Crown K-1 Service manual

K SERIESK SERIES

BALANCED CURRENT AMPLIFIER

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K SERIES

K SERIESK SERIES

Service Manual

BALANCED CURRENT AMPLIFIER

PROFESSIONAL AUDIO AMPLIFIERSPROFESSIONAL AUDIO AMPLIFIERS

PROFESSIONAL AUDIO AMPLIFIERS

PROFESSIONAL AUDIO AMPLIFIERSPROFESSIONAL AUDIO AMPLIFIERS

Models:

K1, K2

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Current Amplifier

K Series

amplifiers are produced by Crown International, Inc. Trademark Notice:

™ is a trademark, and

Crown®

and

BCA

are registered trademarks of Crown

Balanced

International, Inc. Other trademarks are the property of their respective owners.

KSVCK1K2

03/98

Rev. A

K Series 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 S.W., 1718 W. Mishawaka Rd., Elkhart IN 46517

Phone:

(800) 342-6939/(219) 294-8200

FAX:

(219) 294-8301

Web

: www.crownaudio.com

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.

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

Rev. A

K Series Service Manual

Revision History

Revision Number

None

Rev. A

Date

3-98 6-99

Changes

Initial Printing Added Revision History, Module and Schematic

Information, and Module Parts Sections. Upgraded Manual to Facilitate Component-Level Troubleshooting of PWA’s. Updated Cover Page and Table of Contents.

K Series Service Manual

Rev. A

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III

Rev. A

K Series Service Manual

Table of Contents

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

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

1.1.1 The K Series Amplifiers ........................................... 1-1

1.2 Warranty........................................................................... 1-1

1.3 Repair Strategy ................................................................ 1-2

1.4 Service Procedure ........................................................... 1-2

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

2.1 Performance .................................................................... 2-1

2.2 Controls............................................................................ 2-1

2.3 Indicators ......................................................................... 2-1

2.4 Input/Output..................................................................... 2-2

2.5 Output Signal ................................................................... 2-2

2.6 Protection......................................................................... 2-2

2.7 Construction..................................................................... 2-2

3 Theory...................................................................................... 3-1

3.0 Overview.......................................................................... 3-1

3.1 Power Supplies ................................................................ 3-1

3.1.1 Main Power Supply.................................................. 3-1

3.1.2 Low Voltage Supplies .............................................. 3-1

3.2 Input Stage ...................................................................... 3-2

3.3 DC Servo.......................................................................... 3-2

3.4 Sleep Circuit .................................................................... 3-2

3.5 Error Amp......................................................................... 3-2

3.6 Modulator......................................................................... 3-2

3.7 Triangle Generator ........................................................... 3-3

3.8 Proportional Vcc Generator ............................................. 3-3

3.9 Output.............................................................................. 3-3

3.10 Output Filter ................................................................... 3-3

3.11 Current Limiter ............................................................... 3-3

3.13 Overlap Correction and Adjustment .............................. 3-4

3.14 Display Circuitry............................................................. 3-4

3.15 Control Circuitry ............................................................. 3-4

3.16 Crowbar Circuitry........................................................... 3-5

4 Line Voltage Conversion ........................................................ 4-1

4.1 Line Voltage Conversion .................................................. 4-1

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

5.1 Where to Begin ................................................................ 5-1

5.2 Disassembly for Inspection & Service ............................. 5-1

K Series Service Manual

Rev. A

Table of Contents

5.2.1 Cover Removal ........................................................ 5-1

5.2.2 Power Supply Discharge ......................................... 5-2

5.2.3 Back Panel Assembly Removal............................... 5-2

5.2.4 Front Panel Assembly Removal............................... 5-3

5.2.5 Input PWA Removal................................................. 5-3

5.2.6 Main PWA Removal ................................................. 5-3

5.2.7 Output PWA Removal.............................................. 5-4

5.2.8 Control PWA Removal ............................................. 5-4

5.2.9 Line Filter PWA Removal ......................................... 5-4

5.2.10 Power Transformer Removal.................................. 5-4

5.2.11 Display PWA Removal........................................... 5-5

5.2.12 Bridge PWA Removal ............................................ 5-5

5.3 Troubleshooting ............................................................... 5-6

5.3.1 Identifying Symptoms.............................................. 5-6

5.3.2 Identifying and Repairing the Cause....................... 5-6

5.4 Required Test Equipment................................................. 5-8

5.5 Electrical Checkout Procedures....................................... 5-8

5.5.1 Quiescent AC Power Draw ...................................... 5-9

5.5.2 Gain Switches.......................................................... 5-9

5.5.3 “Y” Input Switch Operation...................................... 5-9

5.5.4 Bridge Mono Operation........................................... 5-9

5.5.5 Frequency Response ............................................ 5-10

5.5.6 Short Circuit Test ................................................... 5-10

5.5.7 Output Power......................................................... 5-10

5.5.8 Intermodulation Distortion ..................................... 5-10

5.5.9 Signal to Noise Ratio ............................................. 5-10

5.5.10 Crosstalk at 1 kHz................................................ 5-10

5.5.11 Post Test Settings ................................................ 5-11

5.6 Calibrations.................................................................... 5-11

5.6.1 Gaussian Filter Calibration .................................... 5-11

5.6.2 Overlap Correction and Adjustment...................... 5-11

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

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

7.1 General Information ......................................................... 7-1

7.2 Main Chassis Assembly................................................... 7-3

7.3 Front Panel Assembly ...................................................... 7-5

7.4 Back Panel Assembly ...................................................... 7-7

Rev. A

K Series Service Manual

Table of Contents

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

8.1 General Information ......................................................... 8-1

8.2 PWAs ............................................................................... 8-1

8.3 Schematics ...................................................................... 8-2

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

9.1 General Information ......................................................... 9-1

100438 PWA .......................................................................... 9-2

Component Map............................................................... 9-6

101554 Assembly .................................................................. 9-7

100469 PWA .......................................................................... 9-9

Component Map............................................................. 9-11

100497 PWA ........................................................................ 9-12

Component Map............................................................. 9-29

100524 PWA ........................................................................ 9-31

Component Map............................................................. 9-39

101014 PWA ........................................................................ 9-40

Component Map............................................................. 9-42

101809................................................................................. 9-43

Component Map............................................................. 9-51

101850 PWA ........................................................................ 9-52

Component Map............................................................. 9-54

101865 PWA ........................................................................ 9-55

Component Map............................................................. 9-57

102176 PWA ........................................................................ 9-58

Component Map............................................................. 9-62

102175 Assembly ................................................................ 9-63

102552 PWA ........................................................................ 9-65

Component Map............................................................. 9-67

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

K Series Service Manual

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K Series Service ManualRev A.

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BALANCED CURRENT AMPLIFIERBALANCED CURRENT AMPLIFIER

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Figure 1.1 The Crown K2 Amplifier

1 Introduction

1.1 Introduction

This manual contains complete service information on the Crown K1 and K2 power amplifiers. It contains service information for both non-CE and CE (European) units. It is designed 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!

1.1.1 The K Series Amplifiers

The K Series of power amplifiers are efficient, compact, high-power audio amplifiers designed for professional use. They provide full audio bandwidth, highpower amplification with minimum distortion. Crown’ s patented for maintenance-free operation with maximum perfor-

Balanced Current Amplifier™

design allows

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mance. Other features include convection cooling, balanced inputs, Bridge-Mono operation, “Y” Input for routing one signal to both channels, and input compression for maximum loudspeaker protection.

1.2 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 Technical Suppor t Group (within North America), or your Crown/Amcron Importer (outside North America). If you are an Authorized Warranty Ser vice Center and have questions regarding the warranty of a product, please contact the Field Service Manager or the T echnical Support Group.

Crown Customer Service

Technical Support Group

Factory Service

Parts Department

Mailing Address:

Shipping Address:

1718 W. Mishawaka Rd., Elkhart IN 46517

http://www.crownaudio.com

P.O. Box 1000, Elkhart IN 46515

Plant 2 S. W.

Phone: (219) 294-8200

Toll Free: (800) 342-6939

Fax: (219) 294-8301

Introduction 1-1

K Series Service Manual Rev A.

1.3 Repair Strategy

The

Balanced Current Amplifier

new era in Crown history. Taking full advantage of the modular design approach used in the design of

ries

amplifiers, we are able to offer a module exchange program for this product. The concept is that the PW A (Printed Wire Assembly) as a whole is one component, and when a part of the assembly is defective, the whole assembly is defective. Exceptions are the Control, Bridge, Display, and Line Filter PWAs. Those PWAs may be repair ed at the component level unless there is sufficient damage or malfunction to warrant PWA replacement. Non-PW A components are also excluded from this program.

Under the module exchange program, defective PWAs are returned to Crown for evaluation and rework. The reworked assemblies will then be stocked in the Crown Parts Department to be sold as refurbished parts.

This strategy offers several advantages. One advantage is less time spent in troubleshooting and repairing the amplifier, thus resulting in greater customer satisfaction. This strategy also allows Crown to collect the necessary information from amplifier failures, so improvements can be made for even greater product reliability.

technology rings in a

K Se-

1.4 Service Procedure

Servicing a tain steps to be followed. See Figure 1.2 for a flow chart of these steps. It is important that the defective Printed Wire Assemblies (PWAs) be r eturned to Crown for evaluation and repair . Under the module exchange program, warranty claims for PWA replacement will not be honored unless the defective PWA accompanies the warranty claim. In the event of a non-warranty repair, rebuilt PWAs will be available at a lower price than new PWAs, and a discount will be given if the defective PWA is returned to Crown.

Each PWA purchased from the Crown parts department will have a tag indicating that it is “Available for Issue.” This tag will have two parts. The first part simply states that the PWA is ready for use. It also has instructions for the PWA and the serial number of the module. Once the new PWA is installed, this part is to be discarded. The second part will be filled out by the service technician. After it is filled out with data such as the amplifier serial number and a description of the failure, it will be attached to the failed PWA. This part has three copies. The first is for the service center to keep. Copies 2 and 3 will remain together for use at Crown.

Balanced Current Amplifier

requires cer-

1-2 Introduction

WARNING

Component-level troubleshooting and repair of PWAs included in the module exchange program should not be attempted without expressed authorization from the Crown Audio Service Manager. Such an attempt, without specialized training and specialized test equipment, will likely result in substantial damage to the amplifier. Crown will not authorize payment of warranty claims in such an instance.

K Series Service ManualRev A.

Figure 1.2 Service Procedure Flow Chart

Introduction 1-3

K Series Service Manual Rev A.

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1-4 Introduction

2 Specifications

All specifications relate to both Export and Domestic

units, regardless of voltage and frequency.

2.1 Performance

Frequency Response

±0.25 dB from 20 Hz to 20 kHz. The frequency re-

sponse is band limited with an 8-Hz double-integrated

3rd-order Butterworth high-pass filter and a 30-kHz 7th-

order Gaussian low-pass filter .

K Series Service ManualRev A.

Power

An on/off rocker switch located on the front panel.

Input Sensitivity

A two–position switch for each channel, located on the back panel near each channel’ s input connectors. Can be set to 1.4 V for full output power into an 8-ohm load or a fixed voltage gain of 26 dB.

Bridge Output

An on/off switch located on the back panel between the input connectors. This switch, when turned on, bridges the two outputs with the channel one input signal.

Output Power

Measured at 1 kHz with both channels driven to 0.1%

or less true THD.

2 ohm Stereo: 750 watts per channel.

4 ohm Stereo: 550 watts per channel.

8 ohm Stereo: 350 watts per channel.

4 ohm Bridge Mono: 1,500 watts.

8 ohm Bridge Mono: 1,100 watts.

2 ohm Stereo: 1,250 watts per channel.

4 ohm Stereo: 800 watts per channel.

8 ohm Stereo: 500 watts per channel.

4 ohm Bridge Mono: 2,500 watts.

8 ohm Bridge Mono: 1,600 watts.

Signal-to-Noise Ratio

Greater than 100 dB below rated power , A-weighted.

Voltage Gain

1.4 VRMS input sensitivity or a fixed gain of 26 dB

(back panel switchable).

Damping Factor

Greater than 3,000 from 10 Hz to 400 Hz.

Line Voltage Requirements

Universal power supply can be configured to operate

with 100, 120, 200, 230, 240 or 250 V AC at 50 or 60 Hz.

2.2 Controls

Level

A calibrated rotary level control for each channel lo-

cated on the front panel. Each control is labeled from 0

to 100 dB of voltage attenuation.

“Y” Input

An on/off switch located on the back panel between the input connectors. This switch, when turned on, parallels the two input channels.

2.3 Indicators

Thermal

A red LED for each channel which turns on with a dim glow shortly before the amplifier needs help dissipating heat. The LED will turn brighter as the Thermal Level Control (TLC) protection is activated.

Clip

An orange LED for each channel which turns on when distortion of any type becomes audible in the amplifier output.

IOC

A yellow LED for each channel which serves as a distortion indicator . This indicator will light long before the distortion is audible. The IOC indicators include a pulse– stretching feature that helps make them more noticeable, even with rapid transient signals.

Signal

A green LED for each channel which flashes dimly when a very low–level signal (as low as 10 mW) is present in the output. They flash brightly when a louder signal (at least 1 watt) is present at the output.

Enable

A green LED that turns on when the amplifier has been turned on and has power. When first turned on, there will be a brief two–second delay while the amplifier performs a quick turn–on diagnostic. Then the Enable indicator will turn on to its full brightness. If no signal is present, the Enable indicator will switch to a dim level.

Specifications 2-1

K Series Service Manual Rev A.

2.4 Input/Output

Input Connectors

One balanced ¼–inch phone jack and one 3–pin female XLR connector for each channel.

Input Stage

Input is electronically balanced and employs precision 1% resistors.

Input Impedance

Nominally 20 K ohms, balanced. Nominally 10 K ohms, unbalanced.

Input Sensitivity

1.4 volts for standard 1 kHz power (33 dB of gain), or 26 dB gain.

Output Connectors

T wo sets of color–coded binding posts for banana plugs, spade lugs or bare wire. European models do not accept banana plugs.

DC Output Offset

±10 millivolts maximum.

2.5 Output Signal

Stereo

Unbalanced, two channel.

Bridge–Mono

Balanced, single–channel. Channel 1 controls are active; channel 2 should be turned down. For polarity the same as the input signal, use channel 1 output post as the speaker positive and the channel 2 output post as the speaker negative.

Out–of–band low–pass and high–pass filters protect the amplifier and loads from infrasonic frequencies below 8 Hz and ultrasonic frequencies above 30 kHz.

Tu rn On

State–of–the–art “soft start” feature prevents the amplifier from drawing a large inrush current when it is first turned on. This feature also assures that no dangerous artifacts are produced by the amplifier.

2.7 Construction

Chassis

Beautiful cast–aluminum front panel coated with a durable powder coat finish. Front panel labels are printed in color on Lexan for durability and fingerprinting resistance. Aluminum chassis with durable black finish.

Cooling

High performance passive convection cooling system allows the amplifier to drive 2-ohm loads to high music sound levels (8 dB into clip) in a 40° C environment without overthermalling.

Dimensions

Standard 19–inch (48.3-cm) rack mount width (EIA RS– 310–B), 3.5–inch (8.9-cm) height and 16–inch (40.6cm) depth behind front mounting surface.

Weight

32 pounds (14.6 kg).

38 pounds (17.3 kg).

2.6 Protection

General Protection

K-Series

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, DC offset and turn–on/turn–off transients.

TLC protection circuitry protects the amplifier from excessive heat by subtly and dynamically reducing the gain only when necessary to reduce heat levels. T ransformer overheating (an extremely unlikely event) will result in a temporary shutdown; when it has cooled to a safe temperature, the transformer will automatically reset itself.

2-2 Specifications

amplifiers are protected against shorted, open

Center of gravity approximately 6 inches (15.2-cm) behind front mounting surface and left-right centered.

3 Theory

3.0 Overview

This section of the manual explains the general op-

eration of the K Series power amplifier. Topics cov-

ered include Power Supplies, Input Stage, DC Servo,

Sleep Circuit, Error Amp, and Modulator. For Simplic-

ity, the circuit theory will only refer to channel one. It

may be assumed that channel two is identical to chan-

nel one.

3.1 Power Supplies

There are numer ous power supplies and voltage regu-

lators found within the K Series amplifiers. The main

high energy power supply and the low energy power

supplies are located on the main module.

3.1.1 Main Power Supply

The AC line cord is terminated through the fuse to the

AC line filter circuit. C1 is a .22uF capacitor and is

located across the line and neutral leads. C2 and C3

are .0047uF capacitors. C2 is connected from line to

ground and C3 is connected from neutral to ground.

This filter prevents unwanted emissions from contami-

nating the AC power line. The AC power then is routed

to the control board where the power-on relay, soft

start circuit and the AC line voltage configuration cir-

cuits take place.

When S1 is closed and power is first applied the relay

K1 is open and current passes through PTC (R1) to

the power transformer primary. The PTC restricts the

amount of inrush current while the transformer is en-

ergizing. When the power supply voltage reaches op-

erating voltage level the relay (K1) closes and by-

passes the PTC resistor. D1 is a diode bridge that is

configured to filter out any DC component on the AC

line. This is included to eliminate the possibility of

“T ransformer Buzz” which can occur when a torroidial

transformer is subjected to “dirty” or “noisy” AC power .

The primary wiring configuration for the multi-tap

torroidial power transformer (T1) is accomplished with

a connector plug that contains 9 connections. The

jumpers on the plug determine the amplifiers line volt-

age operating level. Line voltage reconfiguration can

be achieved by inserting the appropriately wired pug

(See Section 4) or by rewiring the existing plug.

K Series Service ManualRev A.

Full wave rectification is achieved by the bridge rectifying units D1 and D2 for the high energy supplies (±Vcc). C5 and C7 filter unwanted AC ripple from the ±Vcc power supplies.

D3, D4 and R1 detect low energy by sampling the transformer secondary voltage levels and passing this on to the Power OK circuit located on the Main module (to be covered later).

3.1.2 Low Voltage Power Supplies

On power up the ±Vcc power supplies first initiate. Once the +Vcc supplies are up to an operational level they power up the 125KHz oscillator: U9 and the gate driver: U10. The +Vcc is fed through F1 (3 amp fuse), L1 and R6. This sends+15V to both U9 and U10. The output of U10 is amplified by Q2, rectified by D3 and filtered by C15. The result is a regulated +15VDC. This +15V feeds U4 (+5V) which starts a 4MHz generator Y1/U6D (main schematic). The 4MHz output of U6D is sent to a divide-by chip, U5. U5 generates two outputs:

1. 500KHz–routed to the triangle generator (see Triangle generator circuit description).

2. 125KHz–routed back to the low voltage power supply. This 125KHz signal is fed back in order to drive a high frequency switch mode power supply . This SMPS consists of D4, D5, U11A, U11B, Q3 and Q4. U11A and B drive the 2 FET devices Q3 and Q4. The resulting output is a +7V 125KHz signal. The output of this switch mode power supply is routed in three directions:

1. Through C23 this supply is rectified and filtered by D10, D11, C24, and L5. The output is –13V.

2. Through C22 a 7VAC (15Vp-p) source is routed to the output stage. In the output stage T1 relays the power source to the full wave bridge (D01 and D02). Power Supply filtering is provided by C1, C2, C3 and C4. This +15V now feeds U03A and U03B (output stage FET drivers) and a +5V regulator (U01).

3. T1 Transformation: a. Using the primary coil of T1 the signal is filtered by

C26 and L6 to supply +7V. This +7V is used to feed a number of 5V regulators found on the main module.

b. T1 secondary #1: this power supply uses -Vcc as a

reference point. The output is labeled -Vcc+12. Since the K2 Vcc is ±103V the output of this power supply is –103V +12V = –98V. D12 and D13 provide rectification and C27 and C28 provide filtering.

Theory 3-1

K Series Service Manual Rev A.

c. T1 secondary#2: After rectification (D14 and D15)

and filtering (C29 and C30) B2+7 and B2-7 d. T1 secondary#3: After rectification (D16 and D17)

and filtering (C31 and C32) B1+7 and B1-7

4. Oscillator Sync: the final destination of the 125KHz signal is to synchronize the original 125KHz oscillator U9.

3.2 Input Stage

Both XLR and phone jack input connectors are in par allel with each other. While in most audio products the incoming shield is tied to the amplifiers ground network, (R100) paralleled with two .01uf capacitors(C100 and C135) for the purpose of inhibiting ground loop circulating currents and RFI protection.

The signal is fed to the balanced to unbalanced gain stage. Input impedance is 20K ohm balanced and 10K ohm unbalanced.

K Series

lections: 26dB and 1.4V. With the gain switch (S100) out the inverting gain stage is unity (gain of 1). With the gain switch (S100) in the inverting gain stage adds (depending on the amplifier model) the necessary gain to achieve 1.4V input sensitivity.

K Series

amplifiers come with two input sensitivity se-

amplifiers insert a 24 ohm resistor

mount. There are three filters that eliminate any AC component:

1. R147 and C121 for a 1 pole filter (-3 point is 8Hz).

2. The RC networks C114/R141 and C118/R148 each form a single pole filter.

The combination of all three filters form a three-pole filter leaving only the DC voltage.

3.4 Sleep Circuit

The sleep circuit monitors each channel for a signal. When no signal is present for approximately six seconds the sleep circuit sends a Standby signal to the main module turning off the carrier frequency within the modulator circuit. It takes approximately 0.5mV of input signal to bring the amplifier out of Sleep mode.

Signal is sampled from the second stage (U103A pin

1) of the Gaussian low pass filter. U5D generates the Standby control signal to place the amplifier in sleep mode. R17, R15 and C7 form the RC timing network that determines the time of switching states of U5D from +0.9V (awake) and –13V (asleep). The Standby control signal is routed to the base of Q102 through the diode D111.

Inherent within all PWM amplifiers is a rise in gain at higher frequencies. Because of this a 7th order Gaussian low pass filter has been included in the input stage of the filter is found immediately after the gain stage. U103A, U103B, U103C, U103D comprise this filter . U101D and R172 form the gain calibration stage for this 7th order Gaussian filter.

K Series

amplifiers. This Gaussian

3.3 DC Servo

Because the K series of amplifiers are DC coupled from the Gaussian Filter through to the amplifier output DC offset voltages can appear. This DC voltage can be amplified and the audio signal ride on top shifting its reference point r esulting in nonsymmetrical clipping. For this reason a DC correction circuit has been added. The non-inverting input of U105 is tied to the speaker output.

Since the purpose of U105 is to compensate for DC offset voltages elimination of any AC signal is para-

3.5 Error Amp

The audio signal enters the main module from the input module. the audio and negative feedback signals are both processed by the error amplifier U100D. From the error amplifier the signal is divided and is fed to the modulator . Since the modulator circuit is balanced the drive signal for the positive modulator is inverted by U100C.

3.6 Modulator

U101 and U103 are high speed differential comparators. The comparator section has two outputs: inverting and non-inverting. Therefore the output is balanced. The audio signal is applied to the inverting input of both differential comparators. The 250KHz triangle wave is applied to the non-inverting input of both differential comparators. With no audio signal the 250KHz is passed on to the NAND gate section of the differential comparator unchanged. Each NAND gate has two inputs: the modulated signal from the high speed comparater section and current limiter signal(U6A). In the event of over current the current limiter (U6A) signal is shut off disabling the NAND

3-2 Theory

K Series Service ManualRev A.

gates. This results in disrupting of the signal path.

The output of U101 is balanced and forms the posi-

tive portion of the output waveform (Vp). The output

of U103 is balanced and forms the negative portion

of the output waveform (Vn). These two balanced sig-

nal lines are routed to the output stage drivers, U02

and U52.

3.7 Triangle Generator

The 250KHz triangle wave has its origins from the

4MHz generator . After entering the divide-by chip (U5),

a 500KHz output signal (pin 9) is routed to U12B. The

output of U12B is a 250KHz square wave.

The 250KHz signal is then sent through U2C. U2C is

a linear IC with R186, R187, C153 and C154 in its

feedback loop. This stage converts the 250KHz

square wave into a triangle wave. From Pin 8 of U2C

and through C152 the 250Kz triangle wave is sent to

U105 which has two functions: gain and high fre-

quency filtering. C150, C151 and R162 serve to filter

the triangle wave signal.

The output of U105 is the 250KHz signal that is routed

to the positive and negative modulators, U101 and

U103.

cuitry . The output of U02 and U52 are then sent to the output MOSTFET drivers.

U03A, U03B, U53A and U53B are dual inverting high speed drivers designed to interface low current digital circuitry (U02 and U52) with power MOSFETs. U03A, U03B, U53A and U53B are used to drive the gates of the output FETs (Q1-Q4, Q51-Q54).

The output stage is divided into two sections, positive and negative. The signal is then routed to the BCA filter inductors (Ln and Lp) and the current sense resistors (R13/R14 and R63/R64). The combining point is then sent to the Output Filter.

With no audio modulation both negative and positive FET stages conduct. The frequency, phase and amplitude of output FET conduction is identical. Since the FET conduction signals are the same but opposite in polarity complete cancellation takes where the BCA filter inductors and current sense resistors connect. As the fundamental center frequency (250KHz) is modulated with audio differences in frequency, phase and amplitude appear and audio output develops from the BCA filter. This signal is then routed back to the Output Filters located on the main module.

3.8 Proportional Vcc Generator

The Proportional Vcc generator outputs a DC voltage

that varies as the ±Vcc levels vary. This varying DC

voltage influences the 250KHz output level. Because

output signal gain in a PWM amplifier can deviate as

VCC varies a DC voltage proportional to the Vcc sup-

plies is applied to the Triangle generator circuit.

U3C functions as the Proportional Vcc generator.

Through a resistor dropping network (R23/R24) +Vcc

is applied to the non-inverting input. Through another

resistor dropping network (R22/R21) –Vcc is applied

to the inverting input. On the output of U3A is a DC

voltage of 6.2VDC.Through diode D21 and resistor

R20 5.1VDC is applied to U12B.

3.9 Output

The modulated 250KHz signal exits the main module

and enters output assembly by means of U02 (Vp)

and U52 (Vn). U02 and U52 are optically coupled

gates giving electrical isolation from main module cir -

3.10 Output Filter

The output filter is made up of three individual filters: a 250KHz filter (L101/C127), a 500KHz filter (L102/ C131) and a final 250KHz filter. The signal passes through these three filters to eliminate both any residual 500KHz and 250KHz signals. The audio signal is the connected to the output speaker connectors.

3.11 Current Monitor

Audio output current levels are monitored by the use of transformer T100. A small primary winding is in series with the output line and the secondary develops a voltage related to the output current of the amplifier. This output current information is used for two purposes:

1. Negative feed back.

2. Current feedback information for the Triangle wave generator.

3.12 Current Limiter

To prevent excessive output current the K series am-

Theory 3-3

K Series Service Manual Rev A.

plifiers are incorporated with a current limiting protection circuit. The output current is sense by the cur rent sense resistors found in series with the BCA filter inductors. The voltage dropped across these two resistors is sent back to U106A and U106B. The voltage windows for U106A and U106B are set by the dropping resistors R303/R310 and the zener diodes D113/D114. The window voltage is ±0.7V. The outputs of the window comparator are normally +0.6V. This positive voltage is sent to U107A, an optically coupled gate. Pin 2 of U107A is tied to B1-7 and as long as pin 1 is positive the device conducts. The output is an inverting stage so when its input is positive its output will be negative. If the current limit detector switches states (becomes negative) pin 1 is negative and pin 7 becomes positive.

The output of U107A is routed to U6A (exclusive NOR) and as long its inputs are negative the output of U6A will be positive allowing the modulating network (U101 and U103) to output signal. If the output of U107A goes positive the output of U6A goes negative thus disabling the modulating circuit.

3.13 Overlap Correction and Adjustment

The Overlap adjustment corrects for DC shift in the T riangle waveform. In order to track thermal variations the Overlap adjustment potentiometer (R25) is located on each of the Output assemblies. A positive DC voltage is routed from the wiper arm of R26 to the Triangle wave gain stage. This DC voltage varies the DC component of the 250KHz waveform.

3.14 Display Circuitry

The

IOC

(Input Output Comparator) circuit uses the error signal from the error amplifier (U100D). With a window of ±0.3V U102A and U102D have a positive output. This in turn biases off D105 leaving a positive voltage on the base of Q103. If an error signal appears the ±0.3V window is overcome and the combined outputs become negative. This results in the output of U102C to go negative and in turn biasing on Q103. As Q103 biases on, E102 illuminates.

nal. When initialized U1B output (pin 7) becomes positive. After routed through the non-inverting input of U1A this positive signal turns on E100.

The signal used to switch on the Power LED comes from the Power OK control circuit. As this lime goes positive Q1 conducts lighting E1.

3.15 Control Circuitry

After initial power supply power up the outputs of U7C and U7D become positive (+1.2V). The output of U7 C and U7D is routed to two places: 1.) the first is the Power OK LED and 2.) then the Modulator able/disable comparator, U108A.. This positive logic signal causes the output of U108A to become positive (+1.3V) which next biases on Q102. With Q102 biased on the collector/emitter voltage is low (0.6V). Since U6A is a NOR gate and both inputs are low the output is a logic high allowing the modulator circuits (U101 and U103) to pass signal.

There are four functions that can disable the modulator circuit and disable the amplifier. These four inputs all effect the control line connected to pin 5 of U108A. The normal logic levels for this control line are: ON/

0.6 and OFF/–14). The four control functions are:

1. Initial Turn On Delay (U8A). On initial turn on the control line to U108A is logic low causing the modulator to be disabled. Once the capacitor found within the RC timing network (C161/R302) charges this comparator stage switches states allowing the Modulator to conduct. (Normal logic levels are ON/0.6 and OFF/

-14).

2. Over Temperature (U108B). In the event the amplifier overheats the output of U108B switches states disabling the Modulator.

3. Proportional Vcc (U8C). The Proportional Vcc circuit monitors the ±Vcc power supplies. In the event that the line voltage drops to far below the rated line voltage (causing erratic operation) U8C switches states disabling the Modulator circuit.

4. Current Limit (U108D).

A sample of the amplifier output (Fo CH1) is sent to U2A and U2B. This audio waveform sample then drives Q102 varying the current to the SPI (Signal Presence Indicator) LED E101.

The compressor circuit is initiated by either the initialization signal or The Thermal Limit Control sig-

IOC

3-4 Theory

If the amplifiers current limit is exceeded because of low impedances or a short circuit loading, U108D switches states and disables the modulator circuit.

K Series Service ManualRev A.

3.16 Crowbar Circuit

U13B and U13C form the DC protection comparator circuitry. R191, R192 and C156 form a combination resistive dividing and low pass filter networks. Signals below 8Hz (including DC voltages) cause the combined outputs to become a logic low (–14V). This logic level is inverted by the next comparator stage, U7B. a logic high (0.6V) causes Q10 to conduct. Once U7B switches states (logic high) U7A inverts this logic level and latches the Fault circuit in the Crowbar disabled condition. In order to clear this latched state the amplifier must be first turned off.

When the amplifier is turned on the line current conducts through the R1 (power supply circuit diagram) until the relay energizes. The relay primary is energized when Q8 is biased on. Q8 is biased on when Q7 is biased off (high collector/emitter voltage). When the relay closes R1 is bypassed allowing full power supply energy available to the output stage. If Q10 conducts Q7 is biased on and Q8 is biased off. This disables the power input relay.

Figure 3.1 Amplifier Block Diagram

Theory 3-5

K Series Service Manual Rev A.

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3-6 Theory

4 Line Voltage Conversion

K Series Service ManualRev A.

appropriate operating voltage. Figure 4.1 has information on jumper location for each voltage.

When wiring the molex connector the proper insertion and removal too should be used (example, Amp #458994-2).

4.1 Line Voltage Conversion

The

K Series

any line voltage in the world. It is also made to operate at 50- or 60-hertz frequency with no modification. To

amplifier can be configured to operate at

When converting from the 100V range to the 200V range, or vice versa, be sure and change the back panel line fuse. The fuse values and Crown Part Numbers are

listed in Figure 4.1. convert from one line voltage to another, change the V oltage Plug (P7), a 9 pin connector plug on the Control PWA. Refer to Figure 4.1 for the Crown Part Number of the plug you need. These plugs are available from the Crown Parts Department.

For your reference, Figure 4.2 shows the Control PWA,

P7, and the pin configuration of P7. T o access the Con-

trol PWA, remove the bottom cover of the amplifier.

The Control PWA is located in the center of the chas-

sis. For additional information on disassembly and asThe Voltage Plugs have jumpers installed which con-

sembly of the amplifier refer to Chapter 5. figure the primary power transformer windings for the

Voltage 100V 120V 130V 200V 220V 230V 240V 250V

Plug Part # 101230-1 101231-1 NA* NA* 101232-1 101233-1 101234-1 NA*

Voltage 5–7 5–8 1-8 2–4 2–4 2–4 1–4 1–4

Plug 6–2 6–1 3-4 5–7 5–8 5–9 5–8 5–9

Jumpers 3–4 3–4 5-9

Fuse K1: A10285-27, 15A K1: A10285-40, 8A

K2: A10285-28, 20A K2: A10285-26, 10A

* Voltage Plug not available. Voltage may be obtained by positioning the jumpers as indicated.

The Crown Part Number for the Voltage Jumper Wire is A11555-P025P. The Crown Part Number for the 9-Pin Molex Connector is C10303-3.

P12

Figure 4.1 Line V oltage Selection T able

P10

P11

5 6

Voltage Plug

Line Voltage Conversion 4-1

P13

Figure 4.2 Control PW A with Voltage Plug

K Series Service Manual Rev A.

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4-2 Line V oltage Conversion

5 Maintenance

K Series Service ManualRev A.

5.2 Disassembly for Inspection & Service

The extent of disassembly required will depend upon the extent of inspection and service required.

5.1 Where to Begin

Effective repair involves three basic steps: 1) Determine the symptom(s) of the problem; 2) Identify the cause(s) of the symptom(s); 3) Repair the unit to eliminate the cause(s). To deter mine the symptoms, you will want to get as much information from the user as possible. Get as much information as you can about the system and how the amplifier is used. There is always the possibility that the problem will show up only if used in a specific way.

Once you have all the information about the symptom(s), it is time to inspect the amplifier. A careful visual inspection is valuable for most problems which you may encounter . T o inspect the inside of the amplifier r emove the cover as described in Section 5.2.1.

Begin the inspection by looking for anything which appears abnormal, like loose connectors, broken wires and burnt or visibly damaged components. Inspect the printed circuit assemblies for broken traces and loose connections. Be thorough. The time you spend visually inspecting the amp is time well spent.

NOTE: TO A V OID THE RISK OF ELECTRIC SHOCK, TURN OFF AND UNPLUG THE AMPLIFIER FROM THE AC PO WER OUTLET BEFORE DISASSEMBLY

OR REASSEMBLY IS ATTEMPTED .

5.2.1 Bottom Cover Removal

To remove the cover of the amplifier you will need a #15 torx bit (TX15). After the cover is removed, and before any internal cables are disconnected, discharge the supplies. See Section 5.2.2.

1. Turn the amplifier on its side on your workbench. The only access to the inside of the amplifier is the bottom cover .

2. Using the TX15 bit, remove the 14 screws around the perimeter of the cover .

3. The cover lifts straight up after the screws are removed.

4. Vacuum out any metal particles in the unit that are a result of the lock washers digging into the chassis.

The cover on early units may appear to be symetrical but it’s not. When installing it onto the unit, make sure there is no gap between the front edge of the cover and the lip of the front panel extrusion. If installed backwards, there will be an

/8-inch overhang out the back of the unit.

/8-inch gap at the front, and an

WARNING

Amplifier components are ESD sensitive. When servicing the amplifier , the technician must have approved ESD protection. Proper grounding straps and test equipment are required. Failure to use proper protection will result in component failure.

WARNING

Before unplugging or plugging in any connectors or wires in the amplifier , discharge the power supplies. See section 5.2.2 for instructions. Failure to do so will result in circuit failure.

Maintenance 5-1

K Series Service Manual Rev A.

5.2.2 Power Supply Discharge

Before any connectors and PWAs are removed, the Power Supplies need to be discharged. Follow these simple steps.

1. Make sure the amplifier is unplugged from the AC power source.

2. Locate Test Point 1 (TP1) on the Main PWA. See Figure 5.1.

3. With a flat blade screwdriver or another metal object, short TP1 to the nearest resistor pad. This resistor is the second one from the end of a row of seven 3W resistors. Once the short is made you do not have to hold the screwdriver in place. The initial short triggers a latching triac circuit which discharges the supplies.

4. Wait a few seconds before attempting to disassemble the amplifier.

Caution: the three-watt resistors will become hot as the power supplies discharge.

5.2.3 Back Panel Assembly Removal

The back panel assembly is removed to access the Input and Main PWAs.

1. Follow the instructions in Section 5.2.2. Supply

discharge is necessary to avoid circuit damage.

2. Remove the aluminum shield by removing the two screws on the rear and the one on the control board.

Note: This shield is not used on early non-CE units.

3. Using a TX15 bit, remove the two screws on each side of the amp that hold the rear supports. See Figure 5.2.

Item A

4. Remove the five TX15 screws along the top rear of the amplifier.

Caution: These screws are shorter than the other cover screws and must be reinstalled in the same location or Main PW A will be shorted to chassis.

5. Remove the two TX15 screws on the Main PWA. See Figure 5.2.

Item B

6. Unplug the black and white wires (P8 & P9) and the ribbon cable (P4) from the Control PWA. See Figure

5.2.

Item C

7. Unplug the P1 ribbon cable from the Input PWA. See Figure 5.2.

Item D

8. Unplug the main wiring harness from the Main PWA. See Figure 5.2.

Item E

9. Remove the necessary tie wraps and unplug the ribbon cables from the Output PWAs. See Figure 5.2.

Item F

10. Gently slide the back panel assembly straight out the back of the amplifier. Note that the PC cards slide in the rails formed in the aluminium heatsink. Be careful of the wires and cables that will come with the assembly.

TP1 Resistor Pad

Figure 5.1 Discharge Test Point

5-2 Maintenance

K Series Service ManualRev A.

5.2.4 Front Panel Assembly Removal

The front panel assembly is removed to access the Power Switch, Display PWA, Bridge PWA and the Power Transformer.

1. Follow the instructions in Section 5.2.2. Supply

discharge is necessary to avoid circuit damage.

2. Using a TX 15 bit, remove two screws on each side of the amp located directly behind the rack ears. See Figure 5.2.

Item G

3. Remove the four TX 15 screws along the top front of the amplifier.

4. Unplug the main wiring harness from the Bridge PWA. See Figure 5.2.

Item H

5. Remove the P1 ribbon connector from the Input PWA. See Figure 5.2.

Item D

6. Remove the P5 and P6 transformer wire connectors, and P10, P11, P12 and P13 switch wires from the Control PWA. See Figure 5.2.

Item I

7. The Front Panel Assembly will now come off of the amplifier. Pull on the front panel handles while securing the chassis of the amplifier . Be careful of the wir es and cables that will come with the assembly. When reinstalling the Front Panel, make sure the capacitors on the Bridge PWA clear the aluminum heat sink and the Output PWA.

5.2.5 Input PWA Removal

The Back Panel Assembly must be removed to gain

access to the Input PWA.

1. Follow the instructions in Section 5.2.2. Supply

discharge is necessary to avoid circuit damage.

2. Remove the P2 ribbon cable from the Input PWA.

3. Using a #1 Phillips bit, remove the four screws that

hold the two female XLR jacks on the back panel.

4. Using a 5/8-inch nut driver, remove the two plastic

nuts that hold the 1/4-inch input jacks in place.

5. Using a TX15 bit, remove the two screws on the

back panel that hold the Input PWA in place.

6. Locate the plastic board stand–off between the Main

and Input PWAs. Using your fingernail or pliers, press

the release tab on the stand–off while gently lifting the

Input PWA off the stand–off.

7. While guiding the input jacks out of the holes in the

back panel, slowly lift the PWA out of the assembly.

5.2.6 Main PWA Removal

The Back Panel Assembly must be removed to gain

access to the Main PWA.

1. Follow the instructions in Section 5.2.2. Supply

discharge is necessary to avoid circuit damage.

Figure 5.2 Bottom View

Maintenance 5-3

K Series Service Manual Rev A.

2. Remove the P2 ribbon cable from the Input PWA.

3. Using a needle nose pliers, unplug the six red wires that go to the positive output binding posts. Note where they go.

4. Using a TX15 bit, remove the three screws that secure the Main PWA to the back panel.

Caution: Do not power up the amplifier without replacing these screws, or circuit damage to the Output PWAs will occur.

5. Locate the plastic board stand–off between the Main and Input PWAs. Using your fingernail or pliers, press the release tab on the stand–off while gently separating the two PWAs.

6. Lift the Main PWA away from the back panel. When installing the Main PWA onto the Back Panel Assembly be careful not to bend the capacitor located under the Line Filter PWA. If the unit is an early non-CE unit, the clearance between a capacitor on the Line Filter and a capacitor on the Main PWA is very small.

5.2.7 Output PWA Removal

The left and right Output PWAs are identical.

1. Follow the instructions in Section 5.2.2. Supply

discharge is necessary to avoid circuit damage.

2. Unplug the P01 ribbon connector and the P3 wiring harness connector from the Output PWA.

3. Using a TX15 bit, remove the screw located at the center–top of the assembly. See Figure 5.3.

Item A.

4. Using a TX20 bit, remove the six screws located by the four large coils on the assembly. See Figure 5.3.

Item B

Be very careful not to damage the coils with your screwdriver . Note that the screws have belleville washers on them. When replacing the screws be sure the cupped side of the washer is down toward the assembly.

5. Carefully lift the assembly out of the chassis. When reinstalling the Output Assembly use a new insulator pad and make sure there are no metal shavings on the pad or the heatsinks. Any metal shavings will result in a “blow–up” when the unit is first turned on. T o be sure that the insulator is free of shavings, and is installed correctly, use an Ohm Meter to check for continuity between the assembly heatsink and the chassis. There should be no continuity.

5.2.8 Control PWA Removal

1. Follow the instructions in Section 5.2.2. Supply discharge is necessary to avoid circuit damage.

2. Remove EMC shield on all but early non-CE units.

3. While noting where each wire goes, disconnect each connector on the Control PWA. The white wire goes on P9, and the black wire on P8. The two orange wires go on P10 and P11. The two purple wires go on P12 and P13.

4. To remove the Bridge Rectifier (D1) along with the PWA, use an

/32 -inch (.86 cm) nut driver to remove the nut. If you wish to leave the Bridge installed to the chassis then desolder the four rectifier pads.

5. Using a TX15 bit, remove the three screws that hold the Control PWA in place.

6. Lift the Control PWA out of the chassis.

Figure 5.3 Output PWA Screws

If replacing the PWA with a new one, be sure and remove the Voltage Plug (P7) and install it on the new PWA.

If replacing the Bridge Rectifier , be sur e and use ther mal heatsink compound between the rectifier and the chassis.

5.2.9 Line Filter PWA Removal (Early non-CE Units Only)

1. Follow the instructions in Section 5.2.2. Supply discharge is necessary to avoid circuit damage.

2. While noting where each wire goes, disconnect each wire from the PWA. The blue power cord wire goes on P4. The long black wire goes on P1, the white on P2. The short black wire from the fuse goes on P3.

3. Using a TX15 bit, remove the two screws that attach the assembly to the back panel.

4. Lift the Line Filter PWA out of the chassis.

5.2.10 Power Transformer Removal

The Front Panel Assembly must be removed in order to remove the Power T ransformer .

1. Follow the instructions in Section 5.2.2. Supply

discharge is necessary to avoid circuit damage.

5-4 Maintenance

K Series Service ManualRev A.

2. Clip the tie wrap which holds the orange and purple wires to the T ransformer Bracket.

3. Unplug the white wires from the Bridge PWA (P11, P12 and P13). Note that the white wire with the black ring attaches to P12.

4. Using a TX15 bit, remove the two screws which hold the T ransformer Bracket to the Front Panel.

5. Using a TX25 bit, remove the bolt which goes through the center of the transformer . The plastic bracket can now be removed.

6. While carefully lifting the transformer out of the front panel, route the white wires underneath the Bridge PWA. The transformer will now lift free of the front panel.

5.2.11 Display PWA Removal

The Front Panel Assembly must be removed in order to remove the Display PWA.

1. Follow the instructions in Section 5.2.2. Supply

discharge is necessary to avoid circuit damage.

2. The two level control knobs on the front panel are press fit onto the shafts. Remove these knobs.

3. Using a

-inch nut driver, remove the nuts on the

level control shafts. Also remove the flat washers.

4. Lift the Display PWA out of the Front Panel Assembly.

5.2.12 Bridge PWA Removal

The Front Panel Assembly must be removed in order to remove the Bridge PWA.

1. Follow the instructions in Section 5.2.2. Supply

discharge is necessary to avoid circuit damage.

2. Unplug the white transformer wires from the PWA. Note that the white wire with the black ring goes to P12.

3. Using a T20 bit, remove the two screws that hold the bridge rectifiers to the front panel. The screws have bellville washers. When installing the screws with the washers, make sure the cupped side of the washer is toward the bridge.

4. Using a T20 bit, remove the screw in the center of the PWA.

5. The bridge assembly will now lift out of the front panel. When installing it back into the front panel, make sure there is thermal heatsink compound between the bridges and the front panel.

Bridge PWA

Output PWA

Main PWA

Power Transformer

Display PWA

Control PWA

Output PWA

Input PWA

Figure 5.4 Discharge Test Point

Line Filter PWA

Figure 5.4 PWA Layout

Maintenance 5-5

K Series Service Manual Rev A.

5.3 Troubleshooting

As mentioned earlier, the three steps to effective repair are: Determine the symptoms; identify the cause of the symptoms; repair the unit to eliminate the cause.

The purpose of this section is to help you through these steps in an orderly manner.

5.3.1 Identifying Symptoms

Why was the amplifier brought in for repair? Can you get it to malfunction again? Some problems can be intermittent and difficult to find.

Once you have identified and verified the symptoms, you can look for helpful information in Section 5.3.2 as to where the cause of the problem is located.

If you don’t observe anything wrong with the amplifier , tactfully inquire how the owner used it and try to determine if it was misused or some other component in their system could have been at fault. Remember that the protection circuits in this amplifier will protect loudspeakers from problems caused upstream from the amplifier (DC protect).

If you lack sufficient information about the problem, and there aren’t any obvious problems with the amplifier , skip to Section 5.4, the Electrical Checkout Procedures.

5.3.2 Identifying and Repairing the Cause

The first step in identifying the cause of the problem is always a visual inspection. Once the bottom cover is removed, and the supplies are discharged, look for loose connectors, broken wires, loose hardware, burnt components, or bad solder joints on the PC boards. Any burnt components are a sure sign that the PWA will need to be replaced.

Once the visual inspection is complete you may proceed in powering up the unit. The best way to positively locate which PWA is at fault is to have a working PWA of each type on hand and plug them into the amplifier one at a time to see when the problem goes away . Output and Input PW As can be plugged into the amplifier easily without removing the old PWA. When doing so, use an insulating material to isolate it from the chassis and other PWAs. The Main PW A, however , needs to be installed into the chassis before it can be properly hooked up.

The following Symptoms and Causes may help you determine which corrective action to take. We realize that this list is limited. Please read through the Theory chapter in this manual to better understand the function of each PWA. This will help you come to your own conclusion as to the location of the problem.

Amp does not appear to power up. No Enable light.

First, check the power supply fuse. Also, make sure the AC line voltage is correct for the amplifier you are working on. Severely low AC line voltage could cause the amp to not power up. If both check out, then the amplifier is in a fault mode. The two most likely areas are the Main PWA or an Output PWA.

First, check the Output PWAs. Discharge the sup- plies, then disconnect the main wiring harness (P3) from the PWA in question. Now power up the unit. After the delay , if the enable light comes on, the disconnected Output PWA needs to be repaired or replaced.

To check if the Main PWA is at fault discharge the supplies, then unplug only one Output PWA from the main wiring harness (P3), and unplug the Input PWA (P2) from the Main PWA. Now apply power and check the +15VDC and the -13VDC. To do this, locate U7 on the Main PWA (next to where the Input PWA overlaps

5-6 Maintenance

WARNING

Before unplugging or plugging in any connectors or wires in the amplifier , discharge the power supplies. See section 5.2.2 for instructions. Failure to do so will result in circuit failure.

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Crown K-1 Service manual

Specifications and Main Features

Frequently Asked Questions

User Manual