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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
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
related
circuitry
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.
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
previous
bias adjustments is
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
Pin
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-]
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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,
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4300 NURTH CALIFoRNIA
AVENUE, CHICAG0,
ILLIN0IS
50618
31
2-478-7300
/