Crown MA-5002-VZ Service manual

Macro-Tech®

POWER AMPLIFIER

SERVICE MANUAL

Models:

MA-5002VZ

and

SmartAmp

ODEP®

®

and

VZ

™
®

are

are

Some models may be exported under the name

© 2000 by Crown International, Inc., P.O. Box 1000, Elkhart, Indiana 46515-1000 U.S.A.
Telephone: [phone]. Trademark Notice:
trademarks and
registered trademarks of Crown International, Inc. Other trademarks are the property of their
respective owners.

Amcron®, Crown®, IOC®, IQ System®, Macro-Tech

Grounded Bridge™, PIP2™

Amcron

,®

130446-1

02-00

Rev. A

MA-5002VZ Service Manual

The information furnished in this manual does not include all of the details of design, production, or variations
of the equipment. Nor does it cover every possible situation which may arise during installation, operation or
maintenance. If you need special assistance beyond the scope of this manual, please contact the Crown
Technical Support Group.

Mail:

P.O. Box 1000 Elkhart IN 46515-1000

Shipping:

Plant 2 SW 1718 W. Mishawaka Road Elkhart IN 46517

Phone:

[phone] / [phone]

FAX:

[phone]

130446-1 Rev. A

CAUTION

TO PREVENT ELECTRIC SHOCK DO

NOT REMOVE TOP OR BOTTOM
COVERS. NO USER SERVICEABLE
PARTS INSIDE. REFER SERVICING

TO QUALIFIED SERVICE

PERSONNEL. DISCONNECT

POWER CORD BEFORE REMOVING

REAR INPUT MODULE TO ACCESS

GAIN SWITCH.

WARNING

AVIS

À PRÉVENIR LE CHOC

ÉLECTRIQUE N’ENLEVEZ

PAS LES COUVERTURES.

RIEN DES PARTIES

UTILES À L’INTÉRIEUR.

DÉBRANCHER LA BORNE

AVANT D’OUVRIR LA

MODULE EN ARRIÈRE.

TO REDUCE THE RISK OF ELECTRIC

SHOCK, DO NOT EXPOSE THIS

EQUIPMENT TO RAIN OR MOISTURE!

The lightning bolt
triangle is used to
alert the user to the
risk of electric shock.

II

The exclamation point
triangle is used to alert the
user to important operating
or maintenance instructions.

©2000 Crown International, Inc.

130446-1 Rev. A

MA-5002VZ Service Manual

Revision History

Revision Number

Rev. A

Date

02-2000 Initial Printing

Comments

©2000 Crown International, Inc.

III

MA-5002VZ Service Manual

130446-1 Rev. A

This page intentionally left blank

IV

©2000 Crown International, Inc.

130446-1 Rev. A

1 Introduction ............................................................................ 1-1

2 Specifications ......................................................................... 2-1

3 Voltage Conversion................................................................ 3-1

4 Circuit Theory ........................................................................ 4-1

MA-5002VZ Service Manual

Table of Contents

1.1 Introduction ................................................................................1-1

1.2 The MA “02” Series Amplifiers ...................................................1-1

1.3 Scope.........................................................................................1-1

1.4 Warranty.....................................................................................1-1

4.1 Overview .................................................................................... 4-1

4.2 Grounded Bridge Theory ...........................................................4-1

4.2.1 Grounded Bridge Operation ............................................. 4-2

4.2.2 Output Stage Circuitry.......................................................4-3

4.3 VZ Power Supply........................................................................4-4

4.3.1 VZ Supply Operation......................................................... 4-4

4.3.2 VZ Supply Circuitry ...........................................................4-5

4.4 ODEP Theory .............................................................................4-6

4.4.1 ODEP Operation................................................................4-6

4.4.2 ODEP Circuitry .................................................................. 4-7

4.5 Front End Theory........................................................................4-8

4.5.1 Balanced Gain Stage ........................................................ 4-8

4.5.2 Variable Gain Stage ..........................................................4-8

4.5.3 Error Amp .......................................................................... 4-8

4.5.4 Compessor........................................................................ 4-9

4.5.5 Loudspeaker Offset Integration ........................................4-9

4.5.6 Voltage Translator and LVA Stages ..................................4-9

4.5.7 Inverting Stages ................................................................4-9

4.6 Protection Systems ....................................................................4-9

4.6.1 Soft Start............................................................................ 4-9

4.6.2 Over-voltage....................................................................4-11

4.6.3 DC/LF .............................................................................. 4-11

4.6.4 Commom Mode Output Current......................................4-12

4.6.5 Output Thermal ...............................................................4-12

4.6.6 Transformer Thermal ....................................................... 4-12

4.6.7 FET Thermal ....................................................................4-12

4.6.8 Power Loss...................................................................... 4-13

4.6.9 Fan Control...................................................................... 4-13

4.7 Display ..................................................................................... 4-13

4.8 Mono Modes ............................................................................4-13

4.8.1 Bridge Mono....................................................................4-13

4.8.2 Parallel Mono...................................................................4-14

©2000 Crown International, Inc.

V

MA-5002VZ Service Manual

5 Maintenance........................................................................... 5-1

5.1 Cautions and Warnings..............................................................5-1

5.2 General Information ...................................................................5-1

5.3 Troubleshooting ........................................................................ 5-1

5.3.1 Pre-AC-Checks ................................................................5-1

5.3.2 LED Checks .....................................................................5-2

5.4 Test Procedures.........................................................................5-4

5.4.1 Standard Initial Conditions ................................................ 5-4

5.4.2 Equipment Required .........................................................5-4

6 Parts ....................................................................................... 6-1

6.1 General Information ..................................................................6-1

6.2 Ordering and Receiving Parts ..................................................6-1

6.2.1 Terms ..................................................................................... 6-1

6.2.2 Shipment ................................................................................6-1

130446-1 Rev. A

Table of Contents

7 Exploded View Parts ............................................................ 7 -1

8 Module and Schematic Information.................................... 8 -1

9 Module Parts.......................................................................... 9-1

10 Schematics ........................................................................ 10-1

VI

©2000 Crown International, Inc.

130446-1 Rev. A

1 Introduction

1.1 Introduction

This manual contains complete service information on
the
to be used in conjunction with the Reference Manual;
however, some important information is duplicated in
this Service Manual in case the Reference Manual is
not readily available.

NOTE: THE INFORMATION IN THIS MANUAL IS
INTENDED FOR USE BY AN EXPERIENCED TECH­NICIAN ONLY!

1.2 The MA “02” Series Amplifiers

The
fiers designed for pro sound reinforcement. Macro­T ech amplifiers ar e designed to provide enormous lev­els of pure, undistorted power in a rugged low-profile
package, utilizing Crown's patented

Bridge

patented
amplifier working under extreme conditions that would
shut down a lesser amplifier . Crown's new Macro-Tech
“02” series amplifiers feature Crown's enhanced

PIP2™

system. The PIP2 expansion system makes it easy to
tailor the amplifier to a specific application. Providing
high power amplification from 20 Hz to 20 kHz with
minimum distortion, Macro-T ech series amplifiers fea­ture balanced inputs with bridged and parallel mono-

®

Crown

MA-5002VZ power amplifier . It is designed

Macro-Tech

®

series is a complete family of ampli-

Grounded

™ output topology. They also employ Crown's

(Programmable Input Processor) expansion

ODEP

®

protection circuitry, which keeps the

MA-5002VZ Service Manual

phonic capability . The MA-5002VZ includes additional
features not found on other Macro-Tech series models
including switchable compression, switchable loud­speaker offset integration (LOI), and I
cation.

LOAD/ILIMIT indi-

1.3 Scope

This Service Manual in intended to apply to all ver­sions of the MA-5002VZ amplifier. The Parts Listings
include parts specific for the US version and the Euro­pean version (E13). For parts specific only to other
versions contact the Crown Technical Support Group
for help in finding part numbers.

1.4 Warranty

Each Reference Manual contains basic policies as re­lated to the customer. In addition, it should be stated
that this service documentation is meant to be used
only by properly trained personnel. Because most
Crown products carry a 3-Year Full Warranty (includ­ing round trip shipping within the United States), all
warranty service should be referred to the Crown Fac­tory or Authorized Warranty Service Center. See the
applicable Reference Manual for warranty details. To
find the location of the nearest Authorized Warranty
Service Center or to obtain instructions for receiving
Crown Factory Service, please contact the Crown T ech­nical Support Group (within North America), or your
Crown/Amcron Importer (outside North America). If you
are an Authorized W arranty Service Center and have
questions regarding the warranty of a product, please
contact the Field Service Manager or the Technical
Support Group.

©2000 Crown International, Inc.

Crown Customer Service

Technical Support Group

Factory Service

Parts Department

Mailing Address:

1718 W. Mishawaka Rd., Elkhart IN 46517

P.O. Box 1000, Elkhart IN 46515

Shipping Address:

Phone: [phone]

Toll Free: [phone]

Fax: [phone]

http://www.crownaudio.com

Plant 2 S. W.

Introduction 1-1

MA-5002VZ Service Manual

130446-1 Rev. A

1-2 Introduction

Figure 1.1 MA-5002VZ Front and Rear Views

©2000 Crown International, Inc.

130446-1 Rev. A

2 Specifications

Specifications

The following applies to 120-VAC, 60-Hz units in Stereo mode with 8-ohm loads and an
input sensitivity of 26-dB gain unless otherwise specified. Specifications for units
supplied outside the U.S.A. may vary slightly at different AC voltages and frequencies.

Power

Output Power

20 Hz– 20 kHz

*

**

1 kHz

MA-5002VZ

2-ohm Dual (per ch.)

4-ohm Dual (per ch.)
8-ohm Dual (per ch.)
4-ohm Bridge-Mono
8-ohm Bridge-Mono

*1 kHz Power: refers to maximum average power in watts
at 1 kHz with 0.1% THD.

**20 Hz– 20 kHz Power: refers to maximum average power
in watts from 20 Hz to 20 kHz with 0.1% THD.

Power

2,500W
2,000W

1,300W
5,000W
4,000W

Load Impedance: Safe with all types of loads. Rated for 2 to 8

ohms in Stereo, 4 to 16 ohms in Bridge-Mono and 1 to 4 ohms in
Parallel-Mono mode.

Voltage Gain to 1-kHz, 8-ohm rated output:

132:1 ±12% or 42 dB ±1 dB gain at 0.775 volt sensitivity;
71:1 ±12% or 37 dB ±1 dB gain at 1.4-volt sensitivity;
20:1 ±3% or 26 dB ±0.25 dB gain at the maximum level setting.
Required AC Mains: 50 or 60 Hz; 100-, 120-, 200-, 208-, 230-,
240- VAC (±10%).

AC Line Current,

Current, voltage and frequency requirements are provided on the
unit’s back panel.

At Idle: All units draw 90 watts or less.
AC Line Connector: 10 AWG cordset with NEMA TT30P plug is

provided on 120-VAC, 60-Hz North American units.

Performance

Frequency Response: ±0.1 dB from 20 Hz to 20 kHz at 1 watt (see

Figure 2.3).
Phase Response: ±10 degrees from 10 Hz to 20 kHz at 1 watt (see

Figure 2.2).

Signal-to-Noise Ratio,A-weighted:

Better than 105 dB below rated 1-kHz power.
Total Harmonic Distortion (THD): 1-kHz rated power, 0.05% or

less true THD.
Intermodulation Distortion (IMD): (60 Hz and 7 kHz at 4:1) Less

than 0.05% from rated power to 35 dB below rated power at 8
ohms.

Damping Factor: Greater than 1,000 from 10 Hz to 400 Hz (see
Figure 2.4).

Controlled Slew Rate: (Slew rates are limited to useful levels for
ultrasonic/RF protection.) Greater than 30 volts per microsecond.

Power

2,155W
1,775W

1,090W

3,670W

MA-5002VZ Service Manual

Controls

Compressor: A three-position back-panel switch is used to control

each channel’s input compressor. The “fast” setting provides an
attack time of 4 milliseconds and a release time of 300 millisec­onds; the “slow” setting provides an attack time of 12 milliseconds
and a release time of 600 milliseconds; the “off” setting defeats
output-driven compression.

Enable: A front-panel push button used to turn the amplifier on and
off.

Input Ground Lift: A two-position back-panel switch located on the
PIP2-FXQ used to isolate the input audio signal grounds from the
AC (chassis) ground.

Level: A front-panel rotary potentiometer for each channel with 31
detents used to control the output level.

Loudspeaker Offset Integration: A two-position back-panel switch
for each channel used to turn the loudspeaker protection circuitry
on and off. The circuitry protects against DC, off-center woofer
cone movement, and unwanted subsonic and ultrasonic frequen­cies.

Sensitivity: A three-position back-panel switch for each channel
used to select input sensitivity: 0.775 volts or 1.4 volts for
standard 1-kHz power, or a 26 dB voltage gain.

Stereo/Mono: A three-position back-panel switch used to select
Stereo, Bridge-Mono or Parallel-Mono mode.

VZ Mode: A four-position switch for each channel inside the front­panel used to control the switching mode of the VZ power supplies.

Indicators

Enable: An amber front-panel LED that shows the on/off status of

the low-voltage power supply.
Signal/IOC: A green front-panel LED for each channel that flashes

to show amplifier output. If a channel’s output waveform differs
from its input by 0.05% or more, the indicator flashes brightly to
show distortion.

ODEP: An amber front-panel LED for each channel that shows
thermal-dynamic energy reserve. Normally, each ODEP indicator is
lit to show available reserve energy. In the rare event that a channel
has no reserve, its indicator will dim in proportion to ODEP
limiting.

ILoad/ILimit: A two-color (green/red) LED for each channel that
shows load current and limit current. They glow green to indicate
load current flowing out the amplifier, and they turn red when
maximum current is being delivered to the load.

Input/Output

Input Connectors: Balanced three-pin XLR and balanced ¼-inch

(6.35-mm) TRS connectors are provided on the factory-installed
PIP2-FXQ module.

Input Impedance: Greater than 10 ohms, balanced. Greater than 5
ohms, unbalanced.

Input Sensitivity: Settings include 0.775 volts or 1.4 volts for
standard 1 kHz power, or a 26-dB voltage gain.

Output Connectors: A multifunction, high-current output block is
provided. Crown output blocks include three pairs of connectors
for each channel (a total of 12 connectors). This allows multiple
loudspeakers to be easily connected to each channel. High current
screw terminals and banana jacks are provided which accept spade
lugs, banana plugs or bare wire.

Output Impedance: Less than 10 milliohms in series with less than

2.5 microhenries(see Figure 2.5).

©2000 Crown International, Inc.

Specifications 2-1

MA-5002VZ Service Manual

130446-1 Rev. A

DC Output Offset: ±10 millivolts.

Output Signal

Stereo: Unbalanced, two-channel.
Bridge-Mono: Balanced, single-channel. Channel 1 controls are

active; Channel 2 controls are removed from operation.
Parallel-Mono: Unbalanced, single-channel. Channel 1 controls are

active; Channel 2 controls are by passed.

Protection

Macro-Tech amplifiers ar e protected against shorted, open or
mismatched loads; overloaded power supplies; excessive
temperature; chain destruction phenomena; input overload
damage; and high-frequency blowups.They also protect loud­speakers from input/output DC and turn-on/turn-off transients.

If unreasonable operating conditions occur, the patented ODEP
circuitry will proportionally limit the drive level to protect the
output transistor stages, particularly in the case of elevated
temperature. Transformer overheating will result in a temporar y
shutdown of the affected channel; when it has cooled to a safe
temperature, the transformer will automatically reset itself.
Controlled slew rate voltage amplifiers protect against RF burnouts.

And input overload protection is provided by the input compres­sors and current-limiting resistance at the input.

Tu rn On: The four second turn-on delay prevents dangerous turn­on transients. It also has “soft start” to avoid tripping the AC circuit
breaker by gradually bringing the supplies up to full voltage.

Accessories: Crown PIP and PIP2 modules including IQ-PIP

modules.

Construction

Steel chassis with durable black finish, aluminum front panel with
Lexan overlay, and specially designed flow-through ventilation from
front to back panels.

Cooling: Internal heat sinks with on-demand, proportional forced­air cooling controlled by ODEP. Includes custom heat diffusers and
patented circuitry to promote uniform dissipation.

Dimensions: 19-inch (48.3-cm) standard rack mount width (EIA
RS-310-B), 5.2-inch (13.3-cm) height, 15.875-inch (40.3-cm)
depth behind mounting surface, and 2.875 inches (7.3 cm) in front
of mounting surface (see Figure 2.1). Allow 3 inches (7.6 cm)
behind the back panel for adequate air flow.

Approximate Weight: 77 pounds, 9 ounces (35.2 kg) net; 88
pounds, 10 ounces (40.2 kg) shipping weight.

Figure 2.1 Dimensions

+45˚

0˚

–45˚

®

100 1 K 10 K 20 K

TEF

FREQUENCY (Hz)

Figure 2.2 Typical Phase Response

2-2 Specifications

©2000 Crown International, Inc.

130446-1 Rev. A

MA-5002VZ Service Manual

Figure 2.3 Typical Frequency Response

Figure 2.4 Typical Damping Factor

Figure 2.5 Typical Output Impedance

©2000 Crown International, Inc.

Specifications 2-3

MA-5002VZ Service Manual

130446-1 Rev. A

This page intentionally left blank

2-4 Specifications

©2000 Crown International, Inc.

130446-1 Rev. A

3 Voltage Conversion

The MA-5002VZ power amplifier may easily be con­verted to a variety of AC mains voltages and may oper­ate at 50 or 60 Hz. Complete directions to accomplish
line voltage and/or frequency changes are found on a
label under the top cover of the unit. For convenience
this information is duplicated here and on the following
page.

Control Board Wiring for Different AC Voltages

NO.**

100 V

P712
P711

P724B

BLU*

P707

BLK/GRN

P704

--NONE--

P705

--NONE--

P710

WHT/GRN

P709

WHT/RED

P708

WHT/YEL

P703

BLK/YEL

P701
P700
P702

GRN/YEL

P713

BLK/YEL

P714

WHT/YEL

P722

BRN*

P749

WHT/RED

P750

WHT/GRN

P718

--NONE--

P716

--NONE--

P721

BLK/GRN

P719
P715

P724A

BLU*

P736

GRN/YEL

P735
P734
P742

BLK/YEL

P737

WHT/YEL

P744

WHT/RED

P743

WHT/GRN

P738

--NONE--

P739

--NONE--

P745

BLK/GRN

P724C

BLU*

P741
P740

P729***
P730***

Figure 3.1 Voltage/Frequency Conversion Chart

120 V 200 V 208 V 230 V 240 V

BLK

BLK

WHT

GRY
GRY

BLK

WHT

GRY
GRY

WHT

BLK

120 V Position 240 V Position

BLK

WHT

BLU*

BLK/YEL

--NONE--

--NONE-­WHT/YEL
WHT/RED

WHT/GRN

BLK/GRN

GRY

GRY
GRN/YEL
BLK/GRN

WHT/GRN

BRN*

WHT/RED

WHT/YEL

--NONE--

--NONE--

BLK/YEL

BLK

WHT

BLU*

GRN/YEL

GRY

GRY
BLK/GRN

WHT/GRN
WHT/RED

WHT/YEL

--NONE--

--NONE--

BLK/YEL

BLU*

WHT

BLK

BLK

--NONE-­ BLU*

BLK/GRN

BLK/YEL

WHT
WHT/RED
WHT/GRN
WHT/YEL

--NONE-­GRY
GRY

GRN/YEL

--NONE--

WHT/YEL

BRN*
WHT/GRN
WHT/RED

WHT

BLK/YEL

BLK/GRN

BLK

--NONE-­ BLU*

GRN/YEL

GRY
GRY

--NONE--

WHT/YEL
WHT/GRN
WHT/RED

WHT

BLK/YEL

BLK/GRN

BLU*

--NONE--

BLK

--NONE-­ BLU*

BLK/GRN

BLK/YEL

WHT

WHT/YEL

WHT/GRN

WHT/RED

--NONE--

GRY
GRY

GRN/YEL

--NONE--

WHT/RED

BRN*

WHT/GRN

WHT/RED

WHT

BLK/YEL

BLK/GRN

BLK

--NONE-­ BLU*

GRN/YEL

GRY
GRY

--NONE--

WHT/RED

WHT/GRN

WHT/YEL

WHT

BLK/YEL

BLK/GRN

BLU*

--NONE--

BLK

BLK

--NONE-­ BLU*

BLK/YEL

WHT

BLK/GRN
WHT/YEL
WHT/GRN
WHT/RED

--NONE-­GRY
GRY

GRN/YEL

--NONE--

WHT/RED

BRN*
WHT/GRN
WHT/YEL

BLK/GRN

WHT

BLK/YEL

BLK

--NONE-­ BLU*

GRN/YEL

GRY
GRY

--NONE--

WHT/RED
WHT/GRN
WHT/YEL

BLK/GRN

WHT

BLK/YEL

BLU*

--NONE--

BLK

BLK

--NONE-­ BLU*

BLK/YEL

WHT
BLK/GRN
WHT/YEL
WHT/RED
WHT/GRN

--NONE-­GRY
GRY

GRN/YEL

--NONE--

WHT/GRN

BRN*
WHT/RED
WHT/YEL
BLK/GRN

WHT

BLK/YEL

BLK

--NONE-­ BLU*

GRN/YEL

GRY
GRY

--NONE--

WHT/GRN
WHT/RED
WHT/YEL
BLK/GRN

WHT

BLK/YEL

BLU*

--NONE--

BLK

MA-5002VZ Service Manual

INSTRUCTIONS

CAUTION: Because there is a risk of

electric shock, only a qualified technician

should change the line voltage configuration.

1. Turn the amplifier off and disconnect it from the AC
power source. (The enable switch alone does not re­move lethal voltage from the line cord.) W ait at least 10
seconds before proceeding.

2. Drain any remaining energy from the power supplies
by shorting them as follows: Touch a 100 ohm, 10 watt
resistor across terminals A1 and A2 and across B1 and
B2 as shown in the illustration. The resistor should be
held across the terminals for 10 seconds. Be careful—
the resistor can become hot.

3. Locate the Control Board. It is the circuit boar d clos­est to the front of the amplifier. It contains numerous
power supply connections which set the voltage and
one jumper block which sets the frequency.

4. Use the information in Figure 3.1 to connect the color­coded wiring harness correctly for the desired voltage.
Configure each wire group one at a time so the wires
are not confused. Do not mix wires between groups.
This step may require you to cut one or more tie wraps.
If you do, replace them to make sure no loose wires ar e
able to prevent the fans from rotating.

5. Locate the frequency jumper (JP1) and set it for ei­ther 60 Hz (left) or 50 Hz (right).

6. Locate the fan connector (P729/P730) and move it to
the appropriate voltage connector (left for 200-240 V AC
or right for 100-120 V AC).

7. Double check that all connections are correct and
replace the top cover.

* Wire colors marked with a single asterisk connect to the power cord.
** The connector numbers are listed in clockwise order from left to right

as you face the front of the amplifier.

*** Connection P729 and P730 are combined on a single four-pin connec-

tor. It mates to a “120V” connector for 100V or 120V operation or a
“240V” connector for 200, 208, 230 or 240 volts.

©2000 Crown International, Inc.

Voltage Conversion 3-1

MA-5002VZ Service Manual

130446-1 Rev. A

CAUTION: To reduce the risk of fire,
replace F700, F701, & F702 with the
same type fuse. Use a 30 A fuse for F700
& F701 and a 1A fuse for F701 for ALL
voltage configurations.

ATTENTION: Utiliser un fusible de même
type (F700, F701 = 30A. F702 = 1A.)
pour toutes applications.

3-2 Voltage Conversion

Figure 3.2 Voltage/Frequency Conversion Physical Layout

©2000 Crown International, Inc.

130446-1 Rev. A

4 Circuit Theory

4.1 Overview

It should be noted that over time Crown makes improve­ments and changes to their products for various rea­sons. This manual is up to date as of the time of writing.
For additional information regarding these amplifiers,
refer to the applicable Technical Notes provided by
Crown for this product. Sketches have been added to
this section for clarification of the various concepts pre­sented, as well as block diagrams for the amplifier and
specific portions of the amplifier . For detailed schemat­ics refer to Section 6.

MA-5002VZ Service Manual

is called Loudspeaker Offset Integration (LOI). The LOI
circuit, when switched on, prevents excessive bass fre­quency cone excursions below the audible frequency
range. It operates essentially as a band-pass filter . The
low frequencies are rolled off at 18 dB/octave with a
–3 dB corner of 35 Hz (Butterworth response). Ultra­sonics are rolled off with a second or der Bessel response
and –3 dB corner of 50 kHz.

A compression circuit in each channel may be switched
off, on slow, or on fast by switches on the rear panel.
This compressor is activated by either input overload
or distortion (clipping). Input overload compression is
in fast speed when the compressor switch is in the off
position. The compression ratio is infinite (it operates
as a peak limiter).

The Macro-Tech 5002VZ amplifier incorporates several
new technological advancements, including real-time
computer simulation of output transistor stress, low­stress output stages, an advanced heat diffuser em­bodiment, a programmable input processor (PIP) ex­pansion system, and articulated VZ power supplies.

Custom circuitry is incorporated to limit temperature and
current to safe levels—making it highly reliable and tol­erant of faults. Unlike many lesser amplifiers, the Macro­T ech 5002VZ can operate at its voltage and curr ent lim­its without self-destructing.

Real-time computer simulation is used to create an ana­log reading of the junction temperature of the output
transistors (herein referred to as the output devices).
Current is limited only when the device temperature be­comes excessive—and just by the minimum amount
necessary . This patented approach, called ODEP (Out­put Device Emulation Protection) maximizes the avail­able output power and eliminates overheating—the
major cause of device failure. ODEP in the MA-5002VZ
also provides indication of amplifier thermal reserve
(front panel ODEP indicators) and may provide contro l
of VZ mode when the VZ mode select switches are
placed in the VZ-ODEP position.

The amplifier is protected from all common hazards that
plague high-power amplifiers, including shorted, open
or mismatched loads, overloaded power supplies, ex­cessive temperature, chain-destruction phenomena,
input-overload damage, and high-frequency blowups.
The unit protects loudspeakers from DC in the input
signal and from turn-on and turn-off transients. It also
detects and prevents unwanted DC on the outputs.
Additional protection features include input voltage
sense as well as overvoltage (AC mains).

A mode of protection which may be switched on or off

The four-quadrant topology used in the grounded out­put stages is called the Grounded Bridge, and it makes
full use of the power supplies. This patented topology
also makes peak-to-peak voltages available to the load
which are twice the voltage any output device is ever
exposed to. The Grounded Bridge is covered in detail
in Section 4.2.

The two channels may be used together to double the
voltage (bridged-mono) or the current (parallel-mono)
presented to the load. This feature gives the user flex­ibility in maximizing the power available to the load.

Macro-T ech amplifiers utilize a wide bandwidth multiloop
feedback design with state of the art compensation tech­niques. This produces ideal behavior and results in ul­tra-low distortion values.

Aluminum extrusions have been widely used for
heatsinks in power amplifiers due to their low cost and
reasonable performance. However, measured on a
watts per pound or watts per volume basis, that extru­sion technology doesn’t perform nearly as well as the
cut fin radiator technology developed for the Macro­Tech 5002VZ power amplifier.

Our thermal diffusers are custom cut radiator fins on a
solid heat sink block. They provide an extremely high
ratio of area to volume, or area to weight. All power de­vices are mounted directly to massive heat spreaders,
which are electrically hot. Making the heat spreaders
electrically hot allows improved thermal performance
by eliminating the insulating interface underneath the
power devices. The chassis itself is used as part of the
thermal circuit, and this maximizes utilization of the avail­able resources.

4.2 Grounded Bridge Theory

The Grounded Bridge topology is ground-referenced

©2000 Crown International, Inc.

Circuit Theory 4-1

MA-5002VZ Service Manual

130446-1 Rev. A

Figure 4.1 Simplified Grounded Bridge

by the output stages rather than the power supply.
Composite devices are constructed to function as gi­gantic NPN and PNP devices since the available cur­rents exceed the limits of existing individual devices.

The devices connected to the load are referred to as
“high-side NPN and PNP” and the devices connected
to ground are referred to as “low-side NPN and PNP.”
Positive voltage is delivered to the load by increasing
conductance simultaneously in the high-side NPN and
low-side PNP stage. At the same time, conductance of
the high-side PNP and low-side NPN is being de­creased.

4.2.1 Grounded Bridge Operation

Figure 4.1 is a simplified example of Crown’s patented
Grounded Bridge output topology (ignoring the articu­lating characteristics of the VZ supply). It consists of
four quadrants of three-deep Darlington (composite)
emitter-follower stages per channel: one NPN and one
PNP on the high side of the bridge (driving the load),
and one NPN and one PNP on the low side of the bridge
(controlling the ground refer ence for the rails). The out­put stages are biased to operate class AB+B for ultra
low distortion in the signal cross-over region.

The high side of the bridge operates similar to a con­ventional bipolar push-pull output configuration. As the
input drive voltage becomes more positive, the high side
NPN conducts current and delivers positive voltage to
the speaker load. Eventually , full +Vcc is across the load.
At this time the high side PNP is biased off. When the
drive signal is negative going, the high side PNP con-

ducts to deliver –Vcc to the load and the high side NPN
stage is off.

The low side operates quite differently. The power sup­ply bridge rectifier is not ground referenced. This al­lows the power supply to deliver +Vcc and –Vcc from
the same bridge rectifier and filter as a total difference
in potential, regardless of their voltages with respect to
ground. The low side of bridge uses inverted feedback
from the high side output to control the ground refer­ence for the rails.

As the output swings positive, the output signal is fed
back to the low side and is inverted to drive the low
side with a negative signal. The negative signal causes
the low side PNP to conduct (as the high side NPN con­ducts) shifting the ground reference toward –Vcc until,
at the peak, –Vcc = 0V. At this time +Vcc equals the full
potential (from rail to rail, not rail to ground) of the power
supply with positive polarity. Since the high side is de­livering +Vcc to the speaker load (which is ground ref­erenced at all times), the speaker sees the full potential
developed by the power supply with a positive polarity .

When the input drive signal is negative and the high
side PNP conducts to deliver a negative voltage to the
load, that output is again fed to the low side and in­verted to cause the low side NPN to conduct. As the
low side NPN conducts, +Vcc swings toward the 0V
ground potential. At the peak: +Vcc = 0V. At this time
–Vcc equals the full potential developed by the power
supply , but with negative polarity. Since the high side is
delivering –Vcc to the speaker load, the load sees the

4-2 Circuit Theory

©2000 Crown International, Inc.

130446-1 Rev. A

MA-5002VZ Service Manual

full (negative) potential developed by the power sup­ply.

The total effect is to deliver a peak to peak voltage to
the speaker load which is twice the (static) voltage pro­duced by the power supply . Benefits include full utiliza­tion of the power supply (it conducts current during both
halves of the output signal; conventional designs re­quire two power supplies per channel, one positive and
one negative), and never exposing any output device
to more than half of the peak to peak output voltage
(which does occur in conventional designs).

4.2.2 Output Stage Circuitry

Circuitry on the positive and negative output modules
include bias circuitry, current limit circuitry, last voltage
amplifiers (LVAs), pre-drivers, drivers, output devices,
and the Low Side error amp. Temperature sensors are
also mounted to the heatsinks via the output modules.

The positive L VAs (Q501, Q502, and Q503) convert the
negative output of the voltage translator stage to a posi­tive drive voltage for the NPN High Side (HS) predriver.
There are three LVA transistors in parallel due to the
very high voltages (therefore higher current and ther­mal requirements) that are present when the power
supply is in high voltage mode. D522 prevents the +L V As
from producing a high negative output to the HS NPN
stage.

Q507, Q508, and Q509 are the -LV As and are arranged
in mirror image to the +LVAs, including D513.

On the positive side, D514, D515, and C506 via the
+LVAs act to limit slew rate. D514 and D515 also pre­vent dangerously excessive current through the LVAs.
D516, D517, and C507 are the negative HS mirror im­age.

Q534 and Q540 provide two-speed current limiting in
the output stage. Sense lines are arranged such that
excessive current through any single HS output device
will result in current limit protection. Q535 and Q541 ar e
the negative side mirror image.

Q505 on the positive output module works in tandem
with Q505 on the negative output module as a Vbe
multiplier circuit. They produce and, with great stability,
control bias for the High Side NPN and PNP devices.
Potentiometer R505 is used to precisely set bias volt­age. Bias voltage is easily measured from pin 2 (hot) to
pin 4 of ATE ports TP1 and TP2. Refer to Section 2 for
appropriate test procedures.

Q504 is the HS NPN pre-driver and Q511 is the HS
NPN driver. These devices are biased class AB for ul­tra low distortion in the zero-crossing region.

Q513, Q515, Q517, and Q536 are the HS NPN output
devices. These devices are biased class B, in soft cut­off. Together with driver and pre-driver, they function as
a three-deep Darlington. The output devices work in
parallel as a giant composite. The over-all bias topol­ogy is referred to as AB+B, originally conceived and
patented by Crown engineers in 1966. This is still the
most efficient, stable, and distortion free method used
today in BJT output stages.

D506 is the flyback diode for the HS NPN output quad­rant. In the event that a back EMF (flyback) pulse ex­ceeds power supply voltage, the flyback diode will shunt
this voltage to the supply in order to protect the output
devices.

PNP pre-drivers, drivers, output devices, and flyback
diode D508 are a mirror image of the NPN side.

Overall, the High Side of the bridge operates much like
a conventional output stage, but the Low Side (LS) is
quite unique.

The LS senses output voltage and common buss (0.04
ohms above ground) potential. The audio output is in­verted by U503. Also in the U503 input circuitry are static
and dynamic balance controls. These controls provide
a fine balance of the grounded bridge. Output of the
op-amp drives the LS pre-driver circuits through the LS
bias network.

LS bias is controlled in a fashion similar to that of the
HS. Two transistors, Q529 and Q530, fix LS bias volt­age as measured from pin 15 (hot) to pin 13 of appli­cable A TE port TP1 or TP2. Potentiometer R556 adjusts
bias in the LS.

Diodes D504 and D505 control polarity of applied LS
drive signal. Via the bias transistors, signal is delivered
to the bases of the pre-drivers Q527 (NPN) and Q528
(PNP). Pre-drivers, drivers, and output devices in the
LS operate class AB+B, exactly like the HS. The major
difference is that rather than driving a load, the NPN
and PNP stages control the ground reference for the
high voltage rails. As the HS NPNs conduct, LS PNPs
conduct, and vice versa (as explained in section 4.2.1).

When the ODEP circuit senses that limiting drive is nec­essary to prevent a dangerous thermal condition, it pro­vides an output which limits drive to the output stages.
For the HS, this limiting is accomplished on the main
module and is explained in section 4.4. For the LS, ODEP
provides (via wires labeled ±LL) a signal which limits
bias feed to the LS output devices. This is accomplished
through current mirrors Q532 and Q531 (LS NPN quad­rant), and Q542 and Q543 (LS PNP quadrant).

©2000 Crown International, Inc.

Circuit Theory 4-3

MA-5002VZ Service Manual

130446-1 Rev. A

4.3 VZ Power Supply

VZ means Variable Impedance and is the name of
Crown’ s patented articulated power supply technology .
It enables Crown to pack tremendous power into just

5.25 inches of vertical rack space.
A power supply must be large enough to handle the

maximum voltage and current necessary for the ampli­fier to drive its maximum rated power into a specified
load. In the process of fulfilling this requirement, con­ventional power supply designs produce lots of heat,
are heavy, and take up precious real estate. And it’s no
secret that heat is one of a power amplifiers worst en­emies.

According to Ohm’s Law, the bigger the power supply,
the more heat the power transistors must dissipate. Also,
the lower the resistance of the power transistors, the
more voltage you can deliver to the load. But at the
same time that you lower the resistance of the transis­tors, you increase the current passing through them,
and again increase the amount of heat they must dissi­pate.

4.3.1 VZ Supply Operation

An articulated power supply, like VZ, can circumvent
much of this problem by reducing the voltage applied
to the transistors when less voltage is required. Reduc­ing the voltage reduces the heat. Since the amplifier
runs cooler, you can safely pack more power into the
chassis.

Toroid

Bridge 1

–

Bridge 2

+VCC Buss

+

HI IHI V

(MOSFETs)

+–

The VZ supply is divided into segments to better match
the voltage and current requirements of the power tran­sistors. Remember that audio signals like music are
complex waveforms. Refer to Figures 4.2 and 4.3.

For music the average level is always much less than
the peak level. This means a power supply does not
need to produce full voltage all the time.

The VZ supply is divided into two parts. When the volt­age requirements are not high, it operates in a parallel
mode to produce less voltage and more current.

The power transistors stay cooler and are not forced to
needlessly dissipate heat. This is the normal operating
mode of the VZ power supply.

When the voltage requirements are high, VZ switches
to a series mode to produce higher voltage and less
current. The amplified output signal never misses a beat
and gets full voltage only when it needs it.

Sensing circuitry watches the voltage of the output sig­nal to determine when to switch VZ modes. The switch­ing circuitry is designed to prevent audible switching
distortion to yield the highest dynamic transfer function
— you hear only the music and not the amplifier. You
get not only the maximum power with the maximum
safety, you also get the best power matching to your
load.

In Figure 4.2, the individual components are

shown. Upstream of the toroid transformer,
though not shown, is where shutdown protec­tion and soft-start circuitry taps in to control AC
mains input to the power supply. The VZ Control
circuitry senses audio level and switches the ar­ticulating VZ supplies to either parallel (high cur ­rent) mode for lower level audio, or series (high

D 810

voltage) mode for high program peaks.
Figure 4.3 shows current flow with power supply

and grounded bridge operating to­gether . Notice that the ungrounded

VZ Control

Circuitry

VZ supply operates much like a
battery . More exactly, it is a float­ing DC supply made up of two in­ternal batteries which operate in
either series or parallel.

Figure 4.2 Simplified VZ Supply

4-4 Circuit Theory

D 811

-VCC Buss

In both examples it can be seen that when the
MOSFET switch is off, the dual supplies are
forced to operate in a parallel mode. Audio level
is sensed via a line tapping off the NFb loop.

When audio level is rising and at about 80% of
the parallel mode supply voltage, the MOSFET s
(the switch is actually a three-device compos-

©2000 Crown International, Inc.

130446-1 Rev. A

VZ Power Supply Grounded Bridge Output Topology&

MA-5002VZ Service Manual

+

R

+

V

1

(+Vcc)

+Vcc (Positive Rail)

R

Input
signal

S1

(-V

–

+

V

2

––

HIGH SIDE LOW SIDE

Parallel =
Series =

)

cc

R = Switch Resistance

Load

(speaker)

-Vcc (Negative Rail)

Inverting Op-amp

Figure 4.3 Simplified VZ Supply in Operation

ite switch) are turned on. No current will flow through
either of the control diodes (D810 and D811, as shown
for channel 1) because reverse polarity is applied
through the MOSFET switch. Since this happens to both
rectifier sources at the same time, and the negative side
of Bridge 1 is then shorted to the positive side of Bridge
2, the supplies are forced to operate in series mode.
Like two batteries, the supplies will provide double volt­age in series mode, double current in parallel mode.

Although shipped from the factory in VZ-ODEP mode,
the user may switch modes to Lock Low voltage (high
current), or operate the supply in VZ-AUTO mode. VZ­ODEP is similar to VZ-AUTO mode, except that in AUTO
mode, in the event ODEP is activated to protect the
amplifier, the VZ will automatically lock into low voltage
(high current) mode. While this mode of operation will
cool the amplifier more quickly in the event that the ther ­mal reserve is exhausted, it may cause voltage clip­ping rather than ODEP limiting. Seldom will the ampli­fier be operated locked in high current mode unless a
very low impedance is being driven.

4.3.2 VZ Supply Circuitry

For simplicity, only channel 1 circuitry will be covered
unless noted otherwise. The actual VZ switch circuit is
located on the VZ switch assembly . This assembly con­tains the filter capacitors, MOSFET switches, and con­trol diodes (D810 and D811). Three MOSFETs are used
in parallel for sharing the high current supplied to the
rails. Operation of this section was covered in detail,
minus circuit designations, in Section 4.3.1.

WARNING: From a service standpoint, it is critical
to note that VZ switch control cir cuitry is NOT gr ound
referenced. Any attempt to take voltage measure­ments using a ground reference when voltage is
applied will not only be unreliable, but may be ex­tremely dangerous. Serious damag e to equipment
or personnel may occur if this is attempted.

The output of a 555 timer (U703) on the control module
determines whether the MOSFETs are switched on
(high) or off (low). This 555 device and the various
sources that feed the 555 are the things that make the
articulation work.

The master 555 trigger is controlled by the output of

©2000 Crown International, Inc.

Circuit Theory 4-5

MA-5002VZ Service Manual

130446-1 Rev. A

U702A. S700, physically accessible from behind the
front grille, determines the VZ operating mode. In high
voltage mode (Q42930-0 Control Module only) the out­put of U702A is held low. This in turn keeps the 555
output high and the MOSFETs are kept on. In the high
current mode, U702A is held in the opposite polarity,
keeping the output of the 555 low and the MOSFET s of f.
In the AUTO position of S700, the audio level sense
circuitry controls the threshold and reset inputs to the

555. The 555 will then switch states to high voltage when
the audio level is sufficient and will switch back down
automatically when level has dropped sufficiently. Ca­pacitors in the U705 circuitry control the speed of the
down-shift. In the VZ-ODEP mode, the switch operates
as it would in AUTO mode unless ODEP limiting is in
progress. When ODEP limiting occurs, optic coupler
U704 pulls the reset control low to the 555 to turn the
MOSFET switches off, and keep them off (low voltage/
high current mode) until the ODEP limiting condition
clears.

Upstream of the toroids are the soft-star t and protec­tion mechanisms used to power down the amplifier.
Although tied into the power supply primary, these cir­cuits are covered in Section 4.6, Protection Systems.

The low voltage power supply utilizes a separate trans­former. The front panel power switch and a 1A fuse
(F702) are the only components upstream of this trans­former. The output of the rectifier produces ±24VDC
unregulated. U715 and U716 produce regulated
±15VDC respectively . (A separate fullwave rectifier pr o­duces pulsed DC for Over-voltage sense and Soft-start
control.)

4.4 ODEP Theory

To protect the output stages from adverse thermal con­ditions, a specially developed “ODEP” (Output Device
Emulator Protection) circuit is used. It produces a com­plex analog output signal proportional to the always
changing safe-operating-area (SOA) margin of the out­put transistors. This output signal controls the Voltage
Translator stage and Low Side output stage bias. This
action removes only the drive that may exceed the safe­operating-area of the output stage.

Thermal sensors give the ODEP circuitry vital informa­tion on the operating temperature of the heat sinks on
which the output devices are mounted. This tempera­ture signal combines with the complex ODEP signal to
form the heart of our patented ODEP protection scheme.

4.4.1 ODEP Operation

Refer to Figure 4.4 for a diagram of the basic operation
of the ODEP system.

The ODEP circuitry actually comes in two parts, one
positive and the other negative. For the purposes of
this discussion, only the channel 1 ODEP circuitry is
covered here, and the focus will primarily be on the
positive half.

An LM-334Z thermal sensor provides a calibrated out­put from the output modules. At 25°C its output is 2.98V,
with a 10 mV increase per every 1°C rise in heatsink
temperature.

This thermal sensor output, from the positive sensor,
goes to three destinations. First is a buffer which drives
the calibrated temperature test point at pin 7 of TP1/
TP2. Second is an over-temperature limit trip (thermal
limit amplifier, as shown below). This will cause both
the positive and the negative ODEP circuit to go into,
and remain in, hard ODEP until the heatsinks cool. Third,
it goes down into a circuit which combines thermal and
output power information.

The thermal sensor from the negative output module
only performs this last function.

A pair of sense lines from the Low Side emitter resistors
provide current information. Combined with VCC infor ­mation, actual instantaneous power is calculated. A
combining circuit determines the net thermal condition
based on the power being delivered for the existing
heat level. The ODEP amplifier accepts this input infor ­mation and, using an RC model of the heat transfer
characteristics of the output devices (as mounted in
the heatsinks), creates a complex output proportional
to the thermal reserve of the output devices.

Output from the positive ODEP amplifier ranges from
–12V (cold) to +9V (hard ODEP). This output drives the
positive LS bias feed control circuit (see Section 4.2.2)
and the negative HS Voltage Translator feed control cir­cuit (see Section 4.5.2). Also, this circuit provides test
point monitoring information and VZ-ODEP VZ mode
control information.

Output from the negative ODEP amplifier ranges from
+12V (cold) to –9V (hard ODEP). This output drives the
negative LS bias feed control circuit (see Section 4.2.2)
and the positive HS V oltage Translator feed control cir­cuit (see Section 4.5.2). Also, this circuit provides test
point monitoring information, VZ-ODEP control informa­tion, and front panel ODEP (thermal reserve) LED con­trol information.

Also tapping into the ODEP output control of LS bias
feed and Voltage Translator feed are signals from the
fault, power (turn-on delay), and power loss (brown­out) circuits. By using the output of ODEP for ±LL and
±LH control, these sources can mute the audio to the

4-6 Circuit Theory

©2000 Crown International, Inc.

130446-1 Rev. A

MA-5002VZ Service Manual

Channel 1 ODEP Circuitry shown

ODEP Inputs:
Temperature
±VCC
Output Current

Module

LM-334Z

Thermal Sensor

(+2.98V at 25˚C,

+10mV/˚C Rise)

+VCC

Q519 LS
Output

R

e

Common Output Buss

R

e

Q524 LS
Output

-VCC

LM-334Z

Thermal Sensor

+Temp 1

+VCC

+IC 1

+ICOM 1

-ICOM 1

-IC 1

-VCC

-Temp 1

ODEP Outputs:
Calibrated Temperature, for monitoring
±ODEP Level, for monitoring
±ODEP Level, for Bi-ODEP control of VZ Supply
±ODEP Level, to limit drive at ±Voltage Translators (±LH)
±ODEP Level, to limit Low Side Bias (±LL)
ODEP Indication (front panel LEDs)

On Main ModuleOff Main

Calibrated Temperature Output

Buffer Amplifier
Thermal Limit Amplifier

+ODEP Amplifier

RC Network

Thermal Model

-ODEP Amplifier

RC Network

Thermal Model

Cold

-12V

+12V

Cold

Hot

Hot

+9V

+ODEP Output

-LH 1

+LL 1

FAULT 1
PWR 1
PWR LOSS

+LH 1

-LL 1

-ODEP Output

-9V

Figure 4.4 Simplified ODEP Circuitry

output stage: a. until power -up delay has timed out; b.
immediately upon indication of any failure mode; c. im­mediately upon loss of AC mains (power-down or ac­tual loss of AC service).

4.4.2 ODEP Circuitry

±TEMP signals are produced by U500 and U501 on
the output modules. U108, on the main module, is a
buffer which drives the temperature sense test point.
U117A has a fixed window voltage of 6.2V via Zener
D129. If heatsink temperature level exceeds about
130°C, U117A output will cause both the positive and
negative ODEP amplifiers to go into hard ODEP limit-

©2000 Crown International, Inc.

ing. When the thermal condition clears, this limiting con­dition will also clear.

+VCC enters via dual PNP transistor pack U116.
Positive ODEP bias is adjusted by R182. The voltage at
that point controls the static balance of the U116 de­vice. U116 combines the VCC and output current sense
information, the output of which represents output power
level. The common output is brought into RN101 where
it provides the reference for temperature and power.
U112B is the active device and, together with the power
signal, drives the ODEP amplifier U112A. The RC net­work in the feedback path of U112A models the ther­mal junctions from output device die to housing, hous-

Circuit Theory 4-7

MA-5002VZ Service Manual

130446-1 Rev. A

ing to case, and case to heatsink under both static and
dynamic conditions.

The output of the positive ODEP amplifier drives +ODEP
test point pin 11. It also drives U114A and U114B which
in turn drive – LH and +LL respectively. The output of
the negative ODEP amplifier drives the ODEP indica­tion circuitry and –ODEP test point pin 9. Negative ODEP
also drives U114C and U114D which in turn drive +LH
and – LL respectively.

Also entering the U114 comparator networks are the
PWR (power relay engage), PWRLOSS (brown-out), and
FAULT (any protection which shuts down the amplifier)
signals via blocking diodes. If any of these signals drop
low, the feed to the LS bias and V oltage Translator drive
will be shut down via ±LL and ±LH. This action mutes
all audio in the event of a dramatic failure.

4.5 Front End Theory

Figure 4.5 explodes the front-end portion of the overall
block diagram. Once again, only channel 1 will be dis­cussed in detail.

Input to the amplifier is only via a PIP module. The stan­dard module shipped with the MA-5002VZ is the PIP2­FXQ. Whether this, or any other module is used, the
amplifier senses a balanced input from the installed
module.

4.5.1 Balanced Gain Stage

The Balanced Gain Stage (BGS) amplifier U100A con­verts the input audio from a balanced configuration to
single-ended with (electrical) unity gain. The compres­sion device is essentially a resistive shunt across the
balanced BGS input. The BGS drives the V ariable Gain
Stage and provides information to the compressor con­trol circuit and to the PIP connector.

4.5.2 Variable Gain Stage

The Variable Gain Stage (U100B) taps signal from the
wiper of the front panel level control (R120). Gain of the
front-end is set by the gain of this stage. The sensitivity
switch (S100, located on the rear panel) selects the
amount of gain in this stage. Overall amplifier sensitivity
may be set for 26 dB fixed gain (about 5.1Vrms), 1.4V,
or 0.775V. Since overall amplifier gain after this stage is
26 dB, this stage will have a fixed gain of 0 dB (26 dB
setting), about +12 dB (1.4V setting), or about +16 dB
(0.775V setting). The output of this stage drives the Er ­ror Amp.

4.5.3 Error Amp

The Error Amp (U105) input comes from the Variable
Gain Stage with or without Loudspeaker Offset Integra­tion (LOI), and is summed with amplifier output in a nega­tive feedback (NFb) configuration. Output of the Error
Amp drives the Voltage Translators and provides error

4-8 Circuit Theory

Figure 4.5 Front End Circuitry Block Diagram

©2000 Crown International, Inc.

130446-1 Rev. A

MA-5002VZ Service Manual

signal information. An error signal (spike) is produced
any time the shape of the output waveform differs from
the output of the Variable Gain Stage and LOI by mor e
than 0.05%. This error signal drives the error signal (ES)
input to the PIP connector, the error signal sense test
point, and the compression control circuit.

4.5.4 Compressor

The compression circuitry senses error signal and BGS
level. If the BGS overloads, or an error signal is present,
the compression control circuit (U101) pr oduces a com­pression drive pulse. A switch on the rear panel selects
the speed of the integrator circuit to follow. In the off
position, the error driven compression is disabled, but
the input overload compression remains on (in fast
speed) to protect the front end. The compression drive
pulse also drives the IOC Integrator (U102). The IOC
integrator not only tells the IOC indicator circuit when to
turn on, but ensures that the indicator will remain on
long enough to be visible to the human eye.

The compression integrator (U102, Q100) sets com­pression speed and produces an output pulse which
controls attack and decay times. An optic device (U103)
provides a resistive shunt to the input audio according
to the degree of compression required and the dura­tion of that compression. The amplifier input impedance
is not affected by compressor operation.

4.5.7 Inverting Stages

Overall, the amplifier is non-inverting. Four stages within
the amplifier, however, do inver t the audio signal for a
net non-inversion. The individual stages are: the BGS,
which inverts the audio; the Variable Gain Stage, which
inverts it back; the input side of U106 and U107 (which
drives the V oltage Translators) re-inverts the audio (the
Voltage Translators are a common-base configuration
for high voltage gain); and finally, the LVAs invert the
audio for the last time for a net non-inversion through
the amplifier.

4.6 Protection Systems

The MA-5002VZ has several protection mechanisms to
limit drive or shutdown the amplifier completely in the
event of a fault of almost any kind. Mechanisms include:
ODEP (covered in depth in Section 4.4), current limit
(covered in Section 4.2.2), over -voltage (on AC mains),
DC/LFI, common mode output current, output thermal,
transformer thermal, FET thermal, loss of AC mains,
compression (covered in Section 4.5.4), LOI (covered
in Section 4.5.5), and slew rate limit (covered in Section

4.2.2). After any non-latching fault which has shut down
the amplifier clears, the amplifier will automatically power
back up via soft-start. Because the fans within the MA­5002VZ cool the amplifier (under normal conditions) to
prevent thermal shutdowns and ODEP limiting, the fan
control circuit is also covered in this section.

4.5.5 Loudspeaker Offset Integration

LOI (U104A/B) senses amplifier feedback and prevents
dynamic DC offset. It operates essentially as a dual fil­ter system with band pass from about 35 Hz to about
50 kHz. The upper roll-off has a second order Bessel
response while the lower roll-off has a third order
Butterworth response.

4.5.6 Voltage Translator and LVA Stages

The Voltage Translator stages (Q104, Q104) channel
the signal to the Last Voltage Amplifiers (LVAs, located
on the output modules), depending on the signal polar ­ity , from the error amp U105. The ±LVAs, with their push­pull effect through the High Side bias servo devices,
drive the fully complementary output stage. For more
information on the LVAs, refer to Section 4.2.

U106 and U107 bring in feedback information and pro­tection muting to the V oltage T ranslator stages. The feed­back controls gain from the Voltage Translators to the
output jacks. The protection inputs (±LH) pull off feed
to the Voltage Translators in proportion to ODEP limit­ing, and completely shut down the feed in the event of
power-down or a Fault.

Refer to Figures 4.6, 4.7, and 4.8. Figure 4.6 shows soft­start and fan control. Figure 4.7 shows the soft-start con­trol signals. Figure 4.8 shows the over-all protection
scheme of the MA-5002VZ. Each augments the others,
and explode the basic block diagram of the unit (Fig­ure 4.9).

4.6.1 Soft-start

Soft-start circuitry controls the rate at which power is
initially applied to the primary of the toroid transformers
for the high-voltage power supplies. For ease of expla­nation, assume the amplifier is operating properly and
is just being turned on from the front panel power switch.

Before the power switch push-button is depressed, the
input to the low voltage supply is open. The high volt­age supply is isolated via input relay K700 and triac
Q701 (which is in parallel with K700).

Several things occur immediately at turn-on. First, the
low voltage supply powers up and produces its main
unregulated ±24VDC and regulated ±15VDC. It also
immediately produces pulsed DC via full-wave rectifier
D709/D714.

©2000 Crown International, Inc.

Circuit Theory 4-9

MA-5002VZ Service Manual

Portion of

Main Module

+15V

+10.4V

POWER

ON

-

+

RELAY

DRIVE

130446-1 Rev. A

POWER

XFMR

RELAY

K700

OV/TSW

PWRLOSS

POWER
SWITCH

LOW

VOLTAGE

POWER

SUPPLY

FANS

FAULT
DC/LFI

VOLTAGE

DIVIDER

WITH C120

-15V

+15V

-15V

+24V

-24V
FAN

DRIVERS

STANDBY

DRIVER

DC PULSE

WIDTH

CONTROL

+

-

TSW1

TSW2

SOFT-START

DRIVER

­+

TO CH 2 SOFT-START DRIVER

CH 1 FAN

CONTROL

CH 2 FAN

CONTROL

POSITOR

5.0 OHM

TEMPERATURE CH 1

ODEP CH 1

TEMPERATURE CH 2

ODEP CH 2

Figure 4.6 Soft-start and Fan Control

As this occurs, all op-amps in the amplifier receive
power, including front-end stages, relay power control
U111C, and standby control U111B. The output of
U111C powers relay K700 via relay drive transistor
Q700. When the output of this op-amp goes high, Q700
turns on and the relay closes. The output of U111C is
held low until the amplifier delay times out by compar­ing a high voltage on its inverting input to an RC net­work voltage on its non-inverting input. R329 and R330
fix a window at about +10.4VDC. At turn-on, C220 (a
10 µF cap) is fully discharged. In that first instant, it keeps
–15V on the non-inverting input of U111C, keeping its
output low. As the capacitor charges it produces a
ramped rise in voltage as it charges through R327. Af­ter about 4 seconds, the voltage between R327 and
R328 exceeds the window voltage and U111C output
goes high, in turn causing relay K700 to close.

4-10 Circuit Theory

Note: Any protection signal within the amplifier which is
used to shut it down will discharge this capacitor (C120),
immediately causing the relay (K700) to open. Upon
clearance of such a shut-down protection signal, the
charge will begin again with the same ramp effect and
same delay.

The ramped voltage on the capacitor C120 is also
sensed by Standby amplifier U111B. Its unity gain out­put is non-inverting. It drives the Soft-start op-amp
(U701A) inverting input with its ramp to control the rate
at which the field develops in the toroid. On the non­inverting input to U701A is the pulsed DC drive from
the U701B/Q708 pulse circuit. Jumper JP1 may be set
to 50 or 60 Hz, but must be set properly to have the
correct pulse width for soft-start. Pulse width is deter­mined by C717 and either R777 (50 Hz) or R777 in par ­allel with R806 (60 Hz).

©2000 Crown International, Inc.

130446-1 Rev. A

MA-5002VZ Service Manual

The output of U701A controls the Soft-start. Refer to
Figure 4.6 for a graphic of Soft-start operation.

When the output of U701A goes low, the opto-triac de­vice U700 turns on. While on, the input triac Q700 con­ducts. Positor R702 limits peak input current to the tor­oid to a maximum of 22A peak (with 120VAC mains).
U701A combines the sloped input from the C120 cir­cuitry on the main module with the pulsed DC. As the
portion of time which the output of U701A goes low in­creases, the amount of time where AC mains conduct
to the transformer (via Q700 and R702) increases until
it remains on. When the U111C PWR circuit times out,
the relay closes, bypassing the current limiting soft-start
circuit. Soft-start control signals are shown in Figure 4.7.
The upper signal is that produced by C120. At time 0
the amplifier is off. At time 1 the power switch is pressed
(on). At time 2 C120 has fully charged, the magnetic

C120

CHARGE

VOLTAGE

01 2 3 4 5 6

fields have built up in the high voltage supply, and the
main relay closes. At time 3 a protective action occurs;
note that the DC supply remains. At time 4 the condi­tion clears and the restart begins. Time 5 is akin to time
2, and time 6 is another protective action. The lower
graph shows Q701 operation (high = on).

Any time a protection mechanism has acted and the
condition then clears, this entire process repeats.

4.6.2 Over-voltage

One mode of amplifier protection is a shutdown in the
event of over-voltage on the AC mains. This is sensed
by the pulsed DC signal produced by the full-wave rec­tifier in the low voltage supply.

R780 picks off the pulsed DC, and U707D will, if the
voltage is too high, shift its output to a low. When this
happens, the over-volt/therm red LED on the control

module lights and signal OV1 goes low

to the main module.

A low (over-voltage condition) on

OV1 causes U211C to shift to a
low output. This low , through D1,
causes C120 to discharge im­mediately . This in turn causes the
main relay to drop out, soft-start
to reset, and the ±LL and ±LH
to clamp audio drive. Over-volt­age is a non-latching fault con­dition.

PULSED

DC FROM

LVPS

01 2 3 4 5 6

SOFT-START

TRIAC

CONTROL

01 2 3 4 5 6

©2000 Crown International, Inc.

Figure 4.7 Soft-start Signal

4.6.3 DC/LF

The amplifier senses its own out­put for DC or very low frequency
and will interrupt the amplifier
channel in the event of DC or low
frequency.

The feedback loop is sensed for
voltage and the current sense
signal provides current informa­tion. An RC network at the input
to U109C/D will prevent the LF
circuit from activating with nor­mal audio frequency material,
and will ensure activation with
high level subsonic currents or
voltages.

If U109C/D sense a DC (or LF)
level, it will output a low, which
will, through D102, discharge
C120 and initiate power supply

Circuit Theory 4-11

MA-5002VZ Service Manual

130446-1 Rev. A

shutdown. A low will also cause the DC/LF red LED on
the main module to light. DC/LF is a non-latching pro­tection mechanism.

4.6.4 Common Mode Output Current

Common mode current in the output stage
can only be due to an output stage failure
or full power output of RF energy. Com­mon mode current occurs when a high
current level exists in both the positive and
the negative halves of the output stage.

U115 is a specialty device. It serves as
both an Opto-SCR, and as a conventional
SCR. It must have both an optic gate and
conventional gate firing at the same time
in order to latch. The conventional gate is
fired by current sense of the output stage
Low-side. The optic gate is fired by the
High-side current sense. If high currents
exist in both sides simultaneously , the SCR
will latch on, and remain on until the unit is
turned off.

When the SCR latches, low voltage causes
the red LED (labeled Output Module) to
light, and places a low on the FAULT sig­nal line. A low on the F AUL T line is sensed,
via D112, by C120. Once again, a low here
discharges C120 and shuts down the am­plifier. FAULT is a latching protection
mechanism (the only one in the amplifier).

V

01

C120

4.6.5 Output Thermal

Output over-temperature protection has
been covered, to a degree, in Section

4.4.2, ODEP Circuitry . The calibrated tem­perature sense from the positive half of the
output stage drives an over-temperature
amp, U117A. If heatsink temperature ex­ceeds a limit of about 130°C, the amplifier
will go into hard ODEP. This does not shut
down the amplifier , but does clamp the au­dio. Refer to Section 4.4.2.

4.6.6 Transformer Thermal

The main power transformers have built-in thermal
switches which open in the event of transformer over­temperature. In the event that the thermal switch opens
in the channel 1 toroid, Q709 turns on, causing U707D
to go low. When it does, the over -voltage/thermal switch
LED on the control module is energized and the OV1
signal is tripped; the fans are also forced to high speed.
Transformer thermal protection is self-resetting. This

DC PULSE

WIDTH

+15V

-15V

DC/LF

RED

OUTPUT

MODULE

RED

PWR LOSS

x1 BUFFER

STBY

RED

+10.4V

OV/TSW

CONTROL

-

+

DC/LF

FAULT

OV/TSW

RED

STANDBY

PWR

To Ch 2

+

-

CURRENT SENSE

±15VDC

OVER-VOLTAGE

TOROID

THERMAL

SWITCH

REMOTE
STANDBY
FROM PIP

SOFT-START

CONTROL

+

-

DC VOLTAGE &

FAULT

SENSE

SENSE

To Ch 2

FOR LS BIAS &

V XLTR FEED

LS NPN CURRENT
HS NPN CURRENT

Figure 4.8 Over-all Protection Scheme

results in amplifier shutdown by way of shared over­voltage circuitry. Refer to Section 4.6.2.

4.6.7 FET Thermal

A special circuit has been designed into the MA-5002VZ
to protect the MOSFET switches in the VZ supply. The
voltage drop across the FETs (while conducting) is pro­portional to device temperature. Control circuitry senses
the voltage and, if necessary , the supply will be for ced
into low voltage (high current) mode to allow the FET
devices to cool.

SOFT­START

MAIN

RELAY

±LL & ±LH

CONTROL

4-12 Circuit Theory

©2000 Crown International, Inc.

130446-1 Rev. A

MA-5002VZ Service Manual

4.6.8 Power Loss

The MA-5002VZ has the ability to sense a “brown-out”
condition on the AC service. This is accomplished by
sensing the low-voltage power supply at U111A. Local
capacitors on the ±15VDC keep this chip powered for
a short time after the low voltage supply drops out on
power-down/loss.

An RC network, consisting of C1 and R6, will cause the
output of U111A to shift low the instant low voltage is
lost. This negative potential discharges C120 causing
immediate opening of the main relay, and reset of the
Soft-start circuitry . It is essential that C120 be discharged
immediately in the event that power is restored before
C120 would otherwise discharge. The power-loss cir­cuit is common to both channels. Its output goes to
±LL and ±LH to immediately mute audio upon power­down or power-loss, thus pr eventing turn-off audio noise.

4.6.9 Fan Control

The MA-5002VZ, unlike other members of the Macro­Tech family, has two onboard fans. They are mounted
to the chassis divider assembly and pull cool air from
the front and discharge it across the output stage
heatsinks to the rear of the amplifier . Also unlike the other
Macro-T echs, the fans are fully ODEP pr oportional (they
operate in proportion to output stage temperature and
calibrated ODEP control voltage).

U713B combines channel 1 temperature and ODEP
level, U713A for channel 2. D706 and D707 form a di­ode OR gate. The output of the OR gate drives one
input to U707B. The other input to U707B is from the
DC pulse width control circuit (U701B). U707B oper­ates in a fashion similar to that of U707A, the Soft-start
control amplifier. A graphic example of the fan control
waveforms would look a good deal like those in Figure

4.7, except that the thermal drive would be unique from
that of the Soft-start ramp.

The fans will also be forced to operate at full speed in
the event a toroid transformer thermal switch trips open.

4.7 Display

Amplifier front panel indication includes a total of 7 LEDs.
These include Enable, ODEP, SPI/IOC, and ILOAD/ILIMIT.

fier thermal reserve. The LEDs are amber (although they
may have a reddish appearance) and are normally on.
They dim and/or extinguish in the event that the
amplifier’s thermal r eserve is exhausted. ODEP indica­tors will also extinguish whenever the main supply re­lays are open (such as a protection action being acti­vated, or during Soft-start time-out).

Green SPI/IOC LEDs show signal presence (SPI) and
any form of distortion (IOC). They flash dimly with the
audio to show signal. In the event of an IOC condition
(output waveform differs from input by >0.05%, or input
overload) the light will be on brightly . An occasional flash
of IOC usually indicates clipping. If the IOC light locks
in, it usually indicates a protective action, or “har d” ODEP
limiting.

ILOAD/ILIMIT LEDs flash green with the audio when pro­gram material is being delivered to a load. Its function
is similar to that of the SPI, except that SPI is voltage
driven and does not require a load. ILOAD comes on
when the amplifier is loaded, and its brightness is in
proportion to the output current. This is the ILOAD func­tion. In the event of current limiting action, the light will
flash to red. This is the ILIMIT function.

4.8 Mono Modes

The MA-5002VZ has three main operating modes,
namely dual (stereo), bridge mono, and parallel mono.

There are a number of precautions which should be
taken when operating the amplifier in either of the mono
modes. The VZ mode switches for each channel must
be set to the same setting. Sensitivity, LOI, and Com­pressor switches for channel 2 make no difference. The
input must be to channel 1 only. The input to channel 2
and controls for channel 2 are NOT defeated in either
mono mode, therefore no connection to channel 2 may
be made in either of the mono modes. The channel 2
level control should be turned down (counterclockwise)
fully in either mono mode.

Monaural amplifier operating modes are covered in
detail in the MA-5002VZ Reference Manual. The dis­cussion below primarily aids in understanding how the
mono modes work for testing purposes.

The Enable indicator is an amber light which indicates
presence of the low voltage supply . It is power ed by the
unregulated +24VDC supply. It will be on any time the
power switch is depressed (unless the low voltage fuse
blows).

ODEP indicators provide an on-line indication of ampli-

©2000 Crown International, Inc.

4.8.1 Bridge Mono

Bridge mono is intended for loads of 4 ohms or greater .
The feedback loop for channel 1 also drives the input
to channel 2 in this mono mode. The input to channel 2
is, however, inverted. This causes the output of chan­nel 2 to be of equal magnitude and opposite polarity
(for double voltage output). The output of the amplifier

Circuit Theory 4-13

MA-5002VZ Service Manual

130446-1 Rev. A

is balanced, and channel 1 hot output is connected to
load hot (+), channel 2 hot output is connected to load
return (– ).

4.8.2 Parallel Mono

Parallel mono is intended for loads less than 4 ohms
(as low as 1 ohm) in a monaural amplifier configuration.

The channel 1 and 2 amplifier hot outputs must be
shorted by an external shorting buss (10 AWG or larger).
The amplifier output to the load(s) is taken from either
channel’s hot output to load hot, and either channel’s
negative output to the load return (– ). The shorting buss
must be removed prior to changing from parallel mono
to either other mode.

4-14 Circuit Theory

Figure 4.9 Macro-Tech 5002VZ Amplifier Block Diagram

©2000 Crown International, Inc.

130446-1 Rev. A

5 Maintenance

5.1 Cautions and Warnings

DANGER: The outputs of this amplifier can produce
LETHAL energy levels! Be very careful when making
connections. Do not attempt to change output wiring
until the amplifier has been off at least 10 seconds.
WARNING: This unit is capable of pr oducing high sound
pressure levels. Continued exposure to high sound pres­sure levels can cause permanent hearing impairment
or loss. User caution is advised and ear protection is
recommended when using at high levels.

WARNING: Do not expose this unit to rain or moistur e.
WARNING: Only pr operly trained and qualified techni-

cians should attempt to service this unit. There are no
user serviceable parts inside.
WARNING: When performing service checks with the
power off, discharge the main power supply filter ca­pacitors fully before taking any measurements or touch­ing any electrical components. A 300-ohm 10-W resis­tor is recommended for this. Hold the resistor with pli­ers, as the resistor may become extremely hot.
WARNING: Under load, with a sine wave signal at full
power into both channels, the amplifier may draw in
excess of 30 amperes from the AC service mains.
WARNING: Do not change the position of the Mode
Switch when the amplifier is turned on. If the position of
this switch is changed while the amplifier is powered,
transients may damage your speakers.
WARNING: Heatsinks are not at ground potential. Si­multaneously touching either heatsink and ground, or
both heatsinks will cause electrical shock.
CA UTION: Eye protection should be worn at all times
when protective covers are removed and the amplifier
is plugged in.
CA UTION: Disconnect the power cord before install­ing or removing any cover or panel.

5.2 General Information

In most cases you will be using the test procedures in
Section 5.4 after conducting your repairs. Before ini­tially powering up the amplifier you should review Sec­tion 5.1 and take appropriate steps for personal and
equipment safety. Section 5.3 will help to determine
whether the amplifier should be safe to turn on.This
section also includes some additional checks that
should be made prior to starting the actual check-out.
Italicized print in the test procedures (Section 5.4) in­cludes basic troubleshooting hints to augment proce­dures in Section 5.3. These hints do not cover every
possibility, but should be helpful for a variety of symp-

MA-5002VZ Service Manual

toms. After troubleshooting and repair (or as a part of),
the final step is to thoroughly test the amplifier to be
certain that it meets the factory specifications. T est pro­cedures in Section 5.4 will help you do this as well as
aid you in locating the cause of problem(s).

5.3 Troubleshooting

5.3.1 Pre-AC-Checks

A number of checks can be made prior to powering up
the unit. These should be done in order to prevent an
unwanted disaster when turning the unit on. Once these
checks are made power may be applied for further
checks. Note: It will be necessary to remove top, rear,
and bottom panels for complete access to all modules.

Step 1: Acquire all information possible from the
person(s) having the problem to determine the nature
of the complaint. Ask questions like “Why was the am­plifier brought in for repair?” “Does it do this right at turn
on, does it take a while, or does it only happen some­times?” If you observe nothing wrong, inquire tactfully
how the unit was being used when the malfunction oc­curred to determine if it may have been misused, if the
user misunderstood what happened, or if another sys­tem component may be at fault.

Step 2: Always do a complete visual inspection. A prob­lem may be obvious just by looking. Things to look for
include burned components, wires not connected, fan
obstructions, loose hardware or connections, and sol­dering. Dirty air filters or plugged heatsinks greatly re­duce amplifier efficiency and result in pre-matur e ODEP
limiting. The fan blades should spin freely. Burns and
other physical damage should be repaired and com­ponents in the affected circuit areas should be checked
carefully before continuing.

Whether a problem is identified by visual inspection or
not, several checks should be performed prior to turn­ing the amplifier on. These should be performed if cata­strophic failure has been reported, no signal output with
constant IOC is reported, or the condition of the ampli­fier is otherwise unknown but failure is suspected.

Channel 1 uses 100/300 series numbering and chan­nel 2 uses 200/400 series numbering on the main mod­ule. 500 series numbering is used on the output and
emitter modules, regardless of the channel. 700 and
800 series numbers are used on control, current sense,
and terminator modules.

The third item on the “to do” list involves a number of
electrical checks. Due to the protection features of the
MA-5002VZ, it should be safe to turn-on under all cir­cumstances, but these preliminary checks may allow a

©2000 Crown International, Inc.

Maintenance 5-1

MA-5002VZ Service Manual

130446-1 Rev. A

partial, if not complete, repair before power is ever ap­plied. These checks are designed to find problems in
the output stages. The ultimate guide should always be
common sense.

To access all of the modules, simply remove the top
cover, rear panel, and bottom cover. The main module
will slide up and back for access to output module com­ponents by loosening four screws. The main module
tray need not be removed in order to remove an output
assembly , however , to perform component replacement
on the main module the tray should be removed com­pletely and the module removed from the tray. Note that
the current sense module is actually comprised of two
separate boards, connected by dual ribbon cables,
hardwired at both ends. The smaller board is called
current sense, the larger is, by itself, referred to as the
terminator. Either name, however, may be applied to
the pair. In Section 8 they are covered as a single part,
D 7994-3.

a.) Locate the flyback diodes D506, D507,
D508, and D509 on the emitter modules and check for
indications of a short. If a short is indicated, this means
that an output device or driver transistor in parallel with
that diode is shorted, usually not the diode itself. If a
faulty output device is found, the entire output assem­bly may be replaced, or only the affected components.
If an output device is found to be defective, emitter re­sistors should also be checked. If no output device is
found defective, perform a quick check of driver, pre­driver , and bias transistors. Then, if no problem is found,
move to power-on checks.

b.) Check driver and pre-driver transistors for
shorts or opens. If a fault is found, do an in-circuit static
check of all semiconductors on the output modules. If
no output device and nothing upstream is found defec­tive, move to power-on checks. Otherwise continue.

c.) If a failure has occurred anywhere in the
output stages, check bias servo transistors on each
(positive and negative) output module. Any failure as­sociated with bias transistors may result in repeat fail­ure of the affected channel even if all other defective
components have been found and replaced.

d.) If a failure is found in any LVAs, checks
should continue up onto the main module in the volt­age translator stage.

e.) Failure within the power supply itself is very
rare, however a cursory check of major items is always
prudent. A 30A fuse should not blow unless a cata­strophic failure has occurred in the output stage or
power supply. The low voltage fuse should not blow
unless a failure has occurred, probably in the supply
itself. If a failure has occurred in the output stages, check
the MOSFET switches and other VZ control components,
such as bridge rectifiers.

5.3.2 LED Checks

When power-of f checks are complete and any defects
found are corrected during that phase, the next step is
to apply power. The MA-5002VZ includes several LED
indicators to assist you in troubleshooting an amplifier
malfunction.

All indicators on the amplifier, both front panel and in­ternal, are important. External indicators include Enable,
ODEP, SPI/IOC, and I
clude DC/LF , Fault (output module), Standby, and Over­voltage/Transformer Ther mal.

A chart on the following pages lists likely LED combina­tions and likely causes. In each case it is assumed that
the LED circuit itself is operating properly. If a failure is
suspected, compare amplifier indicators with the chart.

In order to ensure that the problems ar e assessed cor­rectly , perform the LED checks under the following con­ditions: Before power is applied, ensure that the Ste­reo/Mono switch is in the STEREO position. Do NOT
connect any signal source or load to the amplifier. Turn
the amplifier on. After approximately 4 seconds the turn­on delay should time out. During the delay , IOC indica­tors will usually be on and ODEP indicators should be
off. After the delay times out, relays click on, IOC indi­cation should go off, and ODEP indicators should come
on. If this does not occur, definitely refer to the chart
that follows. Although this chart contains most likely fail­ures, it does not cover every possibility . Common sense
and a study of schematics and circuit theory (provided
in Section 4) should ultimately lead to a proper repair.

LOAD/ILIMIT. Internal indicators in-

5-2 Maintenance

©2000 Crown International, Inc.