JBL Class D Training Workbook Service Manual

harman consumer group

SERVICE CENTER TRAINING GUIDE

Servicing Class D Amplifiers

And The Theory of Operation

Introduction to Class D Amplifiers

Page 2

Harman Consumer Group 250 Crossways Park Dr. Woodbury, New York 11797

Email [email protected] Web www.harmanservice.com

I. A Brief Description of Other Audio Amplifier Classes

Class A

• Class A amplifiers are biased. The signal operates in the linear region between cutoff and saturation.

• The output devices conduct continuously, the bias current flows in the output devices at all times.

• In Class A operation, both devices are always on. There is never a time when one output or another is turned off.

• Class A is the most inefficient of all power amplifier designs.

• Class A amplifiers are large, very heavy and run very hot. All of this is due to the amplifier constantly operating at full power.

• Class A designs are the most linear, with the least amount of distortion.

I. A Brief Description of Other Audio Amplifier Classes (cont’d.)

Page 3

Harman Consumer Group 250 Crossways Park Dr. Woodbury, New York 11797

Email [email protected] Web www.harmanservice.com

Class B

• Class B operation is the opposite of Class A. Both output devices are never allowed to be on at the same time.

• The output devices have no bias (.6 volts is needed to bias each device).

• Each output device is on for exactly one half of the time. Class B designs have high efficiency but poor linearity; this is due to extreme crossover distortion.

I. A Brief Description of Other Audio Amplifier Classes (cont’d.)

Page 4

Harman Consumer Group 250 Crossways Park Dr. Woodbury, New York 11797

Email [email protected] Web www.harmanservice.com

Class A/B

• Class A/B is a combination of Class A and Class B.

• Class A/B operation allows both devices to be on at the same time that the outputs have a bias voltage, so current flows to the output devices more than half of the time but less than the full time of the output wave form.

This is called bias, and bias eliminates extreme crossover distortion.

I. A Brief Description of Other Audio Amplifier Classes (cont’d.)

Page 5

Harman Consumer Group 250 Crossways Park Dr. Woodbury, New York 11797

Email [email protected] Web www.harmanservice.com

Class C Class C is used in single frequency RF applications.

(Radio)

Class F There are no existing products that use this class of

amplifier. (You could be the first!)

Page 6

Harman Consumer Group 250 Crossways Park Dr. Woodbury, New York 11797

Email [email protected] Web www.harmanservice.com

I. A Brief Description of Other Audio Amplifier Classes (cont’d.)

Class G In Class G operation two power supplies’ voltages are

used. A Class A/B amp is connected to a low voltage rail and a diode transistor matrix. When the signal is greater than the lower voltage rail can supply, a transistor switch connects the output stage to a higher voltage rail. This involves changing the power supply voltage from a lower level to a higher level automatically when a larger output swing is required for large signal peaks.

I. A Brief Description of Other Audio Amplifier Classes (cont’d.)

Page 7

Harman Consumer Group 250 Crossways Park Dr. Woodbury, New York 11797

Email [email protected] Web www.harmanservice.com

Class H The Class H design is like the Class G, except that the

power supply tracks the audio input signal. This is the same as in the Bash power amps that we use in our amplifiers.

II. What Is Class D Amplification?

Page 8

Harman Consumer Group 250 Crossways Park Dr. Woodbury, New York 11797

Email [email protected] Web www.harmanservice.com

It’s a switched mode amplifier using “Pulse Width Modulation,” or, PWM.

The output signal is proportional to the ratio of positive and negative of the square wave. Then it is filtered by a low pass filter to remove the high frequency content of the square wave. If the duty cycle is 50% no output from the LC filter will be produced.

If the positive portion of the square is greater than 50% then the output will be a positive voltage from the LC network. If you modulate the square wave the output will vary proportionally to the modulated signal.

Page 9

Harman Consumer Group 250 Crossways Park Dr. Woodbury, New York 11797

Email [email protected] Web www.harmanservice.com

II. What Is Class D Amplification? (cont’d.)

oscillator to the input

The output of the of the opamp U6:A is

a ramp waveform.

The input signal is modulated with a much higher fixed frequency. The waveform of the fixed frequency is a saw-tooth signal formed from the 100khz ramp generator.

Fig. A

Fig. B

Fig. C

Page 10

Harman Consumer Group 250 Crossways Park Dr. Woodbury, New York 11797

Email [email protected] Web www.harmanservice.com

II. What Is Class D Amplification? (cont’d.) Class D Modulation is obtained by using an opamp as a

summer to achieve PWM.

On our Class D Amps the oscillator, feedback and audio all feed into one input of the opamp.

The result is a summation of all the signals at pin 2 of IC U6 with a result of a square wave out at pin 1 of U6.

Note: The opamps gain is very high due to 2.2meg feedback resistor R50.

II. What Is Class D Amplification? (cont’d.)

Page 11

Harman Consumer Group 250 Crossways Park Dr. Woodbury, New York 11797

Email [email protected] Web www.harmanservice.com

Feedback

Purpose:

• To compensate for nonlinearities either in the amplifier stage or the load with the end purpose of reducing distortion.

• We use two feedback paths for our design; the main one is before the output inductor (L3 on most amps). It consists of a low pass filter to remove the carrier and reconstruct the modulated audio signal. This signal is fed to amplifier U6.

• The second feedback path we will call the AC sine sense, and it’s taken after the low pass filter. This is a minor feedback and is used for additional stability.

II. What Is Class D Amplification? (cont’d.)

Page 12

Harman Consumer Group 250 Crossways Park Dr. Woodbury, New York 11797

Email [email protected] Web www.harmanservice.com

+15VSW is

referenced from –V,

not ground

Always check the +/-15 Volt supply. It is the supply for all of the opamps.

VCC of U7 (IR2111) is delayed at turn on (mute release). U7 is the drive that insures that the mosfets never turn on at the same time.

II. What Is Class D Amplification? (cont’d.)

Page 13

Harman Consumer Group 250 Crossways Park Dr. Woodbury, New York 11797

Email [email protected] Web www.harmanservice.com

Protect

only

triggers mute

Base of Q10 goes low. Voltage at Q10 goes up, turning on Q7. This then puts the amp in mute.

Remember!

Protection is only MUTE (standby mode).

Page 14

Harman Consumer Group 250 Crossways Park Dr. Woodbury, New York 11797

Email [email protected] Web www.harmanservice.com

II. What Is Class D Amplification? (cont’d.) BTL Class D

Opamp

A

This is the output block of the JBL S120PII. All that was added to the amp was a second FET output stage and opamp A. Opamp A has no gain, and is used for phase

nd

inversion of the audio to the 2

FET output stage.

When servicing this amp, please remember that the speaker out +/- is hot to ground.

Never ground the S-.

II. What Is Class D Amplification? (cont’d.)

Page 15

Harman Consumer Group 250 Crossways Park Dr. Woodbury, New York 11797

Email [email protected] Web www.harmanservice.com

Class D Power Amp Harman/Kardon HKTS 10/20

The HKTS10/20 is different from other Class D amps because it uses discrete components for the FET drivers and the output FETs themselves.

The drivers and outputs are Class B amps. They are used to insure that the mosfets never turn on at the same time.

The mosfets are IRF640 and IRF9640. They are built with Schottky diodes inside the FETs. The amps contain inductors (low pass filters) and drive loads with will clamp fly-back voltages and clamp waveforms that have

inductance. The diodes

overshoot.

Page 16

Harman Consumer Group 250 Crossways Park Dr. Woodbury, New York 11797

Email [email protected] Web www.harmanservice.com

Service Bulletin JBL2003-06 - April 2003 This is considered a Minor repair

To: All JBL Service Centers

Model: S120PII

Subject: Distortion When Coming Out Of Standby

In the event you receive an S120PII subwoofer with the complaint “There is a brief chirping sound, or short oscillation that occurs when the unit is in the AUTO mode, in Standby, when it’s triggered ON with a music signal”, follow the procedure below to correct this condition:

Synopsis: Replace D60 (RLS4148 diode) with a 3.6V Zener Diode; add new Resistor.

1) Remove the amplifier assembly from the subwoofer cabinet (12 Phillips screws).

2) Remove the Plastic Amp Cover from the faceplate (4 Phillips screws).

3) The area of concern is on the Class D Driver PCB (Small Upright PCB on the MAIN AMP PCB). A long, thin, soldering iron tip is recommended. Care must be taken not to damage surrounding components, like large inductor pair L8.

4) Locate, remove D60 (RLS4148 diode); replace with a 3.6V zener diode, JBL Part# ZMM5227BCT-ND. When replacing D60 the polarity of the new (zener) diode should be reversed

5) Add new 27KΩ resistor, JBL Part# 299-27K, to the indicated connections. (This component, electrically, will be in parallel with R37, reducing its value to <22KΩ). Assure the leads do not come into contact with any other connections; insulate the leads if necessary.

6) Replace amp cover and return amplifer assembly to cabinet.

7) Test the subwoofer to assure the distortion is no longer present.

Service Bulletin

.

Page 17

Troubleshooting tips and solutions to common service problems

For models: PS-10, PS-12, SUB750 TIP# INFTT2003-04

Subject: Replacing MOSFETS Q18, Q22

In the event you need to replace MOSFET transistors Q18 or Q22 as part of a repair, it is important to use

ONLY the Infinity part# FE106401110 or only the brands: International Rectifier, or Fairchild.

Replace both Q18 and Q22 MOSFET’s in the circuit, even if only one seems to be damaged.

Do NOT mix & match these components from different manufacturers, or batches. They should be

identical.

TECH TIPS

Harman Consumer Group 250 Crossways Park Dr. Woodbury, New York 11797

Email [email protected] Web www.harmanservice.com

E250P

Page 18

Harman Consumer Group 250 Crossways Park Dr. Woodbury, New York 11797

Email [email protected] Web www.harmanservice.com

DETAILED TROUBLESHOOTING

A. Power Amp Section

Resistance

Check

Resistance from S+ (SPK O/P) to GND should be >1M Ω (NO LOAD)

Resistance from V+ (C6 P+) to V- (C8 P-) gradually Fully CHARGED should read >10k Ω Resistance from V+ (C6 P+) to S+ (SPK O/P) should read >1MΩ Resistance from V- (C8 P-) to S+ (SPK O/P) should read >1M Ω

2. Power Up LED RED

With a 5mV signal to Low level input, LED should change to GREEN

-Voltage measurements (DVM)

OP AMP

LED

P-U4(1) P-U4(7)

RED 0Vrms 11.84VDC

GREEN 7.13Vrms -12.93VDC

3. D.C. Operation

-Voltage measurements (DVM) on CLASS D POWER AMP

Between V+ Q4(E) Q1(C)

And This

Point

Get this

Reading

GND V- GND GND GND GND GND GND GND GND

71.7V 0V -71.7V 0V -71.7V -71.5V -71.2V 0V 0V 4.65V

Q10(C)

U7(1) U7(2) U7(4) U7(6) U7(7) U7(8)

4. Check Switching Frequency

• Oscilloscope - USE THE PROBE TIP TO U6(7) TO GND

• Reading 100kHz +/-10%,24Vp-p

B. Pre Amp Section

Line Level Input Sensitivity

-Set up Turn level, X’OVER FREQ POT Fully CW and LFE switch off

Generator Set at 200mV@50Hz

Signal to Line level input

E250P

Page 19

Harman Consumer Group 250 Crossways Park Dr. Woodbury, New York 11797

Email [email protected] Web www.harmanservice.com

DETAILED TROUBLESHOOTING (CONT'D)

- Voltage measurements

OP AMP

U2(1) U2(14) U2(8) U3(7) U3(1) U3(14) U3(8) U5(7) U5(1)

306.9mV 461mV 460mV 658mV 628mV 598mV 2.326V 2.02V 3.57V 23.33V

2. High Level Input Sensitivity

-Set up Turn level, X’OVER FREQ POT Fully CW and LFE switch off

Set Generator at 1.3V@50Hz

Signal to High level input

-Voltage measurements 15.3V at speaker output

3. Low-Pass

-Set up Set Generator at 200 mV@100Hz

Signal to

Measure voltage at S+ speaker output

-Voltage measurement

X’OVER FREQ. Setting Output

CW 14.03V

CCW 4.8V

Line level input

SPEAKER

O/P

4. LFE

-Set up Set Generator at 200mV@200Hz

Signal to

Measure voltage at S+ speaker output

LFE switch Setting Output

Normal 6V

LFE 18.32V

See flow chart next page for diagnostics.

Line level input

,

E250P

Page 20

Harman Consumer Group 250 Crossways Park Dr. Woodbury, New York 11797

Email [email protected] Web www.harmanservice.com

DETAILED TROUBLESHOOTING (CONT'D)

FLOW CHART

TO GROUND. ALL TEST INSTRUMENTS CONNECTED TO THE OUTPUT MUST

BE FLOATING. ATTACH THE SCOPE PROBE TIP TO S - and REFERENCE

LEAD TO S+.

(A 10mV signal may need from the input to trigger the Switch turn on)

START

Resistance check

(no load)

between V+ V-,

V+ O/P,V- O/P

and O/P to GND

is > 10K

no

OK

yes

Power up with no

signal input

LED RED

CAUTION : SPEAKER OUTPUT IS FLOATING AND IS NOT PROTECTED AGAINST A SHORT

Check +/-15V-MOD

+/-15V voltage at

U 6(8),U6(4)

Check

FB1,FB2,C45,

Replace

Q18,Q22

OK

I/P:10mv/50HZ

Check +15V/SW

Q4(E) TO V-

C50,C60,C63,

R81,R82

no

OK

yes

Check Q4(E)

TO V-

= 0V D.C.

no

OK

yes

Use scope to check

switching

frequency U6(7)

100KHz

+/-10% , ~24Vp-p

no

OK

yes

CLASS D AMP OK

Discharge C37,

Check fuse

transformer, L4,

rectifier, C6 and C8

Check

MUTE(+8V) and

Q24,Q25,Q26

OK

Check

U7(1) = -58.3V

OK

Use scope to

check O/P U7(6)

and GND

143Vp-p square

wave shown

OK

Check

L2,L3,C71,C72,

C73

C74

Check

MUTE(-12.9V),

And

Q24,Q25,Q26

Check

U7,Q16,Q17,

Q20,Q21,R87,

D26,D35,C64

E250P

Page 21

SCHEMATICS

Harman Consumer Group 250 Crossways Park Dr. Woodbury, New York 11797

Email [email protected] Web www.harmanservice.com

Page 22

E250P

Harman Consumer Group 250 Crossways Park Dr. Woodbury, New York 11797

Email [email protected] Web www.harmanservice.com

S120PII Studio Series

Page 23

Harman Consumer Group 250 Crossways Park Dr. Woodbury, New York 11797

Email [email protected] Web www.harmanservice.com

S120PII Studio Series

Page 24

Harman Consumer Group 250 Crossways Park Dr. Woodbury, New York 11797 Email [email protected] Web www.harmanservice.com