Crown Studio Reference I Service Manual download pdf (Page 22)

@crown*

Studio

Refer~nce

Service

ManuaE

-..-.-.

-"-

p..-.p

---

, , ,-

R@K

4.7

C@~tr@l

eireuitry

nal.

the outpeat transistorlheatsink

increases

tem-

The

Reference amplifiers

have

fault protect circuitry

Peratu~e, the

ODEP

voltage

kvei

will

drop fmm

guard

against dangerous

voltages

and

turn

on/

+joVBC

f3ear

~~~Cv

If 1s

drop

one of

off

transients,

the

heart

this

~ir~~ifry

the

win-

both

QDEP

vsltages

will

Cause

the

fan

csntroi

sig-

dew

comparator

~102,

?kg

fan

control girc~ij:

moni-

nal to change,

The

fan

contra& signal starts

out

around

tors

the

thermal conditions,

via

the

OBEP

eireuit,

and

-12.5VDC,

3rd

after

complete

ODEP

limiting,

ends

regulates

the

fan

speed

accordingly,

2,5VDC0

Phis

voltage

is fed

into

the inverting

input

the

op-amp

The initial output

4.7,1

DCBF

Pr@t@@

high

$+24V),

and

the

fan

control

signal

becomes

The

amplifier output sigf-ral

passed

through

low

positive,

this output

will

became

low,

thus

turn-

pass filter

(R184,

19,

R186

*and

C107)

the

win-

ing

the

fan

accordin~j~~ The output of

drives

dew

comparator

(UJQ21,

campsnent ex-

U4,

opts-triac,

which

turn

drives

Q4,

triac

ceeds

predetermined level, the output of the

cam-

supply for

fhe

fan,

parator (pins

and

goes

law.

The

result

U302

going

high

state

which

turns

the

muting

Ph@

Gating

Signadis

fed

into

the

nsn-inverting

input

transistors

and

disables

the

high

energy

supply

$he

QP-amP

Uj@+

This

gating signal

p~~duct

opening

the

relay

K2.

Q3,

and

the

Fan

Enable

signal

from

the

display

madule.,

C12

and

RE3

farm

timing circuit that,

4,7,2

Fsuft

Circuit

from the

+15V

supply,

begins

charge,

U1A

rnoni-

The

fau&

circuitry

designed

mute

audio

and

tars

the

tine

voltage

wave

farm

and

Oil

crossing

disa$le the

high

energy

supply

the event of

out-

detector.

Every

lime the

line

waveform crosses

OV,

put

fault.

fau/$

defined

any time

which

the

turned

sa?

and

discharges

C12,

This

causes

ramp-

output

semicsnductars,

both

the

negative

and

posi-

ing

type

waveform.

The

higher

p~$i$ive

portion

.&he

tive

sections, draw excessive currents,

waveform

used

turn

off

%he

~pto-triac,

aven

when

the

fan

contrkal

signat

itself

a value

turn

the

The

[ow

side

&ridge

fault detection consists

Q128,

fan.

Therefare, the

fan cantrod curr~nt

has

duty

cycle,

Q329

and

Q130,

both

NPN

and

PNP

output devices

are

conducting excessive

cajirrents,

tha

output

U'T82

'The

f%f?

Enabje

%nai

cQm@s

from

the

display

!"nod-

(pin

13)

forcegs$

high,

This

disables

the

high

energy

u!@

and

holds the

Gating

Si~flaf

high

when

the

amp&

supply

and

mutes

the

audio

path,

fief

standby<

"I^'herefsfe

the

fan

will

not

turn

when

the amplifier

standby*

The

high

side

bridge

fault

detection

consists

a126,

and

U101.

This

circuit compares the

NPN

and

BNP drive

to the

feedback

signal,

giving

repre-

the

heart

the

power

supply

muiti-tap torraidaH

sentation

output

devics

current.

excessive

cur-

power

transformer,

There

are

two ungrounded, high

wnt

occurs,

the window cegmparatsr

triggered

energy,

secondary

windings,

one

for

each channel,

through the

opto isslatsr

U101.

and

there

one

low voltaga winding

for

the

24V

sup-

plies,

"f?er@

also

thermal

eu%

off

switch

built into

4.1.3

TBFR

Bs%ay

the

transfarmer

wtlich

will

disable the

secondary

wind-

During

power

up,

the

capacitor

C'I

is charging,

ings in

the

event

of the transformer overheating.

which

causes %he

nan-inverting

input

{pin

-4

182

!OW

and

the output

(pin

13)

high,

With

4,8,1

tin@

Filter

high,

the

high

energy

taik

are

disabled by

the

re-

824

and

025

are

ir-t

the

primary,

They

are

wired

lay

K2,

and

the

audio

mutsd

the muting transis-

such

that they

null

out

any

compo9-ren"in

the

tors.

Aft~r

approximately

seconds,

Qis

fully

pawere

This

done

because

the tarriodiat

transformer

charged

and

pulled

high,

thus

causing

may

develop

mechanical

buzz

them

any

low

and

the

amplifier

:,cams

out of

standby-

shift

the

waveform

applied

the

transfarmer

4,7,4

Fsn

Centre!

The

F8n

ContrdSi~na$is

t.aken

from

the

positive

ODE$

bias

valfages.

Both

channel

and

channel

ODEP

inrush current that

possible

with

the

voltages

are

eambined

create

the

fan

c~rrtrsl

sig-

rmer,

SO%$

Start

Circuit

has

been

in-

Circuit

Theov

4-6

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Crown Studio Reference I Service Manual Page 22

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