Fostex B-16 - Page 41

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voltage

is

high,

it

is

adjusted

by

rotating

the

center

slug

of

U5

but

before

doing

this,

check

the

frequency

(lOOKHz,

+0.5KHz)

of

the

erase/bias

master

oscillator.

To

check

the

oscillator

frequency,

the

record/reproduce

amplifier

PCB

is

pulled

out

from

the

b

-16

and

the

frequency

at

connector

pin

No.

4

is

checked.

If

the

oscillator

frequency

is

off

spec,

replace

the

erase/bias

master

oscillator

module

(U15)

.

2)

Record

bias

trap

module,

U9

To

check

bias

leakage

of

TRACK

1,

the

oscilloscope

probe

is

connected

to

TP-5

and

the

probe

ground

clip

to

GND

nearest

to

TP-3.

Put

TRACK

1

in

the

record

mode

and

check

bias

leakage

at

TP-5.

Normal

voltage

is

1.1V

p-p.

If

response

is

off

spec,

check

frequency

(lOOKHz,

±0.5KHz)

of

the

bias/erase

master

oscillator.

Then

rotate

the

center

core

of

U9

to

adjust

bias

leakage.

5.4.5

Erase

current

adjustment

In

adjusting

the

erase

current,

put

the

track

to

be

adjusted

in

the

record

mode

.

To

adjust

TRACK

1,

for

example,

connect

the

hot

side

of

the

oscilloscope

probe

to

TP-4

located

near

REP

CAL,

and

the

ground

clip

of

the

probe

to

GND

pin

at

rear

of

U6,

L.P.F.

Set

the

core

of

L-l

so

that

the

voltage

at

TP-4

is

1,7V

P-P.

Adjust

the

remaining

tracks

2

16

in

the

same

way.

i,

6

Vpp

5.4.6

Bias

current

adjustment

The

track

to

be

adjusted

is

put

in

the

record

mode.

To

adjust

TRACK

1,

for

example,

connect

the

oscilloscope

probe

hot

side

to

TP-2,

Located

near

connector

J-l,

and

the

ground

clip

to

the

GND

pin.

Then,

set

the

BIAS

LVL

trimmer

capacitor

C42

,

150pF,

for

a

level

of

approxi



mately

450mV

p-p.

For

an

accurate

adjustment,

load

a

blank

tape

(Ampex

#456,

Scotch

#226)

on

the

recorder,

record

a

test

signal,

set

the

NR

switch

to

INT,

and

trim

the

BIAS

1VL

trimmer

capacitor

so

that

the

overall

frequency

is

within

3dB

between

250Hz

and

lOKHz,

or

within

5dB

when

the

higher

end

is

14KHz

(measured

at

-2SdB

below

the

reference

level).

During

this

adjustment,

temporarily

set

the

screwdriver

adjusting

slot

of

REC

EQ,

R-106,

2Ki)B

so

that

this

slot

is

parallel

with

the

PCB

plane,

then

trim

it

for

a

flatter

overall

frequency

response.

38

Other manuals for Fostex B-16

Owner's Manual20 pages