Sherwood SEL-400 User manual

XL4oo

SHER\ATOOf)

MODEL

SEL-4OO

\-,

I. SELECTOR:

Selaets

Iistening

source:

llic,

Phcro

2,

Phono |

1

Tuner, Aux

l, or Aux 2.

2.

!,98:

Providee for

eelqctron

of

Steteo,

Stereo

Reverse,

tlono,

Left, ot

Right

Channels.

3-

tQEE&i['

Tells

lou

that th! arplificr

is th.

4. FUilCTI0ft

LI6HT5:

Tells

you

the

poaition

of

tha Salector

control.

5.

.SSKEE:

Selactg

llain epaakers,

Rcrote,

Both,

or Off.

6.

L0UIINESS/V0LUHE:

l4aetcr Porer

ON/OFF

and Volurc

Control.

AIeo autonstically

adda

bass colpense-

tion at

loy lsvcle

rhan thc

Loudnaes

eritch

ie depreaaed.

7.

!I9.:

Input

jacke

for

Left and Right

channel

nicrophoncs.

8.

S,g,:

Increases

Bass

tones up to +16d8,

decreases

to

-l6dB.

e.

EM!,9E'

Incrcaaes llidrange

tonca up to +6d8,

decreaaee

to

-6d8.

r0.

f!!!!!:

Increaees

Treble tonca

up to +16d8,

decreages

to

-l6dB.

STEREO AMPLIFIER

SERVICE MANUAT

1r.

@EQ_8!.9!,E9.:

Two

jacks

for

ptivate

listening with

ona or two

seta of

stereo headohonee.

1

2.

BALANEE:

EEf$E?s tha

ralative

voLume lavals of

the

LEft

and

Right speakera.

r3.

!1ow_Ett!EE:

Fot

removal of

undeeircd

low fraquancy

materi,a.}

such

as

nrunbJ.er

fron

older

recordinga.

I4.

EI.E!-E!EE.E:

Cute off scratch

from records and

back-

ground

nhiesi

from

noiey Flrl

etationE.

15.

TAPE III]NITOR:

Perrnits monitoring

during

tape racord-

ing.

15.

.[Q!E-EE@L:

Dieablae the

Tonc Controls and auto-

matically

se';s

preanp

responae

charac-

teriatic to

iFlatn.

I7.

LOUDI{ESS COHPENSATION:

Activates

Loudnegs control

comogngation

circuitry.

.I

8.

DYI{AQUAD:

Activatae

Dynaquad

4-channel

Matrix

circuitry.

I9.'I-CHANNEL

ADAPTER:

For connacting

4-chennal decodcr.

Aleo

doublea

aa

gacond

Tapc Monitor.

20.

r4,BE--P!,9E.1U,€,:

Psrnite

racording to, or

playing

back

fron, a

saeond

tapc racorder.

Aleo,

dubbing

fron ona

racordar to ths

othcr.

olo

slEni/ooD

sEL-400

spEctFtcATtoNs.

V

-*

Preomplifier

BA55

COHTROL:

g6dB

0

StlHz

[xith

center

detant].

tilIIrRAt{GE

C0!|TR0L: g6dB

O

9O0Hz

[with

center

detent].

TREBLE

COIITROL:

al6dB

t l5,O00Hz

[rith

centsr

detent].

IiIPUT SEiISITIVITY

(and

IIIPEDAITCE)

e

lOO0Hz:

CR0SSTALK:

Greater than

-40d8,

20-20"000H2.

LtI

FILTER:

3dB Q 45H2, 26dB

g

10H2,

1ZdB/gctave

HIGtf

FILTER:

3dB

O

7O00Hz,

20dB

O

20,000H2,

lAdB/Octave.

TOTAL HARIIOfIIIC

DISTORTION :

Preamplifier

only:

Record Output Amplifier:

Leee than 0.01S

O 2V.

Lese

than 0.01f

O 5V.

Aux

l: 6V.

Aux 2:

5V.

,Tape

ltlonitor:

5V.

4-CH

Adapter: 6V.

FREQUEI{CY

RESPONSE:

Phono

1

&

Phono 2:

3O-15,OO0Hz

glOf.

Aux

I, Aux 2,

l,lic, Tape

l{onitor,

Tape

Ilubbing,

&

4-CH Adapter:

2O-2OrO00Hz

t*dA.

(500

Ohm).

Flaximum Output:5V.

HUf{

ANI} N0I5E:

[signat

to

Noise]

[IHF

"Ao

rdeightins]

\ _

Phono

l:

65dB

75dB-

V

Phono

2:

65dB

75dB

Aux

| &

Aux

2:

80dB

BSdB

Tuner:

80dB

B5dB

Volune

Mininun:

90dB

100d8

*

All specificationa

with

l20VAC

line.

Phono

l:

Phono 2:

llic:

Tuner:

Aux

1:

LO:

Phono

2:

l{ie:

Tuner:

0UTPUT

LEVEL

(and

IHPEIIANCE):

Record

Out:

0

VU, lmu,

775mV

Tape Ilubbing:

tsUmV.

4:-CH

Adapter:

1sthrv.

Preamplifier:

l50mV

(2.2K

Ohm);

Aux 2:

l5&aV

(220K

Ohrn).

Tape

llonitor:

ls{lnrv

(220K

0hrn).

Tape llubbing:

lsthtv

(22OK

Ohsr).

4-CH

Adapterr

l5thV

(220K

Ohn).

II{PUT

CAPABILITY

FoR o.25t

THI}

O

lOooHz:

Phono

|

(rith

Input Sensitivity

Selector

Syitch):

H

I :

gtlmv.

l{EO:

'l

2tlmv.

z.OnV,

4.5nV,

&

g.tlmv

se].actabl'e

(5OK

tlhrr).

z.tlnv

(5OK

Ohn).

2.3rnV

(5OO

Ohn).

't

stlnV

(

22OK ohn).

lslrov

(220K

Ohm).

1zthv.

9tlnv.

9tlrnV.

6v.

Amplifier

PflER &JTPUT

(RilS

rnininum

-

both channele

driven) with no

rore than

9.25*

Total Harmonic

Dietortioni

85 uatte per

channal

O I cihme,

from 20-20r000H2.

9O

ratte

per

channel O I ohne,

1000H2.

120

ratta

per

channel O

4 ohmsl 1000H2.

IHF PflER BAIIIUIIITH:

5-40,t100H2.

IIIPUT SEIISITMTY

(and

IMPEDANCE) O lOtl0Hz:

125nV

(270K

Ohm),

ItAtfIttE

FACT0R:

30

I

ohma, from 20-20,000H2.

Htxr

AilD lroISE:

Signal

to lloise:

90d8.

IHF

rAi

Heighting:

l00dB.

FREQUEXCY

RESP0NSE:

7-100,000H2,

+0d8,

-1d8.

CRIISSTALK:

Greater than

-60d8,

2O-21'BOOHz.

Generolt

PflER

REQUIREMENTS:

l l5-125VAC

,

6OHz.

AC IruTLETs ON CHASSIS:,

Svitched

-

2:

100 watts

maximum each outlet.

Unsritched

-

1:

100 watte

maximum.

RATEI)

PttER CONSUMPTI0N:

35-450

watts.

PfrER FUSE:

5 Amp, 3AG

[Fast

Acting 0n1y].

DII{ENSIONS:

16-9/16

long,

5 high,

14-'l/4

deep.Iinches].

SHIPPING hrlEI6HT:

33 lbs.

Q712

Q711

Q710

0812

Q810

Q811

THERMOsTAT

TM-2

TM-1

PRE-AMP

BD

#es3

3T1

-1

DR IVER

BD

#no33T3-0

vR701

IC

301

TBA231

PR

OTEC

T

I

ON

BD

#es33T5-o

1.-'"

:\r'

VR801

IC

302

rBA231

FIGUR'E

1

(rop

vIE!il

)

SHERL'/OOD

SERV ICE

MANUAL

MODEL

SEL-4OO

AMPLI FIER SERVICE

INFORMATION

\--

v

CONTENTS:

PARTS

L0CATIoNS

Irig.

1]

AMPLIFIER

SERVICING AND

ADJUSTMENT

POIdER

SUPPLY SERVICING

AMPLIFIER ELECTRONIC

RELAY PROTECTION

ORDERING

PART5

PARTS LIST

ISre

SuppIements]

SCHEMATIC

D IAGRAT{

[

See

Supplements

]

CIRCUIT B0ARD C0tIP0NENT

LAY0UT

ISr"

Supplements]

AMPLIFIER

SERVICING AND

ADJUSTMENT:

!.9[E:

1.

For simplicity

only the

]eft

channel

and

its

gre

described. The

right

ci-rannel is identical

except for reference

symbol numberi

Ittt

Schematic

Diagre

For

parts

locations,

refer to

Figure

I

on the inside

covers.

2.

As

a

convience for

fast component location,

this

manual

contains

detailed

pictorials

of all

the

printed

circuit board

assemblies.

Reference

to these

drawings

should

aic

considerably

in

a

quick,

accurate fault analysis

of

an existing malfunction.

USE

OF

A VARIAC:

It is imperative

that

a

variable voltage line

source

fVariac]

equipped

with

a

line

watt-

meter to identify

abnormal pobrer

consumption be used

when servicing

power amplifiers

anc

associated

power

supply circuitry.

With the

Loudness

volume control

set

at minimum,

the

power

consumption should not

exceed 30 watts as the

voltage is increased

by the

Variac

t

the rated

12O

VAC.

If

the

power

consumption begins

to exceed

30

watts,

do NOT

increase

the

line voltage

any

further. Determine if the malfunction

ie in

the

Power

supply,

the

preamplifier

or the

amplifier section of the

unit.

t

Verify that the line fuse is unopened

and

cheek idling

power

consumption.

The

main

caus

for

abnormal powet

consumption, in

order of decreasing

occutancer

ares

l. 0pen ot shorted

amplifier output, driver

or

pre-driver transistors.

2.

Open

or shorted

power

supply diodes.

3.

Shorted

power

transforme!.

AMPLIFIER FAULT

ANALYSIS:

If

an amplifier channel is suspected, check circuit

boards

for

burned

parts

and

replace.

Check all

the

transistors

with

an

ohmmeter for opens

or shorts

and

replace

if

defective.

WARNING:

Some ohmmeters may

damage sensitive

solid-gtate

devices.

Whenever

possiblet

use

a high resistince

ringu

[.t

least

RXl0].

Use

the centerpoint

voltage

Imeasured

from the +

speaker terminal

to

ground] ""

a

guide.

The

centerpoint

voltage should

always

be Zero + 5OmV. Any

deviation

suggests

shorted

or

open deviceso

,

PAGE:

Inside

Covers

1

4

AND SPEAKER

SYSTET'I

CHECKS 4

Back

Cover

\--.

sHERWOOD

SERVICE

MANUAL

If

channel- operation

is still faulty,

verify that there are no

shorted

capacitors, open

besistors, etc.r ort

the board.

Inspect

the

underside of the board

for shorted

pads,

broken connections, etc.

V'Jhen

the board

is

restored,

readjust Output

Bias

Isrr

below].

D I5T_0STI0N

IN AMPLIF

IER

0UTPUT:

Distortion which exceeds

the amplifier

ratings

Is""

Front Cover] r"y be due to the

following:

1. Mismatched output

transistors.

2.

Defective

(low-beta)

driver

transistors.

3.

Incorrectly

adjusted

output

transistor

bias.

OUTPUT

TRANSISTOR BIAS ADJUSTMENT:

Proper output transistor

operation

and output bias adjustment are most

important

to

assure

coo1,

low-distortion operation

of

the amplifier. Bias adjustment is necessary if

the output

transistors

are replaced*,

or if

any

of the

transistors

in the

driver

circuit

or the

amplifier exhibits

one

or more of

the following symptoms:

1.

Overheating

of the output transistors

under

normaL

operating

condi!ions.

(Normal

output

trangisto1: case temperatures are 30-35oC

L82-95oFJ,

quiescent

operati-on

bt

2s

oC

IZe

"r]

ambient.

j

2. Excessive

low

level Intermodulation Distortion

(

tMn)

or

Total Harmonic

Distortion

(fHn)

-

more than 8.1%

at

3.0 volts across

I

ohms.

*

It

is

extremely important that the insulating

washers used to

separate the

output

transistors from

their heat sink be unbroken

and instal-led

properly

with silicon

grease

liberally

applied to all surfaces in

contact with each

other.

Make

certain

the emitter and base

pins

of the output transistors

do not contact

any

part of

the

heat sink assembly.

NOTE:

For the following testsr.an I oh6

load

resistor

must

be connected to

each

of

the

two power

"rptifirr-[Speaker] output terminals.

SUGGESTED

AMPLIFIER TEST

BENCH

SET-UP

SCOPE

I

-J

AUDIO

osc.

SCOPE

B

TO

8rr.

LOAD

OF

AMPLIFIER

VOLTMETER

VARIAC

o-

t60

vo|.Ts

2

D.C.

VOLTMETER

+PROBE

ils- l25VAC

sor

Bffl'sE

ADJ.

TO INPUT

.,ACKS

BEING

REGEIVER

AC

O-3OO

WATTS

sw

mc x

posr

non

Jtt:^:.:tltt'

t.

H.D. MEASUREM-E]{T

t#x

2.

I.M.D MEASUREMENT

VV! '-

3.

SINE

WAVE MEAS.

:6.3VAC

6OdB ATTE

IO

dB

STEPS

\

60Hz

V

Figure 2

\/

\z^

I-'

BIAS ADJUST!4ENT

USING

AN

INTERM.ODULATI0N

DISTORTI,0lrl.

(I..t'|.-D.

)

ANALJZER:

l. Connect the

amplifier

for

testing

as

in

Figure

2.

Connect an

Intermodulation

Distortion

Analyzer with

a

ratio of

421 using 6AHz

and

7000H2

to the

amplifierrs

Left

AUX

1 input

and set

the SELECTOR

switch

io

AUX 1.

3.

Set the

volume

control

to maximum

and

adjust

the

generator

for

an

amplifier

output o

3.0

volts

across

the I

ohm

load of

the amplifier

channel

under test.

4.

While

observing

the

resultant

distortion

waveform,

adjust

the bias

potentiometer

IVnZgt

]

"o that

the

crossover

distortion

is

at

th;

polnt

of

leing

eliminat"J-[ii.""

uABnl.

NOTE:

Class

trAn

operation

[Continued

CCI{

rotation]

causes

the

output

tran

istors to

draw

excessive

current

and

consequently

overheat.

5.

Repeat Steps

3

to 4

for the

Right channel.

Figure

3

Thg

following

performance

indicates

a

properly

operating

amplifier

with both

channels

driven

into I

ohm

loads:

1. Less than 0.1S

fntermodulation

Distortion

Itt{n]

at

3.0V

Itypically

0.05%].

2. 85 watts

of

powex

per

channel

at

no

greater

than

o.zs*

rHD.

BIAs

ApJUSTitENT

UsINE

HARHONIE

D.ISTORTr0N

AtyALJZER:

f.

Cpnnect

the

amplifier

for testing

as

in Figure Z.

2.

Connect

an oscillator

with

}ess than

.O1* distortion at

lKHz to the amplifierts

Left

AUX I

input and

set the SELECT0R

switch

to

AUX i.

3.

Set

the volume

control

to

maximum

and

adjust

the oscillator

for

an amplifier

output

of

3.0

volts across

the I ohm

load of

the

amplifier

channel

under test.

4.

Using

the

Harmonic

Distortion

Analyzerr

looking

at

the

distortion of the

amplifier

properly

nulled,

make

the

adjustment

a9 follgws:

Adjust bias

for Class

rfABrr

operat-

ion

by

turning

the bias potentiometer

[VnZOt ]

=o thal

the crossover

is

at

the

point

of

being

eliminated.

N0TE:

Class

nAi

operation

[continued

CCW

rotation] ".us"s

the output

transistors

to

draw excessive

current and overheat.

Refer to Figure

4

be1ow.

5.

Repeat Steps

3

and

4

for

the

Right

channel.

The following performance

indicates

driven

into I

ohm

loads:

1.

Less than

0.1%

THD at 3.0

2.

90

watts per

channel

at no

3. 85

watts

per

channel

at

no

Proper

Bios

Adiuslmenf

Figure

4

Proper Eios

Adiustment

a

properly

operating

amplifier

volts

Itypically

0.05%].

greater

than

0.25*

THD

ItfH=].

greater

than

O.25*

THD

lZOtlz

with

both channels

lmproper

Bios

Adiustment

lmproper

Bios

Adiuslmcnt

\-'

3-

ZOKHzf.

SHERWOOD

sERVICE

MANUAL

BIAS ADJUSTMENT

USING A LINE

!'/ATTMETER:

When test equipment required

for

not

readily available

and adjustment

is

absolutely

necessarVr

the following

proceedure may be used

which

requires

only

an accurate

line

wattmeter:

1. Turn

the

loudness

control

to

minimum.

2.

Adjust

the bias

potentiometers

(VR701

which the amplifier

begins to cause a

consumption.

POWER

SUPPLY

SERVICING

AND

FAULT ANALYSIS:

& VR801

)

one at a

time to the

point

at

very

slight increase

in line

wattage

Power

supply

malfunctions are

usually due to shorted

or open

power

diodes Xl

-X4,

zt

diodes Z1-25,

transistor

Ql,

or a defective

povrer

transforme!.

The

devices

may be easily

checked with an ohmmeter. The

transformerfs

operation mE

checked

by

measuring

secondary

voltages

with

the

associated circuit

legs

disconneci

AMPLIFIER ELECTRONIC

RELAY PROTECTION

AND SPEAKER

SYSTEM

CHECKS:

It

is absolutely

necessary in

the design of

a high

powered

amplifier

to

provide

Prc

ion for both

the amplifier AND the

speaker load. The

primary

purpose

of the relay

protection

circuit is to disconnect

the

speakers

if

a

potentially damaging situatic

should occur.

If

there

is

no output

to

thg

speaker, first

check

the speaker

connections

for short

wires or

a shorted

speaker

lspeaker

load

resistance

should

not indicate

less

than 4

resistance on an ohmmeterJ. If

the relay

protection

circuit

is

suspect,

the follou

explanation of itls normal

operational characteristics

may

be halpful.

The

complementary darlington

output transistors

are

load line limitedr

with

the ma:,

current limited

to

7.7A

peak

(equivalent

to

1?gW

A 4

ohms).

Signal voltages

develc

across the output transistorfs

emittei resistors

R751 and R752

forward-bias

transis

Q901

and

Q902,

shunting

the output

transistorrs

base drive signal.

The

dual comparator, integrated

circuit

IC901,

and

associated sensing

circuit

is

a

lridge

system_which,

in

effect,

measuxes

the speaker

line

impedance.

fhe

comparatc

Ltett

channelj

Pints

3

and

Z

are biased

so that Pin

3 is

0.3V

positive with

respecl

2. With

this condition,

the comparator

output voltage

is

high

L25UJi

hence,

tl'

bi-stable multivibrator transistors

Q950

and

Q951

activate

the

relay,

connecting

tt

speaker loads to the_amplifier

circuit. Also,

because of

this

turn-on

ndelayn,

the

Power turn-on

pulse

Ispeaker

pops]

are

eliminated.

As the load impedance is reduced,

with

signal applied,

a

point

is reached

where

thi

now rectified signal

(due

to

diodes

X912

&

X940

for the Left

Ehannel,

and

diodes Xt

and X952

for the Right Channel) drives Pip

2-positive

with respect

to Pin 3.

At tt

point

the comparator

output switches

low

LlVJ,

causing the

bi-stable

relay

driver

I

deactivate the relay, disconnecting

the

potentially

dangerous

load

condition.

To

reset the

protection

circuit,

the AC Power

must

be

turned

off for

approximately

seconds before again turning

on the

amplifier.

This

protection

circuit achieves

variable

current limiting,

hence

power

limitingr

t

inverse function of the amplifier load. The

relay

control circuits

are

separately

triggered by each

channel,

but both shut

down simultaneously.

For

example:

Power

t

is

typically

limited to

,|20

watts

@

4

ohms,

9O

watts-E

3 ohms,

4O

watts

g

2

ohms,

t

wattl'E

1 ohm. Normally,

in

a

1

ohm

load

condition

[without

this

patented

variablt

current

limiting syetemJ,

with current limiting

only, the output

transistors

would

required to dissipate 300 watts, resulting

in

their instantaneous

deetruction.

Loudspeaker

protection

is also

provided

in the

event that

either

a

positive ot

negi

DC voltage is developed at the

amplifier speaker

terminals.

Pc,sitive

voltage

protection: An amplifier malfunction

resglting

in

a

positive DC

\

age

at the sprik""

lermiqral

has this voltage

fed

to the

t-]

invirting-input

of coml

lCgOl

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SATE

AS THE LEFT

CHAI{I{EL EXCEPT

FoR AN

tNcREASE 1il

NUMBER|T{c

ay

OTIE HUNDRED

UNLESS OTHERWISE

NOTED.

VOLTAGES:

ALL VOLTA€ES ARE

REF€REI{CED TO

6R0UND

ul{DER tHE FOLLOT|l'tc

COt{0tTtO]{S.

DC:

l.o

SlGllAL

(l2OVAC

LlilEl

AC:

r

'l

AC

STGilAL VOLTAoES AT rXHr, FOR

RATEo

OUTPUT,

r|TH

AN

8

OHT LOAO ATID

VOLUXE COI{TROL

AT TIAX.

lrt

I

ot*o

lovru

T

lorraD

I

'

L___l

I

To

R974

S7

(REToTE

V

.ot

a

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2

l'.,'

o.r o.r

c3ro

=c3r7

.ot

I

.ol

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surce

TT1

z2

l6v

5%

o.4w

c7

93"

:Hi'

@:irl,'

TONE DEFEAT SW.

AO33T2-l

TONE

I

Ao33

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lcSolA

rs

TBA23|

yA739

c5r5

680

I

TIODE

sw.

MODE

sw.

TONE DEFEAT

sw.

TP. MON.

sw.

Jrsol

JI

Boosr

I

R5r7

|

3.31(

r

I

MAIN

AMP/

NORH

SW.

LEFT

CH.

R750

270K

*rf-+

ffl

rli

Erco.€

TP. [Oil.

fftt

rane aNe.

1c530

r

CA3O94AS

c535

lOOrt

tc630

cA3094AS

L-----b*'

---i

ov

L?zq''vlJ

ALL RESISTORS

ME Il1

WATT

TINITUM, IO%

TOLERAICE

UiLE!'! OTIIERlfISE SPECIFIEO.

ALL FRAC?IOIAL.YAIUE

CAPICITORS

ATO ELECTFOLYTICS

ARE

n

,l.

OT{ER CAPACTTORS

ARE

lN

gf.

R'€I{T

CXAXXEL

GOIPOI'EHT

SYI'gOLS AND

VALUES

ARE

THE

SAIE AI THE

LEFT CI.IAI{T{EL

EXCEPT

FOfi AI

ITCREAS€

tT

XUIEERING

BY

OI€

HUTDRED

UILESS

OTXERWISE

IIOTED.

VOLTAGES: ALL VOLIAGES AR€

REFERENCED TO

€ROUtlD

uiD€r THE FOLLoIIX€

COltDtTtOtS.

DC: tro

slcial-

(t2ovac

LINE)

AC:

C I

AC

slcxAl

\,o|-TAGES

AT

IKH!, FOR RATED

OUTPUT.

'ITTI

AII

O

OHI

LOAD ANO

VOLUIE CONTROL

AT TAX.

BCt69

s

169

HEADPHONES

rolto

SPEAKER

XONO

SPEAKER

sw]TcH

R970

t80

2V

ItI.,,".,

lTl

t

I

o4

ECB

ilPSA20

TPSATO

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sPs

5556

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- - - i

,FI,

.'Y<J;

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;::ffi.

lB

RcAlAlo

SHERWOOD

SEL-4OO

STEREO DYNAOUAD

AMPLIFIER

POWER ATP E PROTECTIOI{

SIDE

SER|AL

1{O.

4A4tOOl TO

4A4t550

c^s^o;

i.er

vRsotA

I Mto

EASS

| | tOOr(

SPEAKERS POSITIONS'

swrrcH

t. oFF

I

2.

TAIN

:

sr3

J.REMoTE

I

4.BOTH

,

I

REXOTE

SPEAKERS

+L-

-R+

R974

DRIVER EOARO

:

AO33T3-O

c7ort

420

gF

! Y.1

t:f

lt--

ih:

r

s

Fr

lr\

EE-:

r-

I

R750

270X

cTot

lOrr!

35V

c70l

.oa

I

,l

il

P973

I

't

I

:l

I

.l

,I

0?ll

sJt93e

R72l

47,tmt

c720

ezor

47

3.1:tr

R75r'r2

R7e3

tlx

R724

IK

tc70tB

tov

B6e2xt3-4i

\u

I

L - -- -)+2.8v

r

t2.OV

I R9t2

-2.7Y

c9tl

o.22

c930

o.22

PROTECTION EOARO

R9?9,22X, Jt2U

!

I

b----

----J

\-.'

$tr

(,S'-

*

TONI

tsD

#

nnt33T

2-1

R7s1

It530

CA

3O94AS

IC53O

CA

3O94AS

R7 s2

rr501

rBA231

-::

SW

I

TCH BD

#ao33T4-1

RB51

FIGURE

1

(e0TT0M

VIEW

)

t

SHERbJOOD

SERVICE

MANUAL

MODEL S

in_the

positive

rloltage protection,

the

comparatorts

output

now ewitches

1ow, clamping

off

transistor

Q951,

thereby

deactivating

the relay and

disconnecting

the speaker

1oad.

Thermal- protection:

The

ampJ-ifier

is al-so

protected

against

excessive

and

potentit

.

damaging

temperatures

due to abnormal

load or environmental

conditions.

This

prott

is accomplished

with two

miniature

thermal

switches

Ion"

per amplifier

channell

wh:

are

fastened

to the output

transistors._

When

the output

transistorts

operating

ter

ture

reaehes

approximat'efy

130oC

lZTOofl,

the switch

is thermally activated,

o[enir

itrs contacts,

thereby

diseonnecting

the

AC

line voltage to

the pourer

transformerrt

primary,

a

POhIER OFF

condition.

Jhis

open circuit

condition

now a1'l.ows

the temperr

to

d"9p.__A!

approxinrately

100oC

IZtO"fl

the contacts

close

and

the'"iq,mplifier

retu:

to a

P0WER

0N

condition.

SEDERING

PARTS:

Vr/hen

ordering

replacement

parts, always

include

part

numbers

Isee

Parts

List].

't

I

When

defective

Stations

only]

either

credit

parts

are

returned

for

include

a

list, by part

or replacement parts.

The return of entire

circuit

boards

for replacement

is

except

where component

failure has

reeulted

in

physical

replacement

under

warranty

IAuthorized

Service

number

and

valuer of

the

parts

returned.

Request

IF

normati!

not covered

by wamantV,

damage

to the board

itself.

\.1

\r

If a set or board

cannot

be

repaired,

return

the

complete

amplifier

to

Sherwood

Factory

Service

Laboratoryr

4300

N. California

Ave.

Chicago,

Illinois 60618.

Include

a

conplete

description

of

the

malfunction.

SI{ER\AZOOD

ELEcTRoNTE

LABoRAIoRrEs,

rNC.

rfl

F-

I

st

a

=

c

.rl

\o

\r/

-c

+t

.rl

J

4300 NURTH CALIFoRNIA

AVENUE, CHICAG0,

ILLIN0IS

50618

31

2-478-7300

Sherwood SEL-400 User manual

Sherwood SEL-400 User manual

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