.

*IR = Initial Reading

Meter Ref.
Voltage

Prog. Voltage VP ( + )

V-MON VM ( + )

Residual
Output
Voltage
VM( + )

I-MON IM ( + )

I-MON IM ( + )

TEST POINTS TEST SEQUENCE AND ADJUSTMENTS EXPECTED

RESULTS

A2J3 pin 6 ( + )

M ( - )

P ( - )

M ( - )

VM ( + )

M ( - )

M (-)

M ( - )

Rm ( + )
Rm ( - )

a. Connect DVM across test points and turn on

ac power.

b. Adjust A2R24 to obtain the voltage range

specified in the results.

a. Connect a 2KΩ 0.01%, ¼W programming

resistor and DVM between test points.

b. Set MODE switch as in Figure 2-1 and turn on

ac power.

c. Adjust A2R23 to obtain the voltage range

specified in the results.

a. Set voltage and current controls to minimum

settings.

b. Disable power supply as in Initial Setup step i.
c. Short circuit output terminals and connect the

DVM between test points. Turn on power
supply.

d. Adjust V-MON Zero trim pot A2R22 to

voltage range specified in the results.

a. Set voltage and current controls to minimum.
b. Disable power supply as Initial Setup step i.
c. Turn on ac power and record the initial

voltage (IR) with DVM across test points.

d. Remove the - S( + ) and – OUT( - ) and

connect a 1Vdc power supply between - S( + )
and – OUT( - ). See Figure 2-1.

e. Adjust A2R21 to the voltage range specified.
f. Remove the 1V supply and replace jumpers.
a. Set voltage and current controls to minimum.
b. Turn on ac power.
c. Connect DVM across test points and adjust

I-MON Zero trim pot A2R8 as shown in
results.

a. Perform I-MON Zero Adjust before

proceeding .

b. Connect a 0.001Ω 0.05% (6023A), 0.100Ω

0.05% (6028A) current monitoring resistor
Rm across the output terminals.

c. Turn on ac power and using the “Display

Setting”, set current control to 30A (6023A),
10A (6028A), and voltage control to 5V.

d. Connect DVM across test points and take an

initial reading (IR).

e. Connect DVM across Rm monitoring

terminals and adjust A2R9 as shown in the
results.

0.5V ± 50µV

2.5V ±4mV

0 ± 20µV

IR ± 20µV

0 ± 100µV
(6023A)
0 ± 25µV
(6028A)

IR*

0.006 IR*
+40µV (6023A),

0.200 ± 1µV
(6028A)

12

Table 2-2. Calibration Procedure (continued)

TEST TESTED

VARIABLE

Power
Limit
Adjust.

V(OUT)
I(OUT)

TEST POINTS TEST SEQUENCE AND ADJUSTMENTS EXPECTED

RESULTS

a. Perform I-MON F/S Adjust before

proceeding.

b. Connect the unit to the ac power line via the

external variable auto-transformer which is set
to nominal line voltage.

c. Connect a 0.25Ω, 250W (6023A), 2.3Ω,

250W (6028A) resistor across the unit's output
and turn on ac power.

d. Set voltage control to 9V (6023A) 9V≥ 3V

(6028A) and current control to 30.2A
(6023A), 10.2A (6028A)

e. Set auto-transformer to minimum line

voltage.

f. Turn A2R25 fully counterclockwise.
g. Slowly adjust A2R25 clockwise until CC

LED just lights.

30.2A 7.55V for
CC operation
(6023A)

10.2A, 23V for
CC operation
(6028A)

Figure 2-1. Common Mode Setup

13

Table 2-3. Guide to Recalibration After Repair

Printed Circuit

Board

A1 Main Board R3 4
A1 Main Board T1 4 then 5
A4 Power Mesh T3 4 then 5 Board
A4 Power Mesh CR7 4 then 5 Board
A2 Control Board Constant Voltage

A2 Control Board Constant Voltage

A2 Control Board Constant Current

A2 Control Board Power Limit

A2 Control Board Bias Power Supplies
A2 Control Board U9, R79, R80, R24 7

1. V-MON Zero Calibration

2. Common-Mode Calibration

3. I-MON Full Scale (F/S) Zero Calibration

Block Name Circuit Within

Block

All Except Current

(CV) Circuit

(CV) Circuit

(CC) Circuit

Comparator

* Code To Calibration Procedure To Be Performed

Source

Current Source All 6

± 15V Supplies

4. I-MON Full Scale (F/S) Calibration

5. Power Limit Calibration

6. Resistance Programming Full Scale (F/S) Calibration

7. Meter Full Scale (F/S) Calibration

Ref.

Designator

All 1 then 2

All 3 then 4

All 4 then 5

All All

Perform These

Procedures*

Performance Tests

The following paragraphs provide test procedures for verifying the unit's compliance with the specifications of Table 1-1 in
the Operating Manual. Please refer to CALIBRATION PROCEDURE or TROUBLESHOOTING if you observe
out-of-specification performance.

Measurement Techniques

Setup For All Tests. Measure the output voltage directly at the + S and - S terminals. Connect unit for local sensing, and
ensure that MODE switches are set as shown below. Select an adequate wire gauge for load leads using the procedures
given in the Operating Manual for connecting the load.

Electronic Load. The test and calibration procedures use an electronic load to test the unit quickly and accurately. If an
electronic load is not available, you may substitute a 2Ω 250W load resistor for the electronic load in these tests:

CV Source Effect (Line Regulation)
CC Load Effect (Load Regulation)

You may substitute a 0.25Ω 250W load resistor in these tests:

CV Load Effect (Load Regulation)
CV PARD (Ripple and Noise)
CC Source Effect (Line Regulation)
CC PARD (Ripple and Noise)

14

The substitution of the load resistor requires adding a load switch to open and short the load in the CC or CV load
regulation tests. The load transient recovery time test procedure cannot be performed using load resistors.

An electronic load is considerably easier to use than a load resistor. It eliminates the need for connecting resistors or
rheostats in parallel to handle the power, it is much more stable than a carbon-pile load, and it makes easy work of
switching between load conditions as is required for the load regulation and load transient-response tests.

Current-Monitoring Resistor Rm. To eliminate output current measurement error caused by voltage drops in the leads
and connections, connect the current-monitoring resistor between -OUT and the load as a four-terminal device. Figure 2-2
shows correct connections. Select a resistor with stable characteristics: 0.001, 1% accuracy, 30 ppm/°C or lower
temperature coefficient and 20W power rating (20 times actual power if other than 0.001Ω is used).

Figure 2-2. Current-Monitoring Resistor Setup

Constant Voltage (CV) Tests

CV Setup. If more than one meter or a meter and an oscilloscope are used, connect each to the + S and - S terminals by a
separate pair of leads to avoid mutual coupling effects. Connect only to + S and -S (except for peak-to-peak PARD)
because the unit regulates the output voltage between + S and - S, not between + OUT and - OUT. Use coaxial cable or
shielded 2-wire cable to avoid pickup on test leads. For all CV tests set the output current at full output to assure CV
operation.

Load Effect (Load Regulation). Constant-voltage load effect is the change in dc output voltage (Eo) resulting from a
load-resistance change from open-circuit to full-load. Full-load is the resistance which draws the maximum rated output
current at voltage Eo. Proceed as follows:
a. Connect the test equipment as shown in Figure 2-3. Operate the load in constant resistance mode (Amps/Volt) and set

resistance to maximum.

b. Turn the unit's power on, and turn up current setting to full output.
c. Turn up output voltage to:

7.0Vdc (6023A)

20.0Vdc (6028A)
as read on the digital voltmeter.

15

Figure 2-3. Basic Test Setup

d. Reduce the resistance of the load to draw an output current of:
29Adc (6023A)
10Adc (6028A)
Check that the unit's CV LED remains lighted.

e. Record the output voltage at the digital voltmeter.
f. Open-circuit the load.
g. When the reading settles, record the output voltage again. Check that the two recorded readings differ no more than:

± 0.0027Vdc (6023A)
± 0.0090Vdc (6028A)

Source Effect (Line Regulation). Source effect is the change in dc output voltage resulting from a change in ac input
voltage from the minimum to the maximum value as specified in Input Power Requirements in the Specifications Table, in
the Operating Manual. Proceed as follows:
a. Connect the test equipment as shown in Figure 2-3. Operate the load in constant resistance mode (Amps/Volt) and set

resistance to maximum.

b. Connect the unit to the ac power line through a variable autotransformer which is set for low line voltage (104Vac for

120Vac).

c. Turn the unit's power on, and turn up current setting to full output.
d. Turn up output voltage to:

20.0Vdc (6023A)
60Vdc (6028A)
as read on the digital voltmeter.

e. Reduce the resistance of the load to draw an output current of:

10Adc (0.010Vdc across Rm) (6023A)

3.3Adc(0.33Vdc across Rm) (6028A)
Check that the unit's CV LED remains lighted.

16

f. Record the output voltage at the digital voltmeter.
g. Adjust autotransformer to the maximum for your line voltage.
h. When the reading settles record the output voltage again. Check that the two recorded readings differ no more than:

± 0.0030Vdc (6023A)
± 0.0080Vdc (6028A)

PARD (Ripple And Noise). Periodic and random deviations (PARD) in the unit's output-ripple and noise-combine to
produce a residual ac voltage superimposed on the dc output voltage. Constant-voltage PARD is specified as the
root-mean-square (rms) or peak-to-peak (pp) output voltage in a frequency range of 20Hz to 20MHz.

RMS Measurement Procedure. Figure 2-4 shows the interconnections of equipment to measure PARD in Vrms. To
ensure that there is no voltage difference between the voltmeter's case and the unit's case, connect both to the same ac
power outlet or check that the two ac power outlets used have the same earth-ground connection.

Use the common-mode choke as shown to reduce ground-loop currents from interfering with measurement. Reduce noise
pickup on the test leads by using 50Ω coaxial cable, and wind it five turns through the magnetic core to form the
common-mode choke. Proceed as follows:
a. Connect the test equipment as shown in Figure 2-4. Operate the load in constant resistance mode (Amps/Volt) and set

resistance to maximum.

b. Turn the unit's power on, and turn up current setting to full output.
c. Turn up output voltage to:

7Vdc (6023A)
20Vdc (6028A)
d. Reduce the resistance of the load to draw an output current of:
29Adc (6023A)
10Adc (6028A)
Check that the unit's CV LED remains lighted.

e. Check that the rms noise voltage at the true rms voltmeter is no more than:

3.0mV rms (6023A)

3.0mV rms (6028A)

Figure 2-4. RMS Measurement Test Setup, CV PARD Test

Peak Measurement Procedure. Figure 2-5 shows the interconnections of equipment to measure PARD in Vpp. The
equipment grounding and power connection instructions of PARD rms test apply to this setup also. Connect the

oscilloscope to the + OUT and - OUT terminals through 0.01µF blocking capacitors to protect the oscilloscope's input from

17

the unit's output voltage. To reduce common-mode noise pickup, set up the oscilloscope for a differential, two-channel
voltage measurement. To reduce normal-mode noise pickup, use twisted, 1 meter or shorter, 50Ω coaxial cables with
shields connected to the oscilloscope case and to each other at the other ends. Proceed as follows:

a. Connect the test equipment as shown in Figure 2-5. Operate the load in constant resistance mode (Amps/Volt) and set

resistance to maximum.

b. Turn the unit's power on, and turn up current setting to full output.
c. Turn up output voltage to:

7.0Vdc (6023A)
20Vdc (6028A)
d. Reduce the resistance of the load to draw an output current of:

29.0Adc (6023A)
10Adc (6028A)
Check that the unit's CV LED remains lighted.

e. Set the oscilloscope's input impedance to 50Ω and bandwidth to 20MHz. Adjust the controls to show the 20KHz and

higher frequency output-noise waveform of Figure 2-6.

f. Check that the peak-to-peak is no more than 30mV.

18

Figure 2-5. Peak-To-Peak Measurement Test Setup, CV PARD Test

6023A 6028A

Figure 2-6. 20KHz Noise, CV Peak-to-Peak PARD

Load Transient Recovery Time. Specified for CV operation only; load transient recovery time is the time for the output
voltage to return to within a specified band around its set voltage following a step change in load.

Proceed as follows:

a. Connect the test equipment as shown in Figure 2-3. Operate the load in constant-current mode and set for minimum

current.

b. Turn the unit's power on, and turn up current setting to full output.
c. Turn up output voltage to:

6.70Vdc (6023A)

20.0Vdc (6028A)
as read on the digital voltmeter.
d. Set the load to vary the load current between:
27 and 30Adc (6023A)
9 and 10Adc (6028A)
at a 30Hz rate.

e. Set the oscilloscope for ac coupling, internal sync and lock on either the positive or negative load transient.
f. Adjust the oscilloscope to display transients as in Figure 2-7.
g. Check that the pulse width of the transient pulse is no more than:

50mV (6023A)
75mV (6028A)

19

Temperature Coefficient. (6023A) Temperature coefficient (TC) is the change in output voltage for each °C change in
ambient temperature with constant ac line voltage, constant output voltage setting and constant load resistance. Measure
temperature coefficient by placing the unit in an oven, varying the temperature over a range within the unit's operating
temperature range, and measuring the change in output voltage. Use a large, forced air oven for even temperature distribution.
Leave the unit at each temperature measurement for half hour to ensure stability in the measured variable. Measure the output
voltage with a stable DVM located outside the oven so voltmeter drift does not affect the measurement accuracy. To measure
offset TC, repeat the procedure with output voltage set to 0.10Vdc.
Proceed as follows:

a. Connect DVM between +S and -S.
b. Place power supply in oven, and set temperature to 30°C.
c. Turn the unit's power on and turn up current setting to full output.
d. Turn up output voltage to 20Vdc as read on the DVM.
e. After 30 minutes stabilization record the temperature to the nearest 0.1°C. Record the output voltage at the DVM.
f. Set oven temperature to 50°C.
g. After 30 minutes stabilization, record the temperature to the nearest 0.1°C. Record output voltage.
h. Check that the magnitude of the output voltage change is no greater than 32mV.

6023A 6028A

Figure 2-7. Load Transient Recovery Waveform

Drift (Stability) (6023A). Drift is the change in output voltage beginning after a 30-minute warm-up during 8 hours operation
with constant ac input line voltage, constant load resistance and constant ambient temperature. Use a DVM and record the
output at intervals, or use a strip-chart recorder to provide a continuous record. Check that the DVM's or recorder's specified
drift during the 8 hours will be no more than 0.001%. Place the unit in a location with constant air temperature preferably a
large forced-air oven set to 30°C and verify that the ambient temperature does not change by monitoring with a thermometer
near the unit. Typically the drift during 30 minute warm-up exceeds the drift during the 8-hour test. To measure offset drift,
repeat the procedure with output voltage set to 0.10Vdc.

a. Connect DVM between + S and - S.
b. Turn the unit's power on and turn up current setting to full output.
c. Turn up output voltage to 20Vdc as read on the digital voltmeter.
d. After a 30 minute warmup, note reading on DVM.
e. The output voltage should not deviate more than 5mV from the reading obtained in step d over a period of 8 hours.

20

Constant Current (CC) Tests

CC Setup. Constant-current tests are analogous to constant-voltage tests, with the unit's output short circuited and the
voltage set to full output to assure CC operation. Follow the general setup instructions.

Load Effect (Load Regulation). Constant current load effect is the change in dc output current (Io) resulting from a
load-resistance change from short-circuit to full-load, or full-load to short-circuit. Full-load is the resistance which develops
the maximum rated output voltage at current Io. Proceed as follows:

a. Connect the test equipment as shown in Figure 2-3. Operate the load in constant resistance mode (Amps/Volt) and set

resistance to minimum.

b. Turn the unit's power on, and turn up voltage setting to full output.
c. Turn up output current to:

10.0Adc (0.010Vdc across Rm) (6023A). Check that the AMPS display reads about 10 amps.

3.3Adc (0.335Vdc across Rm) (6028A) Check that the AMPS display reads about 3.3 amps.

d. Increase the load resistance until the output voltage at +S and -S increases to:

20Vdc (6023A).
60Vdc (6028A).
Check that the CC LED is lighted and AMPS display still reads ≈ current setting.

e. Record voltage across Rm.
f. Short circuit the load.
g. When the reading settles (≈ 10s), record the voltage across Rm again. Check that the two recorded readings differ no

more than:

± 0.010mVdc (6023A)
± 0.0053mVdc (6028A)

h. Disconnect the short across the load.

Source Effect (Line Regulation). Constant current source effect is the change in dc output current resulting from a
change in ac input voltage from the minimum to the maximum values listed in the Specifications Table in the Operating
Manual. Proceed as follows:
a. Connect the test equipment as shown in Figure 2-3. Operate the load in constant resistance mode (Amps/Volt) and set

resistance to minimum.

b. Connect the unit to the ac power line through a variable autotransformer set for low line voltage (e.g. 104Vac for

120Vac).

c. Switch the unit's power on and turn up output voltage setting to full output.
d. Turn up output current to:

29.0Adc (0.029Vdc across Rm) (6023A)

10.0Adc (1.0Vdc across Rm) (6028A)
Check that the AMPS display reads ≈ current setting.
e. Increase the load resistance until the output voltage between + S and - S increases to:

7.0Vdc (603A)

20.0Vdc (6028A)
Check that the CC LED is still on and the AMPS display still reads ≈ current setting.

f. Record the voltage across Rm.
g. Adjust autotransformer to the maximum for your line voltage.
h. When the reading settles record the voltage across Rm again. Check that the two recorded readings differ no more than:

± 0.0090mVdc (6023A)
± 0.030mVdc (6028A)

PARD Ripple And Noise. Periodic and random deviations (PARD) in the unit's output (ripple and noise) combine to
produce a residual ac current as well as an ac voltage super-imposed on the dc output. The ac voltage is measured as
constant-voltage PARD. Constant-current PARD is specified as the root-mean-square (rms) output current in a frequency
range 20Hz to 20MHz with the unit in CC operation. To avoid incorrect measurements, with the unit in CC operation,
caused by the impedance of the electronic load at noise frequencies, use a:

21

0.25Ω (6023A)

2.0Ω (6028A)

load resistor that is capable of safely dissipating 250 watts. Proceed as follows:
a. Connect the test equipment as shown in Figure 2-8.
b. Switch the unit's power on and turn the output voltage all the way up.
c. Turn up output current to:

29.0Vdc (6023A)
10Vdc (6028A)
Check that the unit's CC LED remains lighted.

d. Check that the rms noise current measured by the current probe and rms voltmeter is no more than:

15mA rms (6023A).
5mA rms (6028A)

Figure 2-8. CC PARD Test Setup

22

Troubleshooting

Maintenance described herein is performed with power supplied to the instrument, and protective covers

removed. Such maintenance should be performed only by service-trained personnel who are aware of the

hazards involved (for example, fire and electrical shock). Where maintenance can be performed without
power applied, the power should be removed.

Introduction

Before attempting to troubleshoot this instrument, ensure that the fault is with the instrument itself and not with an
associated circuit. The performance test enables this to be determined without having to remove the covers from the supply.

The most important aspect of troubleshooting is the formulation of a logical approach to locating the source of trouble. A
good understanding of the principles of operation is particularly helpful, and it is recommended that Chapter 4 of this
manual be reviewed before attempting to troubleshoot the unit. Often the user will then be able to isolate a problem simply
by using the operating controls and indicators. Once the principles of operation are understood, refer to the following
paragraphs.

Table 2-1 lists the test equipment for troubleshooting. Chapter 6 contains schematic diagrams and information concerning
the voltage levels and waveforms at many of the important test points. Most of the test points used for troubleshooting the
supply are located on the control board test "fingers", which are accessible close to the top of the board. See Table 3-1.

3

If a component is found to be defective, replace it and re-conduct the performance test. When a component is replaced,
refer to Calibration Procedure (Chapter 2). It may be necessary to perform one or more of the adjustment procedures after a
component is replaced.

Initial Troubleshooting Procedures

If a problem occurs, follow the steps below in sequence:

a. Check that input power is available, and check the power cord and rear-panel circuit breaker.
b. Check that the settings of mode switch A2S1 are correct for the desired mode of operation. (See Operating Manual).
c. Check that all connections to the power supply are secure and that circuits between the supply and external devices are

not interrupted.

d. If the power supply fails turn-on self-test or gives any other indication of malfunction, remove the unit from the

operating system before proceeding with further testing.

Some circuits on the power mesh are connected directly to the ac power line. Exercise extreme caution

when working on energized circuits. Energize the supply through an isolation transformer to avoid

shorting ac energized circuits through the test instrument's input leads. The isolation transformer must
have a power rating of at least 1KVA. During work on energized circuits, the safest practice is to
disconnect power, make or change the test connections, and then re-apply power.

Make certain that the supply's ground terminal (┴) is securely connected to an earth ground before applying
power. Failure to do so will cause a potential shock hazard that could result in personal injury.

23

Table 3-1. Control Board Test Connector, A2J7

PIN NO. SIGNAL NAME Vdc WAVEFORM/CONDITIONS SOURCE

Digital-Circuits Bias & Reference Voltages

1 +5V 5.0 A2Q3 (emitter)
22 + 20V(5V UNREG) 20.0 with 120Hz & 45KHz ripple A1CR6, A1CR7
14 2.5V ref 2.50 A2U9 (OUT)
6 0.5V ref 0.50 A2R79,A2R80

Analog-Circuits Bias Voltages

2 + 15V 15.0 A2U12 (OUT)
21 - 15V -15.0 A2U4 (OUT )

Status Signals

17

16

13

11

12

Control Signals

CV

CC

OV

DROPOUT

OT

25 PWM OFF <0.5
26 PWM ON <1.0

TTL Lo if in CV operation A2Q6C-7 (collector)

TTL Lo if in CC operation A2Q6F-14 (collector)

TTL Hi if not OVP shutdown A2U11D-11

TTL Hi if ac mains okay A2U17D-11

TTL Hi if not overtemp shutdown A2U11B-6

1.7

µs TTL pulses, 20KHz

1.7

µs TTL pulses, 20KHz

U1A-5

U2B-6
18 Ip MONITOR <0.5 1V pk, ½ sawtooth, 20KHz A2CR26 (cathode)
8

15

INHIBIT

DOWN PROGRAM

TTL hi if not remotely inhibited A2R185C, U19A-2

1.2-3.0 A2CR21, A2CR27

7 OVP PROGRAM 1/10 OVP (6023A) e.g.: 2Vdc if OVP set to 20 A3R6 (wiper)

1/30 OVP (6028A)

5

19

Commons & Current-Monitor

CLR OV

2 PCLR

4 L COMMON 0.0 common return for all bias

+5V inverted OV reset line A7U29-5

+5V if +5V bias OK A2Q60-9

A2C20 (-), A2R50,

voltages, and status and control

A2U6-4

signals

9 M COMMON 0.0 common return for 2.5V ref.

A2R83, A21-20

and 0.5V ref.

10 I-TEST

≈0.005 ( Iout)

inboard-side monitoring res. A1R3,A1T2

3 NOT USED

24

Electrostatic Protection

The following caution outlines important precautions which should be observed when working with static sensitive
components in the power supply.

This instrument uses components which can be damaged by static charge. Most semiconductors can
suffer serious performance degradation as a result of static charges, even though complete failure may
not occur. The following precautions should be observed when handling static-sensitive devices.

a. Always turn power off before removing or installing printed-circuit boards.
b.

Always stored or transport static-sensitive devices (all semiconductors and thin-film devices) in conductive material.

Attach warning labels to the container or bag enclosing the device.

c.

Handle static-sensitive devices only at static-free work stations. These work stations should include special conductive

work surfaces (such as Agilent Part No. 9300-0797) grounded through a one-megohm resistor. Note that metal table
tops and highly conductive carbon-impregnated plastic surfaces are too conductive; they can act as large capacitors and
shunt charges too quickly. The work surfaces should have distributed resistance of between 10

d.

Ground all conductive equipment or devices that may come in contact with static-sensitive devices or subassemblies

containing same.

e.

Where direct grounding of objects in the work area is impractical, a static neutralizer should be used (ionized air

blower directed at work). Note that this method is considerably less effective than direct grounding and provides less
protection for static-sensitive devices.

f.

While working with equipment on which no point exceeds 500 volts, use a conductive wrist strap in contact with skin.

The wrist strap should be connected to ground through a one-megohm resistor. A wrist strap with insulated cord and
built-in resistor is recommended, such as 3M Co. No. 1066 (Agilent Part No. 9300-0969 (small) and 9300-0970
[large]).

6

and 10l2 Ω per square.

Do not wear a conductive wrist strap when working with potentials in excess of 500 volts; the one-megohm
resistor will provide insufficient current limiting for personal safety.

g. All grounding (device being repaired, test equipment, soldering iron, work surface, wrist strap, etc.) should be done to

the same point.

h.

Do not wear nylon clothing. Keep clothing of any kind from coming within 12 inches of static-sensitive devices.

i.

Low-impedance test equipment (signal generators, logic pulsers, etc.) should be connected to static-sensitive inputs

only while the components are powered.

j.

Use a mildly activated rosin core solder (such as Alpha Metal Reliacor No. 1, Agilent Part No. 8090-0098) for repair.

The flux residue of this type of solder can be left on the printed circuit board. Generally, it is safer not to clean the
printed-circuit board after repair. Do not use Freon or other types of spray cleaners. If necessary, the printed-circuit
board can be brushed using a natural-bristle brush only. Do not use nylon-bristle or other synthetic-bristle brushes. Do
not use high-velocity air blowers (unless ionized).

k.

Keep the work area free of non-conductive objects such as Styrofoam-type cups, polystyrene foam, polyethylene bags,

and plastic wrappers. Non-conductive devices that are necessary in the area can be kept from building up a static
charge by spraying them with an anti-static chemical (Agilent Part No. 8500-3397).

l.

Do not allow long hair to come in contact with static-sensitive assemblies.

m.

Do not exceed the maximum rated voltages specified for the device.

Repair and Replacement

Repair and replacement of most components in the power supply require only standard techniques that should be apparent
to the technician. The following paragraphs provide instructions for removing certain assemblies and components for which
the procedure may not be obvious upon inspection.

25

To avoid the possibility of personal injury, remove the power supply from operation before opening the
cabinet. Turn off ac power and disconnect the line cord, load, and remote sense leads before attempting
any repair or replacement.

When replacing any heatsink-mounted components except thermostat, smear a thin coating of heatsink
compound between the component and heatsink. If a mica insulator is used, smear a thin coating of
heatsink compound on both sides of the mica insulator.

Do not use any heatsink compound containing silicone, which can migrate and foul electrical contacts
elsewhere in the system. An organic zinc oxide cream, such as American Oil and Supply Company
Heatsink Compound #100, is recommended.

Most of thc attaching hardware in this unit is metric. The only non-metric (sometimes called English or
inch) fittings are listed below. Be careful when both types of screws are removed not to get them
mixed up.

a. Lock-link/shelf-mounting blocks (4 on rear panel, one at each corner).
b.

Rear-panel fuse holder.

c.

Rear-panel ground binding post.

d.

Strap-handle screws (2).

e.

Screws that secure side chassis to front-frame casting (8, 4 on each side).

f.

Screws that secure front-panel to front-frame casting (4, 2 on top and 2 on bottom).

Top Outside Cover Removal. Remove three screws, the rear handle screw (Phillips, 10x32) and two top-rear corner

screws (Pozidriv, M4x.7) using a Size 1, Pozidriv screwdriver. A Phillips head screwdriver does not fully seat into
Pozidriv screws and risks stripping the heads. Do not remove the front handle screw, as the retaining nut will fall into the
unit. Remove the top cover by sliding it to the rear and lifting at the front.

Bottom Cover Removal. Remove only for repair of main board. Remove two bottom-rear corner screws. (Pozidriv,

M4x.7) and remove the bottom cover by sliding it to the rear. You do not need to remove the unit's feet.

Inside Top Cover Removal. The unit includes an inside cover which secures the vertical board assemblies. Remove the

inside cover for repair but not for calibration. Remove the six mounting screws (Pozidriv, M4x.7) – three on each side and
five board fastening screws (Pozidriv, M4x.7) all on top. Remove the inside cover by lifting at the front edge.

When installing the inside cover, insert it first at the right side. While holding it tilted up at the left, reach through the
cutouts in the cover and fit the top tabs of the A2 control board into the mating slots in the cover. With the top cover in
place reach through the cutout above the A4 power mesh board, align the board-fastening screw holes, and replace the rear­most screw to secure the A4 board. Press the inside cover down firmly while tightening screws that secure cover to chassis.
Complete the installation by replacing the remaining ten screws. Be careful when replacing printed-circuit assemblies and
covers not to bend any boards or components.

A2 Control Board Removal

After removing the inside cover, remove the A2 board by lifting first at the front edge and than pulling it up and out of the
unit. Two connectors hold the A2 board at its bottom edge.

When installing the A2 board, insert it first at the rear of the unit. While holding it tilted up at the front, fit the A2TB1
terminal strip into the mating cutout in the rear panel. Then lower the A2 board's bottom connectors into the mating
connectors on the main board. Press the A2 board into the connectors.

26

A4 Power Mesh Board Removal

After removing the inside cover, remove the A4 power mesh board by lifting, using the large aluminum heatsink as a
handle. Two connectors hold the A4 board at its bottom edge.
When installing the A4 power mesh board, lower it vertically into its connectors and press in place.

A3 Front-Panel Board Removal

Remove the A3 front-panel board by first removing the entire front-panel assembly. You do not need to remove the top
cover. Follow this procedure:

a.

Remove the top plastic insert by prying up with a flat-blade screwdriver, and remove the front feet by lifting the tabs

and sliding toward the front of the unit.

b.

Remove the four front-panel assembly mounting screws (Phillips 8-32) on the top and bottom at the corners using a

Pozidriv or Phillips head screwdriver (Phillips head screwdriver may be used only with these four screws).

c.

Gently pull the front-panel assembly away from the unit as far as permitted by the connecting cables.

d.

Remove the ground-wire screw (Pozidriv, M4x.7) holding the green-yellow ground wire.

e.

Note the locations of the four power-wire connections to the power switch and then unplug the quick-connect plugs.

f.

Unplug the W3 3-wire cable from connector A1J3 on the A1 main board.

g.

Remove the A3 board from the front-panel assembly by removing the five mounting screws (Pozidriv, M4x.7)

Install the A3 Board by reversing the steps above. The power wires are correctly connected to the power switch wires if
they do not cross each other.

A1 Main Board Removal

Removing the A1 main board requires removing the rear panel, all boards except the A3 front-panel board, and 17 A1
board mounting screws. Component-access cutouts in the bottom inside cover allow unsoldering most A1-board
components for repair without removing the A1 board.

To remove the A1 board, proceed as follows:

a.

Remove the A2 and A4 boards according to the above instructions.

b.

Detach the rear panel by removing the four mounting screws (Pozidriv, M4x.7) two on each side. Gently pull the rear

panel away from the unit as far as permitted by the four wires connected to the A1 board.

c.

Unplug the W1 ribbon cable from connector A1J1.

d.

Remove the A1 board by removing the 17 mounting screws (Pozdriv, M4x.7).

e.

Note locations and the unplug the two ac power wires and the two fan wires to the A1 board.

Overall Troubleshooting Procedure

Perform the troubleshooting and repair procedures which follow only if you are trained in equipment

service and are aware of the danger from fire and electrical-shock hazards. Some of the procedures include
removing the unit's protective covers which may expose you to potentially lethal electrical shock.
Whenever possible, make test connections and perform service with the power removed.

After performing the Initial Troubleshooting Procedures, focus on developing a logical approach to locating the source of
the trouble. The underlying strategy for the troubleshooting procedures here is to guide you to the faulty circuit nodes
which have improper signals or voltages. It relies on you to identify the particular functional circuit to troubleshoot from
symptom tables and by understanding how the unit works. It then relies on you to discover the defective component or
components which cause the faulty circuit nodes. So, read the BLOCK DIAGRAM overview in Chapter 4 and read the
functional circuit descriptions for the circuits that you suspect may be defective. Then return to this section for help finding
the faulty circuit nodes.

27

Table 3-1 gives the signals for each of the test points on the control board test connector. This connector is provided in
service kit P/N 06033-60005. The measurements given here include bias and reference voltages as well as power supply
status signals and waveform information.

Table 3-2 provides troubleshooting information based on the status of the PWM-ON and PWM-OFF signals which drive
the PFETs. This table is used for no-output failures.

Tables 3-3 and 3-4 give measurements for the test points on the A3 front-panel board and possible failure symptoms
respectively.

Table 3-5 describes possible symptoms for overall performance failures of the power supply. It is necessary to have a
properly working front-panel before using this table.

Chapter 6 contains schematic diagrams and voltage levels, and component location diagrams to help you locate components
and test points.

Make most voltage measurements (except DC-to-DC Converter and ac mains-connected circuits) referenced to the unit's
output common which is accessible at rear-panel terminal VM. All voltages are

± 5% unless a range is given.

Using the Tables

Typically there will be two types of power supply failures; no-output and performance failures.

1.

No-OUTPUT FAILURE: Start with the TROUBLESHOOTING NO-OUTPUT FAILURES section which references

Tables 3-1 and 3-3.

2.

PERFORMANCE FAILURE: If the power supply produces an output but does not perform to specifications, begin by

verifying the measurements at the A2J7 test connector using Table 3-1. Next, verify the front-panel by doing the
procedure outlined in the FRONT-PANEL TROUBLESHOOTING section. After the front-panel has been verified
consult Table 3-5 for the performance failure symptom which seems closest to the one observed and proceed to the
functional circuit given for that failure.

The circuits referenced in Tables 3-2 and 3-5 are derived from functional blocks of circuits in the power supply. These
blocks are given in the Power Supply Blocks section starting on page 35. Troubleshooting information for each block will
include a brief description of the circuit involved. The columns provided in each block are as follows:

NODE: This column lists the nodes where the measurements should be taken. In some cases this will be

stated as NODE ( + ) and NODE (- ) where the first is the test node and the second is the
reference.

SETUP: If a certain setup is required for the measurement, it will be given in this column.

MEASUREMENT: This column indicates what the expected measurement is for the given node.

SOURCE: If applicable, the components which generate the signal will be provided in this column .

Some blocks will have Input and Output sections. The input section will have a source column to indicate which
components generated the measured signal. The output section will list all the important output signals from that block.
However, because the outputs of one block are the inputs to another, the schematic should be consulted if an output
measurement is incorrect. This will indicate the next circuit block to be trouble shot.

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Main Troubleshooting Setup

Figure 3-1 shows the troubleshooting setup for troubleshooting all of the unit except the front-panel and initial no output
failures (See page 31). The external power supply provides the unit's internal bus voltage. The ac mains cord connects to
the unit's A1T3 bias transformer via an isolation transformer, thereby energizing the bias supplies, but it does not connect to
the input rectifier and filter because that would create the bus voltage. With the external supply the unit operates as a
dc-to-dc converter. The supply biases the A4Q3 and A4Q4 PFETs with a low voltage rather than the 320Vdc bus voltage.
This protects the PFETs from failure from excess power dissipation if the power-limit comparator or the off-pulse circuitry
are defective. It also reduces the possibility of electrical shock to the troubleshooter.

Figure 3-1. Main Troubleshooting Setup

The troubleshooting setup of Figure 3-1 connects high ac mains voltage to the A1F2 fuse, the A1S2 Mains-

Voltage Select Switch, the fan and printed-circuit traces at the left edge of the A1 main board. Be
extremely careful when working on the unit with the protective inside cover removed to avoid touching the
ac mains voltage.

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As a convenience in implementing the troubleshooting setup, prepare cord sets as shown in Figure 3-2. This facilitates
connecting the unit's input power receptacle to the external supply and connecting the bias transformer to the ac mains.

Figure 3-2. Modified Mains Cord Set For Troubleshooting

With the mains cord unplugged proceed as follows:

a.

Remove the top cover and the inside cover as described on page 26. Set switch S4 (front-left corner of the A1 main

board) in TEST position.

If switch is not in the TEST position and remains in the NORM position, completion of step e below will

allow the unit to develop its 320Vdc bus voltage across PFETs A3Q3 and A3Q4 and will connect the ac

mains voltage to the output of the external power supply. This will probably damage the external supply

and is a shock hazard to you.

b. Install control board test connector onto the A2J3 card edge fingers.
c.

Connect a 50Ω, 10W, load resistor to the unit's output terminals.

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