Fisher 40 Service Manual

Page 1

PRICE $2.00

SERVICE MANUAL 40

; SERIAL NUMBERS
BEGINNING 10001

Two- and Four-Channel Stereo
Home Music Center

WORLD LEADER IN HIGH QUALITY STEREO

Page 2

CONTENTS and SERVICE TIPS

REQUIRED TEST EQUIPMENT
MECHANICAL DISASSEMBLY
DIAL STRINGING

HARMONIC DISTORTION TEST
SIGNAL FLOW

CHASSIS LAYOUT

TUNER ALIGNMENT

TUNER

CONTROL-PREAMP

ooomm-e-wwww

.a

POWER AMP 12

POWER SUPPLY 14

CARTRIDGE PLAYER
FUNCTIONAL OPERATION 16
PREAMPLIFIER 18
ADJUSTMENTS 19
DISASSEMBLY 20
PARTS LIST 21
TROUBLESHOOTING GUIDE 22

CAUTION 3

This precision high-fidelity instrument should be serviced only by qualified personnel,
trained in the repair of transistor equipment and printed circuitry.

Many of these items are included only as a reminder a they
are normal procedures for experienced technicians. Shortcuts
may be taken, but these often cause additional damage to
transistors, circuit components, or printed circuit boards.

SOLDERING: A well-tinned, hot, clean soldering iron tip
will make soldering easier, without causing damage to the
printed circuit board or the components mounted on it.
Regular use of a sponge cleaner will maintain a clean
soldering surface, The heat available at the tip. (not the watt-
age of the iron) is important. Some 50-watt irons reach temA
peretures of 1,0000 F, while others will hardly melt solder.
Smalldiameter tips should be used for single solder con-
nections, pyramid and chisel tips for large areas.

Always disconnect the AC power cord from the line when
soldering. Turning the power switch OFF is not sufficient.
Power-line leakage paths, through the heating elements of the
iron, may destroy transistors.

PARTS REMOVAL: If a part is not being returned for in-
warranty factory replacement, it may be cut in half (with
diagonal cutting pliers) to make removal easier. Multiple
terminal parts, such as lF transformers,or electrolytic capaci-
tors, should be removed using special de-soldering tips made
especially for this purpose. Removing solder from terminals,
reduces the possibility of breaking the printed circuit board
when the part is removed.

ACCIDENTAL SHORTS: A clean working area, free of metal
particles, screws, etc., is an important preventive in avoiding
servicing problems: Screws, removed from the chassis during
servicing, should be stored in a box until needed. While a set
is operating, it takes only an instant for a base-to-collector
short to destroy a transistor (and others direct-coupled to it).
In the time it takes for a dropped screw, washer, or screw«
driver, to contact a pair of terminals (or terminal and chassisl,
a transistor can be ruined.

SOLIDSTATE DEVICES: Integrated Circuits contain the
equivalent of many circuit parts, including transistors, diodes,
resistors, and capacitors. The preferred troubleshooting pro»
cedure requires isolating the trouble to one stage using AC
signal tracing methods. Once the suspected stage is located
the DC voltages at the input and output leads are measured to
give an accurate indication of the operating conditions of the
IC. DO NOT use an ohmmeter, to check continuity with the
IC mounted on the printed circuit board. Forward biasing the
internal junctions within the IC may burn out the transistors.
Do not replace a defective [C until all external resistors,
capacitors, and transformers are checked first, to prevent the
replacement lC from failing immediately due to a defect in
the connecting components. Solder and unsolder each lead
separately using a pliers or other heat sink on the lead to

prevent damage from excessive heat. Check that the leads are
connected to the correct locations on the printed circuit
board before turning the set on.

Whenever possible, a transistor tester should be used to de-
termine the condition of a transistor or diode. Ohmmeter
checks do not provide conclusive data, and many even de-
stroy the junctionlsl within the device.

Never attempt to repair a transistor power amplifier module
until the power supply filter-capacitors are fully discharged.

If an output or driver transistor becomes defective (opens or
shorts), always check ALL direct-coupled transistors and
diodes in that channel. In addition, check the bias pot, and
other parts in the bias network, before installing replacement
transistors. All output and driver transistors in one channel
may be destroyed if the bias network is defective. After parts
replacement, check bias for specified idling current.

in some applications, replacement of transistors must be
made from the same beta group as the original type, The
beta group is indicated by acolored marking on the transistor.
Include this information when ordering replacements

When mounting a replacement power transistor, be sure the
bottom of the flange. mica insulator, and the surface of the
heat sink, are free of foreign matter, Dust and grit will pre-
vent flat contact, reducing heat transfer to the heat sink.
Metallic particles can puncture the insulator, cause a short,
and destroy the transistor,

Silicone grease must be used between the transistor and the
mica insulator and between the mica and the heat sink for
best heat transfer. Use Dow-Corning DIE-3. or an equivalent
compound made for power transistor heat conduction.

Use care when making connections to speakers and output
terminals. To reduce the possibility of shorts, lugs should be
used on the exposed ends, or stranded wire should be tinned
to prevent frayed wire ends,Current in the speakers and out-
put circuitry is quite high - poor contacts. or small wire,
can cause significant power losses, For wire lengths greater
than 30 feet, 16 AWG, or heavier, should be used.

VOLTAGE MEASUREMENTS: All voltages are measured
with the line voltage adjusted to 120 volts. All measured
voltages are t 20%. DC voltages are measured to chassis
with a vTVM, with no signal input unless otherwise noted.
AC signal voltages are measured under the conditions speci
lied on the schematic,

ALIGNMENT PROCEDURES: DO NOT attempt realignment
unless the required test equipment is available, and the align-
ment procedure is thoroughly understood.

© COPYRIGHT 1972 FISHER RADlO ALL RIGHTS RESERVED PRINTED IN U.S.A.

Page 19

ADJUSTMENT

SUGGESTED TEST CARTRIDGES

RCA No. Description

.323 some, full track. at standard recording level,
in a 2-channel cartridge shell.

326 8kHz, full track azimuth alignment, in a 2-
channel cartridge shell.

340 Check for proper head indexing and channel
orientation.

353 3.1 SkHz wow and flutter.

523 Same as 323, in a 4-channel cartridge shell.

526 Same as 326, in a 4-channel cartridge shell.

540 Same as 340, in a A-channel cartridge shell.

554 1kHz, recorded on tracks 2 and 6 at standard
recording level, in a 4~channei cartridge shell.

572 Spot frequency test containing 50Hz, lkHz,

and SK Hz tones

(I8)
AZIMUTH
ALIGNMENT
SCREW

(I33)
CARTRIDGE
MODE
SWITCH

SIO

Order tapes directly from:
RCA RECORDS
Special Products Division
1133 AVENUE OF THE AMERICAS
NEW YORK, N. Y. 10036

SOL ENOID END-STOP ADJUSTM ENT

(1) Insert any 2-CH or 4-CH cartridge. A test cartridge is

not required.

(2) Backout solenoid end-stop adjustment (42) until the
tape head completely stops indexing.

(3) Turn end-stop adjustment in the opposite direction

I turn.

(4) Check operation by indexing head sweral times. Program
lights should advance in the proper sequence.

cs R7

C7

(24)

AC
MICROSWITCH
SIZ

. (IZS)
c WASHER
(UNDER BEARING)

AZIMUTH ALIGNMENT

(1) Connect an AC VTVM to the FRONT-Ft RCDFI OUT
jack and set SELECTOR to CARTRIDGE position. Insert
test cartridge 323 or 523.

(2) Adiust the azimuth alignment screw (18) for maximum
Output. '
(3) Insert test cartridge 326 or 526 and adjust for maximum
output as in step (2).

(4) Lock adjustment screw in place using glyptol, Ioctite,
Duco, or other suitable cement. Be careful to avoid getting
cement on the drive belt.

(42)
SOLENOID
END-STOP

ADJUST

C6

R5, R6

(70)
PREAMPLIFIER
BOARD

19

HEAD HEIGHT ADJUSTMENT

(1) Set BASS and TREBLE controls to minimum. (This
reduces the noise level so that head height may be more
accurately adjusted to reduce crosstalk.) Set SE LECTOR to
CARTRIDGE and MODE/EXT TAPE MONITOR to 4-CH
STE REG.

(2) Connect an AC VTVM to MAIN FRONT-R SPEAKER
terminal and press MAIN SPKRS pushbutton. Insert test
cartridge 554 and press CHANGE pushbutton to play
PROGRAM 2.

(3) Loosen lock nut (52) located on the bottom of cam
bracket (51) and adjust cam shaft (50) for maximum output.
(4) Connect AC VTVM to MAIN FRONT-L SPEAKER
terminal and check output as outlined above.

(5) Reconnect AC VTVM to MAIN FRONT-R SPEAKER
terminal and press CHANGE pushbutton to play PHOG RAM
1. The noise/crosstalk level should be -45dB or better.

PROGRAM
SWITCH SII
(UNDER CAM

BRACKET)

(50)

HEAD
HEIGHT
ADJUST