Shure Pro Master 706, Pro Master 700 Service Manual

Price

0.00

700

AND

SERVICE

Manufactured by

SHURE

222

BROTHERS

Hartrey Avenue

706

SERIES

MANUAL

INC.

1981,

Shure Brothers Inc.

Evanston, Illinois

60204

U.S.A.

Printed in

U.S.A.

SPECIFICATIONS*

Type

................

.Solid-state power console using

discrete components and integrated circuits

Inputs

...............

.Six input channels (high andlor

balanced low impedance), plus

two aux input channels (7

and

lnput Channel Controls. VOLUME, INPUT ATTENUATOR,

A/B PAN

(700), LOW and HlGH FREQUENCY EQUALIZATION, EFFECTSIREVERB, MONITOR

Aux Channel Controls. Master Controls.

.VOLUME, A/B PAN (700)

......

.MASTER, EFFECTS SEND, RE-

VERB LOW and HlGH EQUAL-

IZATION, REVERB RETURN,

MONITOR MASTER

Outputs

.............

.SPEAKER, MONITOR, EQ OUT,

MIX OUT, EFFECTS, HEADPHONES, AUX, MIC

Common Mix Buses

...

.MIX OUTPUT, EQ OUTPUT (A, B

in 700)

Reverb and Effects

.....

Built-in reverberation unit; provi-

sions for connection to remote

reverb on-off switch and external effects devices

Graphic Equalizers.

...

.lo-band, fully combining, mini-

mum-phase, octave type, normally connected to power amplifier input; 13 dB boost or cut

at 63, 125, 250, 500 Hz,

1, 2, 4, 8 and 16 kHz; BELOW 63 Hz 12 dB/octave cutoff filter (10 dB down at 31 Hz)

LED Status Indicators.

INPUT CLIP, DB PEAKIfeedback

frequency, PA OVERLOAD,

POWER, TEMP WARNING,

SHUTDOWN

706;

700

Power Output

both channels one channel

with

driven driven

700

with

Per channel/4 ohms 200W min. 240W typical

channel/8 ohms 125W min. 145W typical

Per Measured at 1 kHz, 120

Vac, 1 % THD

Distortion

...........

.THD typically less than 0.1% at

40 Hz and kHz;

kHz, 0.25% at 15

IM distortion typically less than 0.25% [One channel driven, 180W or less to

ohms, 110W or less to 8 ohms, measured from low-impedance input with individual and master controls at typical settings (orange index marks)]

Low- and

High-

Frequency lnput

Equalization

........

13 dB at 100 Hz and 10 kHz

lnput Clipping

Indicators

.........

.Light

dB below input or equal-

izer clipping level

DB Peak Indicators.. Indicate power amplifier peak

...

voltage;

+6 dB LED indicates 100 watts sine-wave output to 4-ohm load. Rise time: 250

@ec to full-scale indication; fall time: 65 msec from full-scale to no indication

PA Overload

Indicators

.........

.Light when power amplifier THD

exceeds 1

;

fully on at

Temperature Warning

Indicator .Lights when output transistor

..........

temperature exceeds 70°C

(158°F)

....

Shutdown Indicator

Lights when power amplifier shut-

down occurs due to output transistor temperature over 100°C

(212"F), air flow or fan

failure, or dc at speaker output

lnput Sensitivity

(full power output).

...

BAL LO

HI AUX

PA INPUT

IMP

INPUT

IMP

0.6 mV

mV (700)

106

mV (706) 960 mV 960 mV

SPECIFICATIONS*

(continued)

BAL LO IMP 700 mV to 21 mV

Input Clipping Level.

Voltage Gain

.........

...

(INPUT ATTEN

-30 to 0)

HI IMP 10V to 335 mV (INPUT

AUX 30V to 10V (VOLUME

.94 dB BAL LO IMP INPUT to

ATTEN -30 to 0)

from

0 to 10)

SPEAKER OUTPUTS

71 dB HI IMP INPUT to SPEAKER

OUTPUTS

43 dB AUX INPUT to SPEAKER

OUTPUTS (700; 706: 49 dB)

64 dB BAL LO IMP INPUT to MIX

OUTPUT

77 dB BAL LO IMP INPUT to

MONITOR OUTPUT

74 dB BAL LO IMP INPUT to

EFFECTS OUTPUT

16 dB BAL LO IMP INPUT to MIC

OUTPUT

58 dB BAL LO IMP INPUT to AUX

OUTPUT

81 dB BAL LO IMP INPUT to

HEADPHONE OUTPUT

0 dB EQ INPUT to EQ OUTPUT

30 dB PA INPUT to SPEAKER

OUTPUTS

Levels and Impedances

Nominal Maximum Actual Working

Circuit Level Level Impedance Impedance

BAL LO IMP INPUT 5 mV 700 mV lk 19-300 ohms HI IMP INPUT 50 AUX INPUT MIX OUTPUT EFFECTS OUTPUT MONITOROUTPUT 1V 9V 2.4k 2k or more

INPUT 1V 1OV 50k 10k or less EQ OUTPUT AUX OUTPUT MIC OUTPUT 5 PA INPUT SPEAKER OUTPUT HEADPHONES

mV 10V 145k lOOk or less

0.5V 30V 50k 10k or less 1V 9V 2.4k 2k or more 1V 9V 2.4k 2k or more

1V 9V 2.4k 2k or more 1V 9V 5k 2k or more

mV 75 mV 70 ohms 19-300 ohms

1V 1OV 50k 10k or less

28.3V 1 OV 360 ohms 4 ohms or more

4 ohms or more

Frequency Response 22 dB, 40 to 20,000 Hz, BAL LO

...

IMP INPUT

to SPEAKER OUT-

PUTS

Hum and Noise

(20 Hz to 20 kHz).

....

dBV equivalent input (BAL

-127 LO IMP)

Noise

(300 Hz to 20 kHz).

...

dBV equivalent input (BAL

-128 LO IMP)

Signal-to-Noise Ratio .Greater than 80 dB (below full

output) at

typical control set-

tings (orange marks, MASTER

ATTEN at -12)

1.8k series

simplex onloff

Mic

lnput Simplex

Power

............

at 5, INPUT

.24 Vdc open-circuit,

resistance, switch

Power Requirements .Models 700 and 706: 120 Vac

lo%, 50160 Hz; 1100W (700), 600W (706) max. (Can be rewired for other

voltages; see

OPERATION AT OTHER VOLTAGES);

Models 700E6 and 706E6: 100, 120, 140, 200, 220 and 240

volts, 50160

(switch-

selectable).

Environmental

Conditions

Operating Storage

.........

...........

Overall Dimensions.

.-7" to 43°C (20" to 110°F) .-40" to 74°C (-40" to 165°F)

...

.l9O mm H x 584 mm W x 508 mm

D (7% in. x 23 in. x 20 in.)

Weight

..............

Construction

.........

.700: 21.3 kg (47 Ib)

706: 17.9 kg

(39% Ib)

.Molded construction with black

finish, carrying

handle, molded

rubber feet, line cord storage

Certifications

........

.Listed by Underwriters' Labora-

tories, Inc.; listed by Canadian Standards Association as Certified (700, 706)

*Measurement Conditions (unless otherwise specified): All volume and gain

controls for measured channel at maximum; unused channel controls at

equalization controls at 0. Measured input terminated as follows (unused inputs unterminated): BAL

4.7k. All outputs terminated as follows: all high-level outputs. 47k; MIC, 150 ohms; SPEAKER,

IMP, 150 ohms; HI IMP, 33k; AUX. EQ and PA.

ohms: HEADPHONES, 200 ohms.

TABLE OF CONTENTS

Section

SPECIFICATIONS DESCRIPTION MAINTENANCE

TROUBLESHOOTING CIRCUIT OPERATION

PA Overload LED Indicators DB PeakIFeedback FinderTM LEDS Feedback Finder Power Amplifier Protection Circuits

SERVICE INSTRUCTIONS

Replacement Parts FuseReplacement External Parts Service Access Reverb Pan Assembly Printed Circuit Boards DC Output Balance Adjustment DC Bias Current Adjustment DB Peak IndicatorsIFeedback Finder Frequency

Calibration

Full Wave Balance DB Peak LED Calibration Feedback Finder Calibration

Small Signal and Driver Transistors and

Integrated Circuits Driver Transistors Output Transistors Diode Bridge Rectifier Transistor and Diode Removal Active Component Checking Printed Circuit Board Connectors Ferrite Bead Rings

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vii

1 1

2 2

3 3 3

4 4 4

7 7

7 8

8 8

8 8 8 8

SERVICE ILLUSTRATIONS OPTIONAL ACCESSORIES GUARANTEE SHIPPING INSTRUCTIONS OPERATION AT OTHER VOLTAGES REPLACEMENT PARTS

NOTES TO SERVICE ILLUSTRATIONS

...................................

.......................

...............

LIST

.....................

............

9 9 9 9

11 17

Model 700

Model 706

DESCRIPTION

The Shure PRO MASTERTM Power Consoles are portable, high-power, eight-input mixer-amplifiers designed for use by professional entertainers and sound system operators. They are all solid-state units, employing the latest developments in integrated circuit, discrete component, and printed wiring technology. The PRO MASTER features pre-fader monitor, and exclusive FEEDBACK and PATCH BLOCKTM rear panel. Models 700 and 700E6

are stereo units, with twin Models 706 and

watt (rms) power amp.

Six input channels for microphones sources provide six high-impedance and six balanced

low-impedance inputs (which can be used simultaneously).

Each input channel is equipped with volume, 0-30 dB uator, high- and low-frequency equalization, effectdreverb and monitor controls. Two additional aux (only) input channels (7 and

Models 700 and

LED indicators show input clipping, power amp peak output level, power amp overload, power-on, temperature warning, and shutdown conditions.

Master controls include: master volume, effects send,

reverb high- and low-frequency equalization, reverb return

and monitor. Console outputs are: monitor, effects, stereo

headphones, aux, mic, and speakers. In addition, common mix buses are provided: mix output and equalizer output.

10-band graphic equalizer uses minimum-phase,

Each combining-type octave filters. Each filter is continuously

adjustable over a which is a 12

706E6 are mono units, with a single 200-

with volume controls are also provided.

700E6 also contain AIB PAN controls.

dB1octave cut-only switch. The FEEDBACK

200-watt

213 dB range, except for the lowest,

(rms) power amps, and

andlor aux level

FINDERTM

atten-

FINDER circuit switches the output level indicators to visual indicators of feedback frequency for eliminating feedback by graphic equalizer adjustment.

The built-in electromechanical spring-type reverberation device has provisions for connecting an external reverb onloff switch through the rear panel.

The rear-panel PATCH BLOCK contains a block diagram of the console's circuits, with patching jacks located in the diagram for easy reference.

The Model 700 and 706 consoles' regulated low-voltage power supplies operate over a 120 ation as low as 100 consoles can be rewired internally for operation at other voltages (see

unswitched ac receptacle for powering accessory equipment up to 100 watts is supplied. The Models

706E6 operate at switch-selected voltages of 100, 120, 140,

200, 220 and 240 volts.

simplex supply is provided for powering condenser micro-

phones. The consoles are protected against damage from open- or short-circuits on inputs or outputs, against heat damage by a cooling fan and automatic thermal shutdown circuit, and against radio frequency interference and line noise.

The structural foam molded cover is fastened to a

19 mm tile handle, rubber molded feet, and line cord storage.

Models 700 and 706 are Listed by Underwriters' Laboratories, Inc., and listed by Canadian Standards Association as Certified.

in.) wood bottom panel and contains a retrac-

Vac is possible at reduced output). The

OPERATION AT OTHER VOLTAGES).

LEDs from power amp peak

Vac * 10% range (oper-

700E6 and

Irf all models, a regulated 24 Vdc

MAINTENANCE

The PRO MASTERTM is an exceptionally well-designed unit. All components are of the highest quality, operating well within their respective ratings to assure long life. The following list of Do's and Don'ts describes minimal operat-

ing precautions and maintenance to provide years of dependable service.

DO clean the air filter every 100 hours of operation (more frequently in dusty or dirty areas). Stand the console on its rear bumpers, remove the screw securing the filter, and slide it out of its slot. Rinse the filter in water or a mild detergent solution, allow to dry, and replace.

DO unplug the console before cleaning. DO clean the outer surfaces of the console with a clean, damp cloth and mild detergent. DON'T use strong solvents or cleaning fluids.

DO use a l6AWG or larger (700, 700E6; 18 AWG for 706

706E6) heavy-duty extension cord when additional

line cord length is needed. DON'T operate the console with air louvers blocked, or

placed on a radiator or heat-producing equipment. Avoid operation in direct, hot sunlight.

DON'T replace the rear-panel fuse with a different size or type. Use only when operated at 100, 120 or 140 volts), or 5A, 250V, slow blow (for Model 700E6 when operated at 200, 220 or 240 volts. For Model 706, use a 4A, 250V SLOW BLOW fuse. For Model ated at 100, 120 or 140 volts, or a

BLOW fuse when operated at 200, 220 or 240 volts. DON'T connect the A and B speaker outputs together

(700 or setups.)

DON'T risk fire or shock hazard by operating the console in rain.

DON'T use UNbalanced low-impedance microphones

with the SIMPLEX 24V switch on; turn off the switch

if not required for powering condenser microphones. If simplex power is in use, connect unbalanced impedance microphones through a line matching trans-

former (Shure

700E6). (See Instruction Manual for monophonic

IOA, 250V (for Model 700, or 700E6

706E6, use a 5A, 250V fuse when oper-

3.15A, 250V SLOW

low-

A95FP) to a HI IMP INPUT.

TROUBLESHOOTING

Should any difficulty be encountered in console opera-

tion, the problem can often be traced to some simple

source such as an error in interconnection. The following is offered as a basic guide to this type of problem.

SYMPTOM OR CORRECTION

Console is "dead" (no output, POWER LED off)

1. Check that ac power source

2. Check that power

PROBABLE CAUSE

is "live" and that console is plugged in.

ONIOFF

switch is on. Check that rear-panel fuse

is good.

Console appears to be overheating (TEMP WARNING LED on)

Console power amplifiers turn off and remain off

LED

On)

No signal at speaker (all console functions

appear normal)

Console fuse blown

One of two inputs on same channel not working properly (both

%-inch and 3-pin jacks in use)

INPUT

CLIP LED

flashing

PA OVERLOAD LED flashes while DB PEAK

read

than

less

1. Check air louvers for blockage of proper air flow.

2. Check for proper speaker load

or shorted speaker cable.

3. Check air filter and clean if

necessary.

1. Check for proper air flow (fan

remains on during shutdown).

2. Check for hot air from left

louvers; console may have overheated (see above). Wait one minute to allow proper cooling.

3. Turn console off for a few seconds and turn back on.

4. If shutdown persists, have console checked by qualified service personnel.

1. Check for defective or erly connected speaker cables.

2. Check for improper tions to EQ or PA INPUT.

3. Check settings of channel VOLUME and MASTER volume controls.

1. Replace with identical fuse.

2. If second fuse blows, have console checked by qualified service personnel.

1. Make sure similar microphones are used on both inputs, and microphone impedances match the inputs used.

2. Make sure microphone is not used with accessory equipment on other input.

3. Make sure both microphone switches are on.

1. Adjust INPUT ATTEN to reduce channel input level.

Reduce input signal level at source.

1. Check for defective (shorted) speaker cable.

2. Check that load impedance is not too low (too many speakers connected).

improp-

connec-

No DB

cy band LEDindicators

flashing (console

output normal)

No console output; no DB PEAK LED indicatorsflashing

PEAK/frequen-

Make certain FEEDBACK

FINDER switch is set to A, B, ON or OFF (not between positions).

1. Check PATCH BLOCKTM rear panel for improper patching.

Check for improper connec-

tions to EQ or PA INPUT.

3. Check settings of channel VOLUME and MASTER volume controls.

Loud noise or clicks when certain microphones or cables are used

1. SIMPLEX 24V switch is on

(when not needed).

Unbalanced cable used when SIMPLEX 24V switch is on.

3. Check for defective micro-

phone cables.

No monitor output

(program output normal)

1. Check MONITOR OUTPUT connection to EQ or PA INPUT,

or external amplifier.

2. Make sure MONITOR and

MONITOR MASTER controls are turned up.

3. Monitor speaker volume control (if present) may be turned down.

Sound quality poor

(weak or thin)

1. Excessive equalization on graphic equalizers.

Defective input or patching cables.

Two simple methods of localizing problems without opening the console are as follows. These methods can be used to find the abnormal console section with or with-

out test equipment. (The methods are not needed

the problem is obvious: SHUTDOWN, no POWER indication, etc.)

With test equipment: Set all console controls to full

clockwise, REVERB RETURN control to full counterclock-

wise, and PAN (700) and EQ controls to center. Do not connect a speaker or headphone load. Apply a 0.5

mV, 1 kHz test signal across pins 2 and 3 of one of the BAL LO IMP input connectors. Normal voltmeter readings taken at each speaker, rear-panel PATCH panel HEADPHONES connector are given in Table

BLOCKTM and front-

The top row of figures indicates the voltage in each stage

from input to output. Similarly, a 5

mV signal inserted in a HI IMP input will check these same voltages. The other listed inputs give voltage indications only for those circuits

following the inserted signal. Ac voltages may vary

t30%

from the values shown.

Without test equipment: Using only a microphone and

speaker, it is often possible to isolate problem areas using

the PATCH BLOCK rear panel. The ability to bypass cer-

tain circuits and interchange channel signals provides a

simple but powerful tool for troubleshooting. For example,

a 700 console a suspected channel A equalizer

can

be checked by patching between the A MIX OUTPUT and A PA INPUT jacks. The signal bypasses the equalizer, and a talk test will immediately indicate whether the problem has been eliminated.

Similarly, a potentially defective channel B mix ampli-

fier can be verified by patching the A MIX OUTPUT to the

B MIX OUTPUT. The presence of a "clean" signal from

channel A to the B speaker output indicates that the prob-

lem precedes the B MIX OUTPUT jack. Further patching between the EFFECTS OUTPUT and B MIX OUTPUT jacks will isolate the problem to the B MIX amplifier.

INPUT

Bal

Imp 0.5 mV

Imp 5 mV

Aux

(700) 0.15V

AUX

(706) 64 mV

'Tip

ring

TABLE

0.54V

0.54V to

sleeve.

NOMINAL TEST VOLTAGES

OUTPUTS

Monitor

Effects

Mix

Aux

2.7V

0.54V

3.8V

2.7V

0.54V

Mic

7.0mV

0.54V

0.54V 0 54V

0.54V

Speaker

18.OV

18.0V 180V

Head-

phones*

11.5V

The above methods are extremely useful for saving time in localizing problem areas. In addition, they may allow use of the console in an emergency until repairs can be made. Internal servicing should only be performed by qualified

service personnel.

CIRCUIT

OPERATION

Most of the PRO MASTERTM circuitry uses conventional

operational amplifier technology, and can be serviced

using standard voltage-measurement procedures. However, certain circuits are unusual and may not be familiar

to many servicemen. This section describes these circuits as an aid to servicing (see Figures 5-38).

OVERLOAD LED INDICATORS

The PA OVERLOAD LEOS (01109) are designed to respond to error signals in their respective differential

amplifiers. The overload circuit is comprised of transistor

Q607 and associated resistors with the LED connected

across the collector and emitter of

Q607.

The power amplifier assembly input is the differential

amplifier

Q605-Q606, which amplifies the difference of the

signals at the bases (the input signal to Q605 and the nega-

tive feedback signal to

Q606). With small error signals (normal power amplifier operation), the dc voltage drop across turned on. low (approximately

R611 is approximately 1.6V, sufficient to keep Q607

Q607's collector-emitter voltage drop is very

O.IV), and as long as Q607 is on, the

associated overload LED is turned off.

When the differential amplifier input signals differ

greatly (such as when clipping or

place), the ac signal across about 1% distortion, the large ac signal through

V-l protection takes

R611 increases rapidly. At

R611 causes Q607 to turn off. With Q607 turned off, the current flow is through the associated LED and R616 to ground, lighting the LED.

Note that the circuit is sensitive to the actual power supply voltages; if the ac line input voltage is less than 120V, clipping and overload indication will take place at a lower output level. Note too that the LEDs remain on during shutdown; this is a normal condition because the power amplifiers are still partially powered during shutdown.

DB PEAK/FEEDBACK FINDERTM LEDS

With the FEEDBACK FINDER switch (S903) in the OFF

position, LED string

D1101-Dl108 indicates peak power amplifier output voltage values corresponding to indications of -36 to

indication is calibrated through

for a 20

Vrms sinusoidal output (100 watts to a 4-ohm load).

+6 dB at the SPEAKER OUTPUTS. A +6 dB

R919 (or R916, Model 700)

The power amp assembly (A6) has a resistive voltage

divider at the power amp output that feeds the DB CAL

potentiometer point at which the

then forwarded to a full-wave rectifier

R919. The DB CAL potentiometer sets the

$6 dB LED turns on. The ac signal is

(U920).

The rectifier is composed of two sections: a unity gain,

inverting precision half-wave rectifier formed by

U920A* and its associated components, and an inverting summing amplifier formed by

R1045 and R1040, and exhibits a voltage gain of

is via

U920B, which has two inputs. The first

approximately 1.5 times. The second input is from the output of the precision half-wave rectifier via

R1041. The gain

of this input is approximately 3 times.

When the input signal from the power amp is negative, the output of the precision half-wave rectifier is zero; when the input signal is positive, the rectifier output is negative. When the summing amplifier adds the rectifier output and the non-rectified signal together, the result is an output voltage that is always positive 1.5

VIN.

The FULL WAVE BAL adjustment (R1045) is used to trim the gain in one of the summing amplifier paths so that it is exactly one-half the gain of the half-wave rectifier path.

The output of the full-wave rectifier is fed to the network

comprised of

D940, C925 and R1037, which produces the

desired fast attack, slower decay operation. The dc voltage

developed at C925 is fed to the LED comparator string via

the FEEDBACK FINDER switch

(S903).

The dc output voltages from U920 drive the comparators U1101-U1102, which are referenced to a resistive voltage

divider. Each doubling of voltage on the input to the com-

parators turns on the next higher comparator, causing it

to light its associated LED, as well as keeping the LEDs below it

For example,

input voltage of 1.OV to the

lit.

comparator lights the -18 dB LED, as well as the -24,

-30 and -36 LEDS.

Model 700: Note that when S903 is turned to A or B for feedback determination, the corresponding LED string becomes a readout of frequency for that channel, and the other channel retains its dB peak indicating function.

FEEDBACK FINDERTM

The Equalizer outputs are fed to the FEEDBACK FINDER

switch

(S903) on the Output Controls board (A9), which

selects the desired output channel (A or B in Model 700)

for display. The FEEDBACK

FINDER circuit senses the frequency of the Equalizer signal and converts it to a dc voltage for display on the selected channel LEDs.

'Channel 8 only: channel A components are shown In the Model

Diagram.

700 A9

Circuit

Amplifier

square wave of approximately 1.2 Vpp.

tains the FEEDBACK FINDER THRESHOLD control

U916B clips the input signal to establish a

U916B also con-

(R999)

which is used to adjust the sensitivity of the circuit. U916B's output is capacitively coupled to comparator U903A via an RC filter

present in the signal. The first comparator

(R915, C909) that attenuates any ultrasonic noise

(U903A) is a zero-crossing detector, with the operating threshold set by the amount of hysteresis in the first stage.

The second comparator

(U903B) holds capacitor C910 discharged until the output of U903A goes high. The output of the third comparator

time as

reference voltage of (through

U903A, and stays high until C910 charges to the

7.5V. This time constant is adjustable

R972, FBF CAL) about the nominal 20 ,&ec period

(U903C) goes high at the same

to calibrate the frequency-to-voltage converter. The resul-

tant 20 switches a constant current source

Thus, the output of

pulse width of 20 input frequency. The current pulses are integrated

@ec pulse from U903D is inverted by U903C and

(Q901) on and off.

U903D is a pulse train with a constant

~sec and a repetition rate equal to the

capacitor C911 into a dc voltage which is directly proportional to the input frequency (approximately 12 Vdc output with an input frequency of 11 kHz). The dc output voltage is fed through switch S903 to the LED comparator strings to indicate the frequency band. For example, a 1 kHz signal will produce approximately 1 Vdc at

C911 and light the

LED above the 1 kHz graphic equalizer control (and all

lower frequency LEDs: 125, 250 and 500 Hz).

POWER AMPLIFIER PROTECTION CIRCUITS

Each power amplifier is protected by a voltage-current (V-I) sensing circuit which limits the V-l conditions in the output transistors to a safe level under overload conditions. Transistors Q610 and Q611 conduct under overload conditions and remove the input signal from the driver transistors (Q608 and Q609), thus limiting the dissipation of the output transistors

(Q612-Q615). A single-slope boundary is de-

fined by the values of the resistor network on the bases of

Q610 and Q611.

Thermistors RT602 and RT603 (mounted on transistor

Q614 and Q615 heat sinks) monitor the transistor case tem-

peratures.

RT602 and RT603 decrease in resistance as the case temperatures go up, causing the boundary to "pivot" to a lower value. The benefit of this arrangement is that under severe overload conditions, such as operating into a short circuit, dissipation is limited to a safe value. However, under normal conditions the protection boundary

moves out to allow operation with more severe "normal" loads than would otherwise be possible. Capacitors C609

and C610 insure stability during limiting.

Q603 provides pre-driver

When the current through

(Q601) protection as follows.

Q601 reaches a sufficiently high

level during overload, the increased voltage drop through

resistor

signal to

R614 is sensed by Q603, which then shorts out the

(2601, limiting its collector current to a safe value.

Diodes D609 and D608 are normally reverse-biased and do not conduct. But with highly reactive amplifier loads, the diodes will conduct to prevent reverse-voltage breakdown of the output transistors.

Thermistor

RT601 is mounted on output transistor Q613.

Comparators U503A and U503B compare a constant refer-

ence voltage of 0.73V to the voltage across RT601. When an unusually high temperature of on the heat sink, reference voltage and turning on ture continues to rise to drops below off Q502 and SHUTDOWN LED are partially powered but all other (low-level) circuits and the fan the temperature on the heat sink drops to

LEDs turn off and full power is restored to the power amps.

RT501 is a

with a threshold at

Power Supply board air flow through the PC board-fan assembly. When air motion is severely restricted, ance Increases (from 450 to approximately 1200 ohms). The current through R502 is reduced and the voltage drop across R502 is not enough to keep transistor turned on. (2501 turns off, opening relay K1 and turning on the SHUTDOWN LED. It is extremely important that

RT501 should be mounted in the path of the air flow, its

body perpendicular to the flow, approximately and not bent flat against the power supply board.,

The SPEAKER OUTPUTS dc sensor circuit is comprised of comparator U504 and associated components. A portion of the output voltage is derived from the divider network of R640 and comparator inputs, and capacitors C509 and the audio signal leaving only the dc component. When the dc output at the SPEAKER OUTPUTS jacks exceeds U504 changes state, cutting off transistors Q501 and (2502, opening relay K1, and turning on SHUTDOWN LED D802. Note that, when the comparator outputs change state, diode D509 and resistor

switch must be turned off and back on to reactivate the

console. This feature is designed to call attention to the

presence of excessive dc at the output, which is an abnormal condition and probably requires servicing.

theTEMP WARNING LED (D801). If the tempera-

(BI) remain fully on. This condition remains until

SERVICE

Voltages in this equipment are hazardous to life.

Refer servicing to qualified service personnel.

RT6Ol's voltage will have dropped to the

U503A or U503B will change state,

100°C (212OF), RT6Ol's voltage

0.3V, U503C or U503D changes state, turning Q501, opening relay K1, and turning on the

(D802). In this condition, the power amps

positive-temperature-coeffic~ent

120°C (248OF). It is mounted on the

(A5) in front of fan 61 in the path of the

R641 on the power amp board. It is fed to the

R518 cause "latching"; the power

INSTRUCTIONS

70°C (158OF) is reached

70°C, when the

thermistor

RT501 heats and its resist-

Q501

from

C510 remove

3QV,

REPLACEMENT PARTS

Parts that are readily available through local electronic parts distributors are not shown on the accompanying Parts List. Their values are shown on the Circuit Diagrams. Com-

mercial parts not readily available and unique parts are

shown on the Parts List and may be ordered directly from

the factory.

The commercial alternates shown on the Parts List are

not necessarily equivalents, but may be used in the event that direct factory replacements are not immediately available. To maintain the highest possible performance and

reliability Shure factory replacement parts should be used. When ordering replacement parts, specify the Shure Re-

placement Kit Number (RKC) or part number, description,

product model number, and serial number.

FUSE

REPLACEMENT

To replace line fuse F1, disconnect the line cord from

the ac source and remove the rear-panel fuseholder cap.

Replace the defective fuse as shown in the table. The following rear-panel symbols denote a fast-operating fuse

m~;

Model

700

700 700E6

700E6 706 706 706E6 706E6

'Rewired (see Operation at Other Voltages).

and a slow-blow (time lag) fuse

Operation

120Vac~10% 200,220,240 Vac* 100,120,140 Vac

200,220,240 Vac 120 Vac " 10% 200,220,240 100,120,140 Vac 200,220,240 Vac

Vac*

Fuse

IOA, 250V 5A, 250V IOA, 250V

5A, 250V,

Time Lag

250V,

4A, SLO BLO

3A, 250V,

SLO BLO

5A, 250V

3.1 5A,

250V,

Time Lag

Type

3AB, ABC 3AB, ABC 10A/250V

(6.3 x 32 mm) T5/250V

(5 x 20 mm) AGC, 3AG

AGC, 3AG

5A/250V (6.3 x 32 mm)

T3.15/250V

(5 x 20 mm)

,-CAUTION

If trouble symptoms-overheating, erratic operation, etc.-were apparent before the fuse blew, or if the

replacement fuse blows, a qualified serviceman should troubleshoot the console carefully to find the source of the trouble. fuses until the trouble is corrected.

Do not continue to replace

The Consoles also contain four fuses (F501-F504) on the Power Supply board necessary, replace only with identical fuses. Models 700 and 706 use type

leads. Models 700E6 and 706E6 use 5 mm x 20

250V, Time Lag fuses.

3AG, IA, 250V, SLO BLO, with "pigtail"

EXTERNAL PARTS

The following parts can be removed and replaced without disassembling the console:

Air Filter Knob, Rotary (MP2) Knob, Slider (MP3) Handle (MP4) Foot (MP5)

All knobs are pull-off types and are interchangeable.

SERVICE ACCESS

Disconnect the console from its ac power source. To open the console for servicing, carefully place the console on a firm, flat surface with the handle upward (sitting on the

rear bumpers). Remove the air filter and remove nine

screws and eight washers securing the bottom panel to the

cover (four from the front and five from the rear of the bottom panel). Carefully rotate the console until the bottom panel rests on the work surface and extend either side

(A5). If replacement becomes

(MP1)

mm,

lA,

/INPUT ALIGN. BRKT.

AIO

MP4

PRINTED CIRCUIT BOARD AND

PARTS LOCATION

FIGURE

about 5" over the edge of the work surface. Remove the two exposed screws from the bottom panel. Rotate the

console

180° and remove the remaining two exposed

screws. Lift the cover straight up. When clear of the bottom

panel, rotate it until the cover rests on its rear bumpers.

"open clamshell" position, with the bottom panel

This

horizontal and the cover vertical, provides access to all internal parts and assemblies (see Figure

1).

When closing the console, reassemble as follows to avoid damage. Remove the air filter (if not already removed). Bend and position the left wiring harness to fold

on top of the PC board-fan assembly. Bend and position the right wiring harness to fold between the fan and power transformer, clearing the fan blades. Center the cover over the bottom panel and lower the cover. With one side of the console extending about five inches over the edge of the work surface, replace four screws and washers in the exposed bottom panel holes. Rotate the console so that the other side extends over the edge of the work surface, and

replace four screws and washers. Raise the front of the

console so that it is sitting on the rear bumpers with the handle upward and replace the remaining screws and washers. NOTE: The screw next to the left handle mounting bracket does not use a washer. Replace the air filter.

REVERB PAN

To remove the reverb pan (AlO), disconnect the input and output leads from the reverb. Remove the screws and nuts holding the unit to the bottom cover plate. The cover plate and foam pads will remain in place. Secure the replacement pan to the cover plate, making sure the side

of the reverb with the phono jacks faces the front of the

console. Reattach the leads previously removed.

If the console is to be operated with the reverb pan re-

moved, make sure the associated leads are not free to short out any other wiring. Insulate and tie down the two reverb cables and ground lead.

PRINTED CIRCUIT BOARDS

The console's printed circuit boards are mounted by

various methods. The following paragraphs describe the

best method of removing each board after cable connec-

tors and connecting wires have been removed.

TANT:

When disconnecting cable connectors or soldered

IMPOR-

wire connections, make sure connectors or wires are identified for proper reconnection. This may be done by affix-

ing a piece of masking tape marked with the reference

designation (connectors) or terminal letter or color (wires).

Similar wire colors are used in different circuits; make sure proper re-connections can be made.

Push-on connectors must be removed by pulling straight out from printed circuit board surfaces. Do not apply side force when removing or reconnecting terminals, or damage may result.

Refer to Figure 1 for the location of each board. The

function of each board is given in the following table.

Board

No.

A1 A4 A5

A6 A7 A8 A9 All

Function

Input Controls (Ch. 1-6) Equalizer Regulated Power Supply Power Amplifier

(2)

Output Connectors

Input Connectors

Output Controls

LED Board

Component

Numbering

100s, 200s, 300s

400s 500s 600s 700s 800s

900s, 1000s

100s

A magnetic screwdriver is recommended for removing boards secured with screws. When removing front-panel

Y2"

jack retaining nuts with a

nutdriver or wrench, be care-

ful not to damage the surface around the jack. Boards or

parts secured with nylon standoffs may be removed by using a long-nose pliers to squeeze the locking lugs of the nylon standoffs on the circuit board side, and sliding the

board outward and off the standoffs. The printed circuit

board connectors can be reconnected for testing purposes after disassembly from the cover or bottom panel.

lnput Controls (Ch. and A8):

These boards must be removed at the same time.

1-6)

and lnput Connectors Boards (A1

Remove the knobs from the left (Input Controls) side of the front panel. Remove the nine retaining nuts and washers from the front-panel phone jacks (note that the

HEAD-

PHONES jack-J815-has an insulating washer behind

the metal washer.) Remove connectors

J1 and

J21

from

the lnput Connectors board and connector J2 from the

lnput Controls board. Remove connectors J24 and

J25

from the Output Controls board.

Use a long-nosed pliers to release the locking lugs on the board standoffs. As each standoff locking lug is released, push the potentiometer shaft in the vicinity of the standoff to disengage the board. Repeat this procedure for each

10 standoffs. As the lnput Controls board is disengaged

from the standoff, all the pot shafts except the six closest

to the lnput Connectors board will fall clear of the top

cover. Using the tips of the long-nosed pliers (or any blunt object that will clear the pot clearance holes in the cover),

push the six remaining pot shafts through the top cover.

After the lnput Controls board has been disengaged, free the three phone jacks on the right hand side from the top

cover by grasping the body of the HEADPHONES jack with

the thumb and forefinger, and pulling downward until the

bushing is free from the top cover. Repeat for the

AUX INPUT 7 and AUX INPUT 8 jacks. Free the left side of the lnput Connectors board by inserting a medium-size screw-

driver between the input alignment bracket and the cover. Start at Channel 6 and lift the screwdriver handle, freeing

&pin connector and phone jack from the top cover.

the

Repeat for all six channels. When all six channels have been freed, the lnput Connectors board and the lnput Controls board may be lifted out for service.

To reassemble, first make sure that the

LEDs are properly positioned. Position the lnput Connectors board in the top cover (do not assemble nuts or washers at this time). Position the lnput Controls board at the approximate location of the standoffs. The six rotary pot shafts closest to the front should be visible through their respective clearance

holes when viewed from the top of the cover. Reach through the respective clearance holes from the outside of the top cover using a hooked tool (or a formed paper

clipj and pop the rotary pot shafts into position. The remaining shafts will fall into position. Before snapping the

board into its locked position on the standoffs, check that the LEDs are aligned with their respective holes. Seat the board into its locked position. Assemble the washers and

nuts to the phone jacks on the Input Connectors board. Make sure that the insulating washer is behind the metal washer on the HEADPHONES jack. Check that the POWER,

TEMP WARNING, and SHUTDOWN LEDs are in their proper

locations. Replace all knobs.

Equalizer Board (A4):

of the foil side of the Output Controls board requires releasing the nylon standoff locking lugs holding

the board in place and pulling the board straight out. Dis-

connect the wiring harness connectors from J401 and

Regulated Power Supply Board (AS):

by disconnecting connectors J7, J8, and six screws along the edges of the board.

Power Amplifier Boards (A6):

boards (Model 700) are identical except for mounting brackets. Remove either board by first loosening the PC board-fan assembly. This is accomplished by removing four screws securing the boards to the bottom panel.

Select the power amplifier to be removed (channel B amplifier is toward the front of the console and channel A is toward the back).

Remove the electromagnetic shield (steel) and electrostatic shield (foil) by disconnecting the grounding lug and disengaging the shields from the nylon standoffs. Disconnect connectors J13 and J14 (for channel B; for channel A). Remove three screws from the edge of the Power Supply board and, using a small Phillips screwdriver, two screws from the fan.

Output Connectors Board (A7):

BLOCKTM jack retaining nuts and washers, remove board connectors J5 and J6 and unsolder three leads (yellow, green and black) to the MIC OUTPUT jack lifts straight out of the rear of the cover.

Output Controls Board (A9):

right side of the front panel. Remove the four screws with lockwashers and insulating washers, and disengage the five nylon standoffs securing the board to the front panel. Remove connectors J3, J4, J22, J23, J24 and J25.

LED Board (All):

can be removed after the Output Controls board removed. The LED board is located directly below the equalizer sliders, and can be removed by lifting upward.

DC OUTPUT BALANCE ADJUSTMENT

In order to eliminate dc offset at the output, a dc balance

control

Amplifier hand side of the console. The dc balance should be checked and adjusted as necessary whenever any Power Amplifier circuit components are replaced. The dc output balance adjustment should be made before making the dc bias current adjustment.

trols down and no speaker load. Connect a dc voltmeter

(preferably with a 0.1 Vdc full-scale range) across a

SPEAKER OUTPUTS jack (J16-J17 for channel A, for channel B).

(R601, blue) has been provided for each Power

(A6). This control is accessible from the left-

The dc balance adjustment is made with all volume con-

This board is located at the center

(A9). Removal

J402.

Remove this board

J9, and removing

The two Power Amplifier

J10 and J11

Remove all PATCH

(PI). The board

Remove the knobs from the

This board (two boards in the Model 700)

(A9) is

J18-J19

Use a small screwdriver with an insulated shaft to make this adjustment; hazardous voltages are present in the circuitry near

Carefully adjust the dc balance control for 0 Vdc -C20 mV at the output. NOTE: The normal adjustment range of R601 is

1V. If the dc offset exceeds this value, other problems

exist in the circuit.

DC BIAS CURRENT ADJUSTMENT

Each Power Amplifier (A6) contains a dc bias current adjustment control current through output transistors

ment minimizes crossover distortion without drawing excessive idling power. The bias current should be checked

whenever any Power Amplifier circuit components are re-

placed. The adjustment should be made after the dc output balance adjustment. Both dc bias current controls are

accessible from the left-hand side of the console.

The dc bias current adjustment is made with all volume controls down and no speaker load. Remove the Power Amplifier board shield and connect a dc voltmeter with a floating ground across resistor R632 (0.3 ohms, 7W). See Figures 28-31.

Use a small screwdriver with an insulated shaft to make this adjustment; hazardous voltages are present in the circuitry near

Starting with the dc bias current control at full counter-

clockwise, adjust it for 6

voltage should be present across resistors

R639.

DB PEAK INDICATORSIFEEDBACK FINDERTM CALIBRATION

The following calibration procedures should be per-

formed when parts in the DB PEAK LED strings have been

replaced. The potentiometers involved on board A9 are the

(R916), B DB (R919), FULL WAVE CAL A (R1044),

A DB

FULL WAVE CAL B (R1045), and FBF (R972). The balance

and dB peak calibrations that follow are given for output channel B; the identical steps for channel A use potentiometers R916 and formed with the cover open and the Output Controls board in place (see Figure 1). Note that the first two procedures apply to the Model 706 and to channel B of the Model 700.

Full Wave Balance

1. Set the console controls to typical settings (orange index marks), the INPUT MASTER controls to

2. Feed a 1 kHz, 150 mV signal from a low-distortion sine-wave signal generator to a channel input HI IMP jack. With an audio voltmeter connected (without a speaker load) to a B SPEAKER OUTPUT jack, adjust the B MASTER or signal generator level control for a 10V output.

3. Connect an oscilloscope across test point TP B (right center of

(R617, orange) to set the dc idling

A9) and ground (see Figures 18 and 20).

R601.

Q612-Q615. This adjust-

R617.

2 mV across R632. The same

R633, R638 and

R1044. All procedures can be per-

ATTENuators to 0, and the

The scope display should appear as in Figure 2A or B if the Full Wave is out of balance, or as in Figure 2C if it is in balance.

4. If out of balance, adjust the FULL WAVE CAL B (R1045) until the display looks like Figure 2C (alternate peaks have equal heights).

5. Repeat the above steps for channel A with the scope on test point TP A.

DB Peak LED Calibration

1. With the console, signal generator and voltmeter set up as for the Full Wave Balance procedure, vary

the signal generator level so that the output across the B SPEAKER OUTPUT jack is 20V.

2. Adjust the B DB

PEAK LED just barely turns on (dim or flickering).

3. Check for proper operation by decreasing the output 19V (the +6 LED should turn off) and increasing

to it to 21V (the

4. Repeat the above procedure for channel A.

Feedback

1. With the console, signal generator and voltmeter set

2. Set the FEEDBACK FINDER switch to B or ON.

3. Adjust the FBF

4. Check for proper operation by decreasing the signal

SMALL SIGNAL AND PREDRIVER TRANSISTORS AND INTEGRATED CIRCUITS

All transistors and integrated circuits are mounted on printed circuit boards. When replacing these parts it is imperative that proper lead configuration be followed. A minimum of soldering heat (25W maximum iron) should be

used to avoid damage to the part or printed circuit board.

When replacing regulators U501 or Type 120 thermal joint compound to assure good heat transfer. Refer to the

TIONS

DRIVER TRANSISTORS

Driver transistors Q608 and Q609 are mounted on heat sink brackets located on the surface of the Power Amplifier boards. transistors, apply Wakefield Type 120 thermal joint com-

pound to the surface of the transistor to provide good heat

transfer from transistor to bracket. Be sure that these

transistors are not interchanged in the circuit; they are not

identical devices.

FinderTM Calibration

up as for the Full Wave Balance procedure, adjust the signal generator for an 11.3 kHz signal.

barely turns on (dim or flickering). generator frequency to

should turn off) and increasing it to 11.5

kHz LED should be on brightly).

for transistor and integrated circuit lead codes.

Unsolder the transistor leads. When replacing

(R919) until the channel B +6 DB

+6 LED should be on brightly).

(R972) so that the 16 kHz (+6) LED

tl.O

kHz (the 16 kHz LED

kHz

(the 16

BALANCE WAVEFORMS

FIGURE

NOTES TO SERVICE ILLUSTRA-

Q608 is an NPN transistor and Q609 is a

U502, apply Wakefield

PNP transistor. Refer to the

TRATIONS

OUTPUT TRANSISTORS

Output transistors Q612 through black, finned heat sinks. The replacement procedure is the same as that used for driver transistors Q608 and except make certain the two diodes mounted below the heat sinks on Q612 and Q613 are thermally coupled (with Wakefield Type 120 thermal joint compound) to the heat sinks above them. Also, make sure that the thermistor assemblies are replaced, and the output transistors are

replaced in the same orientation as when they were removed. Position the thermistor lead wires so that they are not in contact with the heat sink or thermistor clip.

NOTE: When replacing output transistors, make certain the replacement transistor matches the other output transistors in part number and beta code (A, B or C).

DIODE BRIDGE RECTIFIER

Silicon diode bridge rectifier tom panel adjacent to power transformer

ing this component, apply Wakefield Type 120 thermal joint compound between the heat sink base of the rectifier and the bottom panel to provide heat transfer to the bottom plate. Note that the base of the rectifier is provided with a

locating pin. A notch is provided in the bottom plate to position the rectifier such that the locating pin fits into the notch. The terminals are marked to indicate the ac con-

nections to the power transformer and the output connections to filter capacitors

TRANSISTOR AND DIODE REMOVAL

Most transistors and all diodes used in the console are

mechanically supported by their leads. When replacing

these devices, proper lead configurations must be followed.

Minimum soldering heat (preferably with a low-wattage25W maximum-soldering iron) should be used to avoid damage to the device. Be sure to place heat-shrinkable tubing or "spaghetti" on leads where the original device

contained such tubing. Transistor lead codes are included

in the ACTIVE COMPONENT CHECKING

Integrated circuits can be checked without removing them from their circuit board. Measure the input, output and power supply voltages as shown on the applicable circuit diagram.

Defective transistors and diodes can be located by use of a standard ohmmeter such as a of the ohmmeter must be verified before these checks are made.

With a known diode orientation, measure the diode resistance in the forward and reverse directions. The lowest meter reading will establish the probe at the cathode end (schematic symbol arrow points to cathode) as the "minus" probe while the other probe will be "plus." Some ohmmeters are not polarized in this manner with relation to "volts plus probe" and "volts minus probe." With the ohmmeter "plus" probe on the anode end of a diode, and the "minus" probe on the cathode end, the ohmmeter should read approximately 2000 ohms or less. With the meter probes reversed, a reading of about 10,000 ohms or more should be obtained. If either of these conditions is not met, the diode should be replaced.

for transistor lead codes.

NOTES TO SERVICE ILLUSTRATIONS

NOTES TO SERVICE ILLUS-

Q615 are located on the

Q609,

Dl is mounted on the bot-

TI.

When replac-

"+"

and

"-"

C5 and C6.

(Figure 4).

Simpson 260. Polarity

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