Fisher 201 Service Manual

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SERVICE MANUAL

The Fisher;
201

, Stereophonic AM-FM Receiver

WORLD LEADER IN HIGH QUALITY STEREO

PRICE $1.00

0

SERIAL NUMBERS
BEGINNING 50001

N
.A

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TEST EQUIPMENT and SERVICE TIPS

The following equipment is required to completely test and align modern high-fidelity amplifiers, tuners, and receivers.

Line Voltage Autotransformer or Voltage Regulator

- DC Vacuum Tube Voltohmrneter

o Accurately Calibrated AC Vacuum Tube Voltmeter

. Oscilloscope (Flat to 100 KHz Minimum)

. Low-Distortion Audio (Sine Wave) Generator

0 lntermodulation Distortion Analyzer

- Harmonic Distortion Analyzer

- 2 - Load resistors, 8-Ohms, 100 Watt (Minimum Ratingl
- AM/FM Signal Generator

10.7 MHz Sweep Generator
Multiplex Generator
(preferably with RF output)
455 kHz Sweep Generator
Ferrite Test Loop Stick
2 7 Full Range Speakers for Listening Tests
Stereo Source - Turntable, Tape Recorder, etc.
Soldering Iron with Small Ti , Fully Insulated from AC Line
Suction Desoldering Tool

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

Many of these items are included only as a reminder - 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 tem
peratures of 1,0000 F, while others will hardly melt solder.
Smallrdiarneter 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 element 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 IF 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 baseto-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 chassis),
a transistor can be ruined,

SOLID-STATE 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
ICt DO NOT use an ohmmeter to check continuity with the
EC mounted on the printed circuit boar . Forward biasin the
internal junctions within the IC may burn out the transistors.
Do not replace a defective lC until all external resistors,
capacitors, and transformers are checked first, to prevent the
replacement IC 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 destroy
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 it 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 a colored 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 DC-S, 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 7 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 i 10%, DC voltages are measured to ground with
a VTVM, with no signal input unless otherwise noted. AC sig»
rial voltages are measured under the conditions specified on
the schematic.

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

@COPYRIGHT1971 FISHER RADIO ALL RIGHTS RESERVED PRINTED IN U.S.A.

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4 DIAL STRINGING

HARMONIC DISTORTION TEST

PULLEY

DlAL STRINGING

(1) Remove screws securing top and bottom covers to receiver
chassis. Remove covers. Unsnap pointer from its sliding
carrier. Remove carrier from the rail,

(2) Rotate tuning drum fully clockwise.

(3) Remove old dial cord. Be careful not to remove dial spring
from its ear in the drum.

(4) Tie end of new cord to end of dial springi Make sure that
dial spring is fastened to tuning drum as shown in the figure.
(5) Guide dial cord through rim slot and Wind a full turn
around drum. Guide cord around pulleys A, B, and C and over
pulley E. Wind dial cord three times around tuning shaft and

PULLEY

PULLEY

®

DETAlL FOR
DlAL POlNTER
STRlNGlNG

INS 522

over pulley D. Wind cord 3/4 turn around tuning drum and
through rimslot.

(6) Pull dial cord taut and hook cord to end of dial spring.
(7) Rotate tuning drum clockwise and counterclockwise to
distribute the tensioning.

(8) Repeat steps (5) and (7) until spring is tensioned. Then
tie dial cord securely to end of spring.

(9) Place dial cord over and under tabs on pointer carrier (see
figure). Snap pointer into sliding carrier.

(10) Turn tuning drum fully counterclockwise, Slide pointer
to indicate zero on tuning dial while holding tuning drum
fully counterclockwise

(11) Check dial calibration. Refer to FM/AM ALIGNMENT.

HARMONIC DISTORTION TEST

CAUTION:

(A) Measure the power of one channel at a time.

(B) Limit measurements to 10 minutes.

(C) Use a load resistor with a minimum rating otASO watts.

(1) Set BASS and TREBLE controls to flat (0), SELECTOR
switch to AUX 1, and POWER/SPKRS switch to AC OFF.
(2) Connect a lowidistortion sine wave signal generator
between L AUX 1 IN jack and chassis ground. Set the signal
generatortrequency tolOOOl-lz and output level to minimum.

(3) Connect the 8v0hm load resistor between L MAIN SPKR
and COM terminals. Connect an AC VTVM, oscilloscope, and
harmonic distortion analyzer across the 8-ohm load resistor.
l4) SEt POWER/SPKRS switch to MAIN. Turn VOLUME
control slowly to maximum.

(5) Adjust the signal generator output until the AC VTVM
indicates 12.6V RMS (20 watts). The HD analyzer should
indicate less than 1% harmonic distortion.

(6) Repeat steps (1) through (5) for the right channel.