Mci Jh-400b series User manual

L

I

;___

I

~

TECHNICAL MANUAL

JH-4008

'·

SERIES CONSOLE

/r

.

\1

'\

. '

I !

,..,

·J

PRINTED

January 1, 1978

MCI, INC.

4007 N.E.

6th

AVENUE

FORT LAUDERDALE,

FLORIDA 33334 USA

TELEPHONE: (305) 566-2853

TELEX: 514

362

MCI FTL

'~

I

'--

-~

I

1...-

I

'

~

INTRODUCTION

Page

1-2

This

SERVICE

AND

REPAIR

manual

supplies

all

of

the

information

needed

to

correctly

operate

and

maintain

a

Series

JH-400B

Console.

The

language

and

the

presentation

of

material

is

as

simple

as

possible,

designed

to

be

quickly

and

accurately

understood

by

anyone

with

a

technical

background.

No

discussion

of

design

problems

or

solutions

is

included,

since

such

information--although

interesting--does

not

contribute

to

the

purpose

of

this

manual.

The

sectional

tabs

allow

quick

location

of

all

sections.

(All

MCI

manuals

are

organized

in

this

same

way.)

Note

that

the

OPERATION

section

gives

a

simplified

explanation

of

the

THEORY

OF

OPERATION.

ALL

unusual

circuits

are

covered

in

detail.

NO

tffiiNTENANCE

or

REPAIR

should

be

attempted~until

this

section

has

been

studied

carefully.

JH-400B

1.0

2.0

3.0

2.1

3.1

3.2

3.3

3.4

I NDEX

INTRODUCTION

INDEX OF

TOPICS

INDEX OF ILLUSTRATIONS

DESCRIPTION

STANDARD

FEATURES

OPERATION

MIKE

MODE

TAPE

MODE

REMIX

MODE

OVERDUBBING

3.

5

SU1-1MARY

3.6

ECHO

SWITCH

3.

7 LIGHT

~1ETER

OPTION

3~7.1

RA~W

GENERATOR

3.7.2

CHANNEL

BOARDS

6.0

TROUBLESHOOTING

7.0

8.0

9.0

10.0

6.1

6.2

6.3

8.1

8.2

8.3

8.4

8.5

8.6

GENERAL

INSTRUCTIONS

SIGNAL SUBSTITUTION

LIGHT

~lliTER

SERVICING

OPTIONS

SPECIFICATIONS

ELECTRONIC

SPECIFICATIONS

MECHANICAL

SPECIFICATIONS

TEST EQUIPMENT

PATCH

BAY

FACILITIES

LIGHT METER

SPECIFICATIONS

JH-50-400B

AUTO~~TION

SPECIFICATIONS

SERVICE

AND

WARRANTY

SCHEMATIC DIAGRAHS

JH-400B

1-2

1-3

1-5

2-1

3-1

3-2

3-3

3-4

3-5

3-9

6-1

6-2

7--1

8-1

8-3

8-4

8-5

8-6

9-1

10-1

Page

1-3

11.0

13.0

Page

1-4

13.1

13.2

SPARE

PARTS

LISTS

11-1

INSTALLATION

13-1

PUNCH

BLOCK

CONNECTIONS

13-1

GROUND

RULES

FOR

GROUNDING

A

RECORDING

SYSTEH

13-1A

JH-400B

I I NDEX

OF

I LLUSTRAT I 0 NS

'--

FIGURE

TITLE

PAGE

1-10

NOT

USED

'--

11

ECHO

SWITCH--BLOCK

DIAGRAM

PRODUCING

FEEDBACK

LOOP

3-4

12

ECHO

SWITCH--BLOCK

DIAGRAM

PRODUCING

NO

FEEDBACK

LOOP

3-5

'~

13

JH-400B

LIGHT

METER

BLOCK

DIAGRAM

3-10

14

JH-400B

FLOW

CHART

3-7

15

MOTHER

BOARD

LOCATION

CHART

6-3

16-19

NOT

USED

20-32

SCHEMATICS INDEX

10-1

JH-400B

Page

1-5

i

'--

DESCRIPTION

I

---

2.0

DESCRIPTION

The

JH-400B

Series

Console

is

an

IN-LINE

console

with

all

of

the

circuits

needed

for

one

complete

MIKE

CHANNEL

and

one

complete

REMIX

CHANNEL

in

each

I/O

module.

Therefore

the

number

of

input/

output

channels

is

completely

flexible.

Any

number

of

I/0

modules--

up

to

the

maximum

for

each

frame--may

be

operated

in

any

console.

If

additional

channels

are

needed,

they

may

be

added

by

simply

plugging

in

new

I/0

modules.

A

proprietary

Op-Amp,

custom

designed

for

optimum

Audio

performance

is

used

throughout

the

console.

In

critical

stages

this

Op~Amp

drives

a

complementary

pair

of

transistors

in

an

output

configur-

ation

which

produces

a

complete

Audio

amplifier

with

very

low

impedance,

low

distortion,

unusually

good

transient

response

and

high

drive

capability.

This

proprietary

Op-Arnp

allows

all

of

the

internal

circuits

in

the

JH-400B

consoles

to

operate

at

OdBv

instead

of

the

usual

-6dBv.

Its

larger

voltage

swing

allows

more

headroom

than

most

consoles

in

spite

of

the

higher

program

level.

With

a

program

level

6db

above

the

usual

level,

the

signal-to-noise

ratio

is

improved

and

the

RF

rejection

on

all

summing

buses

is

improved

by

6db.

The

JH-400B

Series

Consoles

are

supplied

in

two

frame

sizes--

the

JH-428B

and

the

JH-440B.

(Dimensions

are

shown

in

the

Specification

Section.)

The

JH-428B

is

wired

and

tested

for

up

to

28

IiJPUT/OUTPUT

(I/0)

modules

with

five

Console

Control

modules:

1.

A

C01'11'1UNICATION

module.

2.

A

MASTER

module.

3.

A

CONTROL

ROG.r-1

HONITOR

module.

4.

A STUDIO

MONITOR

module.

5:

A STATUS

module.

The

JH-440B

Console

is

wired

and

tested

for

up

to

40

I/0

modules

with

the

same

complement

of

Console

Control

modules.

2.1

STAimARD

FEATURES

Standard

features

for

all

JH-400B

Series

Consoles

include:

1.

Twenty-four

output

buses

are

provided.

2.

Five

Echo

Return

circuits

are

provided.

Four

of

these

circuits

have

full

quad

panning,

and

the

fifth

has

full

channel

assignment

capabilities.

3.

Three

Console

Programming

buttons

are

provided,

which

switch

all

I/0

modules

into

BIKE

mode,

TAPE

mode,

or

REMIX

mode.

JH-400B

Page

2-1

4.

REMIX

mode

outputs

include:

QUAD

~UX

2-MIX

derived

from

the

QUAD

MIX

MONO

~ux

derived

from

the

QUAD

MIX

Two

ECHO

SENDS

Two

CUE

SENDS

All

of

the

above

outputs

are

available

simultaneously.

5.

"Variable

Q"

EQ

circuits

on

each

I/0

module.

The

center

frequencies

of

the

filters

and

the

rolloff

points

of

Shelf

circuits

are

musically

each

other.

A

sufficient

number

of

switch

points

is

provided

to

allow

selection

of

the

exact

amount

of

EQ

required.

Switches

used

for

all

circuits

allow

EXACT

reproduction

of

any

EQ

previously

used.

6.

The

JH-400B

Consoles

are

iJOT

Automation-ready,

since

they

do

not

have

the

VCAs

incorporated

into

the

basic

design.

However,

they

have

been

mechanically

designed

for

easy

installation

of

the

necessary

Fader

Packages.

Automation

is

easy

to

install.

For

a

description

of

the

optional

equipment

available

on

these

Consoles,

see

the

section

on

OPTIONS.

Page

2-2

JH-400B

'

~

OPERATION

---

3.0

OPERATION

I

'-

The

quickest

way

to

become

familiar

with

the

operation

of

the

JH-400B

Series

Console

is

to

study

the

FLOW

CHART

on

page

3-7.

This

chart

shows

the

FUNCTIONS

performed

in

each

module,

and

their

relationship

to

each

other.

Switching,

interconnections,

etc.

are

shown

in

simplified

form.

Functions

ONLY

are

shown.

Programming

controls

for

THREE

MODES

OF

OPERATION

are

supplied

on

the

STATUS

module.

When

these

buttons

are

pressed,

all

I/O

modules

are

switched

into

one

of

the

three

modes.

To

understand

the

three

modes,

it

is

necessary

to

follow

the

signal

flow

when

the

appropriate

relays

are

activated.

3.1 MIKE

f'.10DE

1

'-

Neither

HONITOR

relays

nor

REtUX

relays

are

activated

for

this

mode.

From

the

~UKE

input,

the

signal

flows

through

the

Mike

preamp

to

the

CHANNEL

FADER,

then

through

the

EQ

circuits.

The

CHANNEL

BUS

assignment

switches

come

next.

(Including

the

direct

assign

switch

and

a

feed

to

the

ECHO

switch.)

Each

I/0

module

contains

ONE

CHANNEL

ACN

which

is

the

outout

amplifier

for

the

CH.&~NEL

BUS

having

the

same

number

as

the

I/0

module.

In

addition

to

feeding

the

TAPE

MACHINE

OUTPUT,

this

amplifier

also

feeds

the

~10NITOR

circuits.

(Through

the

MONITOR

relay

contacts.)

The

MONITOR

amplifiers

distribute

the

signal

to

the

CUE

SENDS,

the

ECHO

SENDS,

and

the

QUAD

MIX

BUSES

(via

the

PANNING

controls).

In

this

mode~

the

meters

read

the

output

of

the

CHANNEL

ACN

(which

is

the

TAPE

MACHINE

INPUT

level).

MIKE

mode

is

used

for

setting

up

a

taping

session.

Assignment

of

channels,

recording

levels,

monitor

adjustments,

cue

send

adjustments,

and

echo

send

adjustments

can

all

be

made

in

this

mode.

The

recording

can

be

made

in

either

HIKE

mode

or

in

TAPE

mode.

3,

2

TAPE

~10DE

In

this

mode,

the

MONITOR

relays

are

activated.

REHIX

relays

are

not

activated.

The

Signal

flow

from

the

.HIKE

input

through

the

CHANNEL

FADER,

the

EQ

circuits

and

the

CHANNEL

BUS

assignment

switches

is

the

same

as

it

was

in

HIKE

mode.

The

CHAnNEL

ACN

feeds

the

TAPE

MACHINE

output.

JH-400B

Page

3-1

When

the

MONITOR

relays

are

activated,

the

MONITOR

circuits

get

their

signal

from

the

TAPE

RETURN

input.

The

MONITOR

circuits

feed

the

CUE

SENDS,

the

ECHO

SENDS,

and

the

QUAD

MIX

BUSES

in

the

same

way

they

did

in

HIKE

mode.

In

this

mode,

the

meters

read

the

TAPE

RETURN

level.

The

only

difference

between

MIKE

mode

and

TAPE

mode

is

that

in

MIKE

mode

the

monitors

are

listening

to

the

program

material

BEFORE

it

goes

to

the

TAPE

MACHINE,

while

in

TAPE

mode,

the

.

monitors

are

listening

to

the

program

material

AFTER

it

has

been

sent

to

the

Tape

machine

and

returned

via

the

TAPE

RETURN

line.

NoTE

THAT

THIS

DOES

NOT

MEAN

THAT

YOU

ARE

LISTENING

TO

THE

CHANNEL

AFTER

IT

HAS

BEEN

RECORDED.

THE

TAPE

RETURN

LINE

MONITORS

THE

lfJPUT

TO

THE

TAPE

f'lACHINE DURING

RECQqD

f·10DE.

TAPE

mode

is

normally

used

to

listen

to

what

you

have

recorded

without

having

to

change

the

monitor

mix.

The

monitors

are

fed

from

the

TAPE

RETURN

LINE.

When

the

Tape

machine

is

in

PLAY

mode,

the

TAPE

RETURN

LINE

monitors

the

output

of

the

PLAY

head.

ANY

INDIVIDUAL

1/0

f·10DULE

CAN

BE

SWITCHED

BACK

TO

MIKE

MODE

FROM

TAPE

MODE

BY PRESSING

THE

f'-10N

BUTTON,

THIS

fv1UST

BE

DONE

IN

OVERDUBS

I

NG,

(The

MON

button

releases

the

MONITOR

relay.)

3I 3 RH1I X

~-10DE

In

this

mode,

BOTH

the

MO~UTOR

relays

and

the

REMIX

relays

are

activated.

The

REMIX

relay

switches

out

the

Mike

input

and

connects

the

TAPE

RETURN

INPU'ifl

to

the

CHANNEL

FADER.

The

EQ

circuits

and

the

CHANNEL

BUS

and

the

CHANNEL

ASSIGNMENT

structure

is

being

fed

from

the

TAPE

RETURN.

The

EQ

output

also

feeds

(through

the

REMIX

relay

contacts)

the

MONITOR

circuits.

CUE

SENDS,

ECHO

SENDS,

and

the

QUAD

lUX

BUSES

are

all

fed

from

the

output

of

the

EQ.

Note

that

the

TAPE

~~CHINE

OUTPUT

terminals

are

live,

and

may

be

used

as

additional

SENDS.

In

this

mode,

the

meters

read

the

TAPE

RETUR~

level.

ANY

INDIVIDUAL

1/0

r10DULE

CAN

BE

St•JITCHED

BACK

TO

TAPE

MODE

FR0~1

REMIX

MODE

BY

PRESSING

THE

FDR

BUTTON.

TO

SWITCH

THE

MODULE

FROM

REMIX

MODE

TO

MIKE

MODE,

PRESS

BOTH

THE

FDR

BUTTON

AND

THE

MON

BUTTON,

(The

FDR

button

releases

the

REMIX

relay,

the

MON

button

releases

the

MONITOR

relay.)

Page

3-2

JH-400B

--

1

NOTE:

In

REMIX

mode

the

rotary

MONITOR

FADER

has

no

control

over

the

monitor

level.

The

CHANNEL

linear

fader

controls

the

monitor

level.

When

the

FDR

switch

is

pressed

on

any

modules,

changing

that

module

back

to

TAPE

mode,

the

rotary

MONITOR

FADER

again

has

control

of

the

MONITOR

level.

The

CHANNEL

linear

fader

no

longer

has

control

of

the

monitors.

REMIX

mode

is

used

to

combine

the

outputs

of

the

multitrack

recorder

into

the

final

tracks

to

be

used

in

making

the

record.

3.4

OVERDUBBING

TAPE

mode

is

normally

used

for

overdubbing.

The

multitrack

machine

must

be

in

CUE

(sync)

mode

(Record

head

being

used

for

playback).

At

the

moment

when

the

OVERDUB

is

to

begin,

the

tracks

to

be

re-

recorded

must

be

put

into

RECORD

mode.

The

console

mode

will

not

need

to

be

changed.

When

the

OVERDUB

is

complete,

the

only

change

needed

is

to

switch

the

tape

machine

back

to

PLAY

mode.

3I 5

SUMt·1ARY

MIKE

mode

occurs

when

both

the

MONITOR

relays

and

the

REMIX

relays

are

inactive.

This

mode

is

used

for

preliminary

setup

and

for

taping.

TAPE

mode

occurs

when

the

MONITOR

relays

are

activated,

and

the

REMIX

relays

are

NOT

activated.

This

mode

is

used

for

taping,

for

listening

to

recorded

material,

and

for

overdubbing.

Any

individual

channel

which

is

in

TAPE

mode

may

be

returned

to

MIKE

mode

by

pressing

the

HON

button

(releasing

the

MONITOR

relay).

REMIX

mode

occurs

when

BOTH

the

MONITOR

relays

and

the

REtUX

relays

are

activated.

This

mode

is

used

for

tUXDOWN

functions.

Any

individual

channel

which

is

in

REHIX

mode

can

be

returned

to

TAPE mode

by

pressing

the

FDR

button

(releasing

the

REMIX

relay).

Any

individual

channel

which

is

in

REMIX

mode

can

be

returned

to

MIKE

mode

by

pressing

BOTH

the

FDR

button

and

the

MON

button

(releasing

BOTH

the

REMIX

relay

and

the

MONITOR

relay).

JH-400B

Page

3-3

3.6

ECHO

SWIT,CH

In

REMIX

MODE,

the

ECHO

switch

is

a PRE

(fader)

-POST (EQ)

selector

for

the

input

to

ECHO

SEND

#1.

In

MIKE

or

'l'APE

mode,

the

ECHO

switch

is

used

as

a "WET"

switch

to

allow

ECHO

~o

be

recorded

on

the

MASTER

TAPE~

When

recording

ECHO,

~

feedback

loop

may

be

formed

unless

the

FEED POINT

to

the

ECHO

SEND

is

chosen

carefully.

The

following

BLOCK

DIAGRAMS

show

the

problem

and

the

solution:

Assign

Sw.

Channels

Buses

Pream12

1--~-tl-

-o--

&

EQ -

~c:>----'\JV\r

--=-~

'!'ape

>--e----~Recorder

Figure

11

Page

3-4

This

arrangement

produces

a

feedback

loop.

JH-400B

ECHO

Chamber

--

-

[

L

I

I..-

L

[

,_

3.7

-

!

I

'--

Preamp

&

~~----{

EQ

Figure

12

Assign

Sw.

LIGHT

METER

OPTION

Channel

Buses

Tape

>--.~--------~Recorder

ECHO

1--~---t

Chamber

No

feedback

loop

is

produced

by

this

arrangement.

The

JH-400B

LIGH,T~·1<1ETER

uses

a

separate

POWER

SUPPLY,

a

MASTER

COJ:·JTROL

BOARD,

and.v

qne

CHANNEL

BOARD

for

each

meter.

....

~·

,,~

The

MASTER

CONTROL BOARD

generates

the

precision

RA~1P

which.

is

used

on

each

CHANNEL

BOARD

to

measure

the

AUDIO

SIGNAL

LEVEL.

(See

the

LIGHT

METER

BLOCK DIAGRAM

on

page

3-10)

.

Each

CHANNEL BOARD

controls

a

set

of

eight

lights

which

display

the

level

of

the

AUDIO

SIGNAL

in

one

channel.

JH-400B

Page

3-5

3.7.1

RAMP

GENERATOR

(See

Schematic,

Figure

29,

Page

10-21)

Two

"one

shot"

multivibrators

alternately

trigger

each

other

and

clock

a

BCD

COU~JTER

through

each

step

from

0000

to

1001

(0

through

9),

resets,

then

repeats

the

sequence.

The

counter

drives

a

BCD

TO

DECIMAL

DECODER

whose

decimal

outputs

go

LOW

as

the

equivalent

binary

input

is

fed

to

it.

The

DECODER

drives

a D/A

(Digital

to

Analog)

CONVERTER

which

is

contoured

to

produce

a

logarithmic

change

in

ten

steps.

The

VOLTAGE

DIVIDER,

R3-Rl2,

feeds

a

signal

voltage

to

IC5

which

varies

from

+15

volts

to

+7.5

volts,

depending

on

which

output

of

the

DECODER

is

?Ulled

to

ground

potential.

The

RA~1P

output

is

a

positive-going,

15

volt,

10

step,

logarithmic

shaped

wave,

with

a

repetition

rate

of

about

5

to

6

kHz.

The

BCD

information

developed

by

the

COUNTER

·is

also

fed

into

buses

to

be

used

by

all

of

the

Channel

Cards.

3.7.2

CHANNEL

BOARDS

(See

Schematic,

Figure28,

Page

10-19)

The

incoming

AUDIO

SIGHAL

is

rectified

and

filtered

to

produce

a

changing

DC

voltage

which

is

equivalent

to

the

AUDIO

LEVEL.

This

level

is

compared

to

the

RAMP

coming

from

the

MASTER

CONTROL

BOARD.

When

the

RAMP

exceeds

the

AUDIO SIGNAL

level,

the

cm1PARATOR

output

switches

to

the

positive

rail

and

sends

a

signal

to

the

QUAD

LATCH.

The

QUAD

LATCH

receives

as

its

input

signal,

BCD

information

from

the

MASTER

CO~TROL

BOARD.

This

BCD

information

is

IN

STEP

with

the

RAMP

(since

the

BCD

drives

the

D/A

converter

which

produces

the

RAMP).

When

the

COHPARATOR

switches,

the

QUAD

LATCH

is

clocked,

and

its

cutout

matches

the

input

it

is

receiving

at

the

moment.

NOTE:

The

QUAD

LATCH

CLOCK

works

ONLY

on

the

POSITIVE-GOING

EDGE

of

the

signal

•

It

will

not

resp:::>nd

to

either

a

HI

level

or

a

LO

level

signal.

The

DIGITAL

"WORD"

on

the

out?Ut

of

the

QUAD

LATCH

is

held

until

a

new

CLOCK

PULSE

is

received

from

the

COMPARATOR.

The

output

of

the

QUAD

LATCH

drives

a

BCD

TO

DECIMAL

DECODER.

The

decimal

output

corresponding

to

the

digital

"WORD"

goes

to

ground

potential

and

turns

ON

its

light.

NOTE:

Outputs

corresponding

to

"0"

and

"1"

have

not

been

supplied

with

a

light·

This

means

that

the

DISPLAY

is

unlighted

when

the

AUDIO

SIGNAL

is

at

its

lowest

level.

A

NEW

LEVEL

COMPARISON

IS

COMPLETED

EVERY

0.2

MILLISECONDS,

JH-400B

Page

3-9

--

-- -

--

----

-·-

-

Clock

i

BCD

to

Counter

Decimal

Decoder

MASTER

CONTROL

BOARD

(4Cl43)

-----------l

D/A

Counter

l RAMP

OUTPUT

:...._____j[>·

>-------4

BCD

0

OUTPUT

I

L

____

_

-------------

- - - - - -

·-

··- - - - - _J

r-

'

I

RAMP

INPUT

AUDIO

J;NPUT

BCD

INPUT

----------------

Precision

I

Rectifier

Comparator

--------------,

l

!

Latch

I

~----------j

,..-1---l..------L,

Decoder

I

i

'

I

L

________

_

----------------------

_j

CHANNEL

BOARD

(4Cl38)

Figure

13

BLOCK

DIAGRAM

JH-400B

LIGHT

METER

L L

TROUBLESHOOTING

6.0

TROUBLESHOOTI~S

6,1

GENERAL

INSTRUCTIONS

Host

of

the

process

of

troubleshooting

the

JH-400B

COUSOLE

can

be

accomplished

through

the

PATCH

BAY.

The

process

is

called

PROGRESSIVE ISOLATION,

and

use

the

FLOW

CHART,

page

3-7

as

a

guide.

The

FLOW

CHART

is

your

most

reliable

guide

to

the

relative

positions

of

the

PATCH

POINTS

and

the

FUNCTIONS

found

in

each

module.

With

proper

use

of

the

built-in

signal

generator,

the

patch

bay,

and

the

flow

chart,

you

should

be

able

to

isolate

any

problem

within

a

few

components

before

you

remove

a

single

panel.

There

are

two

preliminary

steps

which

are

important

enough

to

be

called

RULES

to

be

followed

BEFORE

you

start

troubleshooting~

1.

FAMILIARIZE YOURSELF

with

the

SIGNAL

FLOW

in

the

console.

A.

There

are

THREE

!10DES

of

operation

in

the

JH-400B.

They

are

fully

explained

on

pages

3-1

through

3-3

of

this

manual.

FOLLOW

THE

SIGNAL

FLOW

FOR

EACH

MODE,

B.

Be

sure

that

you

know

the

ORDER

in

which

the

signal

passes

through

each

FUNCTION.

{i.e.-

Channel

Fader,

EQ

circuit,

Pan

controls,

etc.)

2.

FA~ULI~RI

ZE

YOURSELF

with

the

position

of

each

PATCH

POINT.

A.

Patch

Bay

information

is

available

on

page

8-5

of

this

manual.

B.

The

FLOW

CHART

on

page

3-7

shows

the

position

of

each

patch

point

-

LOCATED

ON

THE

SIGNAL PATH.

EVERYTHING

NEEDED

TO

PREPARE

YOURSELF

TO

LOCATE

TROUBLE

IN

THE

CONSOLE

IS

AVAILABLE

IN

THIS

t'iANUAL.

6.2

SIGNAL

SUBSTITUTION

A.

Use

the

AUDIO

GENERATOR

located

in

the

CO~ll1

module

as

a

signal

source.

The

"TRI<S"

and

"~UX"

switches

on

this

module

connect

the

signal

to

the

Channel

Buses,

or

to

the

Quad

aix

Buses.

You

may

also

pick

up

this

signal

at

the

"OSC"

jack

in

the

Patch

Bay.

B.

USE

THE

FLOW

CHART

to

follow

the

signal

flow

through

the

console.

LOCATE

THE

SPECIFIC

SECTION

where

the

signal

is

lost.

JH-400B

Page

6-1

',iii>c:~·f).

>,

.

..,

6.3

LIGHT

METER

SERVICING

c

The

LIGHT

METER

is

basically

a DIGITAL

instrument,

and

must

be

thoroughly

understood

before

any

servicing

is

attem9ted.

a

detailed

explanation

is

given

on

pages

3-9

and

3-10

of

this

manual.

Adjustments

and

calibration

procedure

is

as

follows:

1.

With

all

light

meters

and

the

Haster

Board

plugged

in,

verify

that

the

logic

supply

is

Sv

+0.2v

on

the

Mother

Board.

2.

Check

the

+

15v

supply

to

the

!-1other

Board.

3.

Depress

the

HOLD

but

ton

on

the

Has

ter

Board

and

measure

the

voltage

on

the

RA~1P

bus.

Adjust

the

OFFSET

pot,

Rl6,

for

-0

.1

v.

(Channel

Boards

adjacent

to

the

Master

Board

may

have

to

be

removed

to

get

at

the

OFFSET

p::;t.)

Set

the

OSCILLATOR

output

for

+4

dBv

at

1

kHz.

Assign

to

"TRKS".

Set

console

to

"MII\E"

mode.

4.

Adjust

the

oscillator

level

for

+4

dBv

output

level

at

the

channel

line

output

of

the

channel

being

calibrated.

5.

Connect

an

oscilloscope

to

6

of

IC2

on

the

Channel

Board

being

calibrated.

This

is

the

output

of

a

full

wave

precision

rectifier.

Adjust

R6

for

a

symmetrical

waveforem.

6.

Place

the

Channel

Board

in

VU

mode.

Adjust

the

level

pot,

Rl,

for

"0"

VU

display

on

the

light

meter.

("0''

vu

is

indicated

when

"0"

VU

level

lamp

just

lights

up).

7.

Repeat

steps

4,5,&

6

for

each

Channel

Board.

8 .

9.

After

all

the

channels

have

been

calibrated,

key

the

ON

and

OFF

with

the

"TRKS"

switch.

Observe

the

rise

time

on

the

display.

They

should

all

be

identical.

ARE

DIFFERENT, REPEAT STEP

5.

oscillator

and

fall

IF

THEY

[:

1

Page

Switch

the

channel

cards

from

VU

mode

to

PEN<

mode

and

again

key

the

oscillator

Oi-J

and

OFF

with

the

"TRKS"

switch.

Observe

that

all

meters

display

the

level

instantly

and

decay

in

two

seconds

when

the

oscillator

is

turned

OFF.

6-2

JH-400B

MCi JH-400B Series User manual

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