Fisher 127 Service Manual

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ervice Manual

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REQUIRED TEST EQUIPMENT

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

Line Voltage Autotrensformer or Voltage Regulator

DC Vacuum Tube Voltohmmeter

Accurately Calibrated AC Vacuum Tube Voltmeter
Oscilloscope ((Flat to 100 kHz Minimum)
Low-Distortion Audio (Sine Wave) Generator
lntermodulation Distortion Analyzer

Harmonic Distortion Analyzer

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

10.7 MHz Sweep Generator

Multiplex Generator (preferably with RF output -
FISHER 300)

455 kHz Sweep Generator

Ferrite Test Loop Stick

2 - Full Range Speakers for Listening Tests

Stereo Source 7 Turntable. Tape Recorder, etc.

Soldering Iron with Small Tip, Fully Insulated from AC Line
Suction Desoldering Tool

CAUTION: This precision high-fidelity instrument should be
sen/iced only by qualified personnel, 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, cléan 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
temperatures of 1,0000 F, while others will hardly melt
solder. Small-diameter tips should be used for single solder
connections, 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
capacitors, 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~coup|ed to it). In the time it takes for a dropped
machine screw, washer, or screwdriver, to contact a pair of
socket 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
[0. DO NOT use an ohmmeter to check continuity with the
it: mounted on the printed circuit board. Forward biasing 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 H: 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

BECAUSE ITS PRODUCTS ARE SUBJECT TO CONTINUOUS IMPROVEMENT, FISHER RADIO CORPORATION RESERVES THE

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 may even destroy
the junctionls) 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 directvcoupled 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, always check the bias adjustment 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. Be sure
to include this information when ordering replacement
transistors.

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
prevent 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 06-3, 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 sized
wire, can cause significant power losses in the system. 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 110%. DC voltages are measured to ground
with a VTVM, with no signal input unless otherwise noted.
AC signal 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
alignment procedure is thoroughly understood.

RIGHT TO MODIFY ANY DESIGN OR SPECIFICATION WITHOUT NOTICE AND WITHOUT INCURRING ANY OBLIGATION.

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REMOVING MOTORBOARD

To gain access to the chassis for servicing, remove the motor
board using the following procedure:

(1) Disconnect AC power cord.

(2) Unscrew the two shipping screws (near the leftvrear and
right-front corners of the turntable baseplate) fully out to lock
the changer to the motorboard.

(3) Remove the six screws in the motorboard andlift the motor-
board at the front. Unplug the two audio cables and the power
plug from the underside of the changer. Remove the four audio
plugs and the power plug from the back of the cassette re
corder. Label the recorder's audio cables with the appropriate
INPUT or OUTPUT designation for easy replacement later.

(4) Remove the motorboard (with recorder and changer
mounted) from the top of the chassis.

(5) To reinstall the motorboard, reverse the procedure. Be

sure to reconnect the audio cables with the red plugs to the
jacks labeled Right.

REMOVING DRESS PANEL

(1) Disconnect AC power cord.

(2) Gently pull the VOLUME, BALANCE, BASS, TREBLE.
SELECTOR, and TUNING knobs off the dress panel control
shafts. Remove the hex nuts from the shafts and remove panel
by pulling forward over the shafts.

(3) Reverse the procedure for reassembly.

DIAL STRINGING

(1) Disconnect AC power cord.

(2) Remove motorboard. Refer to REMOVING MOTOR-
BOARD procedure.

(3) Remove dress panel. Refer to REMOVING DRESS PANEL
procedure.

(4) Prop the unit on its back panel. Remove the two slotted
screws (near the feet) which hold the extension chassis to the
main chassis.

(5) Set the unit on its feet. Lift the extension chassis and pull
fonlvard. Swing the extension chassis away from the main
chassis (at the front) to provide access to the tuning drive
drum.

WARNING: Be careful to avoid breaking the wires intercon-
necting the main chassis and the extension chassis.

(6) Remove the dial pointer from the dial cord.

(7) Rotate the tuning capacitor drive-drum to its maximum CW
position. Loosen the machine screw in the center of the drum
and remove the old dial cord.

(8) Tie end of new dial cord to one end of dial spring. Fasten
to top right ear inside drive~drum. See Figure 1.

(9) Run the dial cord through tht slot in the rim of the drum
and set in the bottom of the outside groove. Guide the dial
cord around pulley "A", across and underneath the tuning
shaft. Wrap 2 full turns (CCW viewed from back) around the
tuning shaft.

(10) Guide the dial cord over pulley 8, across thetront,
around pulley C", and back and around pulley D. Keep
the dial cord taut during this procedure.

(11) Rotate the drive-drum to its maximum CCW position,
allowing the cord to wind onto the drive-drum. Keep the dial
cord taut during this procedure.

SERVICE PROCEDURES

(12) Run the dial cord over the top of the drivedrum (in
inside groove) and into the rim slot. Bring the cord around the
drive-drum ear and place the cord under the beveled washer.
(13) With the machine screw loosened, pull the dial cord
taut and tighten the screw.

(14) Turn the tuning shaft to rotate the drive-drum fully CW
and fully CCW to distribute the tensioning along the dial
cord. Repeat steps (13) and (14) until spring is tensioned.
(15) Place the dial cord over and under the tabs on the

rear of the dial pointer, and place the pointer on the top of
the rail.

(16) Turn the tuning shaft fully CCW. Slide the dial pointer
to zero (0) calibration mark on the logging scale while hold-
ing tuning shaft fully CCW. Cement dial pointer to dial cord
to prevent slippage. Allow cement to thoroughly dry. Check
dial calibration. Refer to FM FRONT END ALIGNMENT.
(17) Reconnect extension chassis. Dress audio cables away
from tuning drivedmm.

(18) Reinstall the dress panel.

(19) Reinstall the motorboard.

REPLACING DIAL LAMPS

(1) Disconnect AC power cord.

(2) Remove dress panel. Refer to REMOVING DRESS PANEL
procedure.

(3) Remove the defective lamp (with its metal shade) from

its bayonet base by pressing the lamp in, and rotating 1/8 turn
CCW. Slide the metal shade off the lamp. Install the re-
placement lamp by pressing in, and turning CW 1/8 turn. Slide
the shade onto the lamp and adjust it to direct the light to:
wards the edge of the dial glass.

(4) Reinstall the dress panel.

REPLACING STEREO BEACON LAMP

(1) Disconnect AC power cord.

(2) Remove motorboard. Refer to REMOVING MOTOR-
BOARD procedure.

(3) Unsolder the two leads from the terminals on the rear of
the STEREO BEACON lamp assembly.

WARNING: Damage to the nylon lamp holder assembly may
result from excessive heating of the terminals. Use a pair of
pliers (as a heat sink) to hold each terminal when soldering
or unsoldering leads.

(4) Gently pry off the nylon lamp holder assembly. Press the
replacement assembly into the mount and resolder the leads
removed previously.

(5) Reinstall the motorboard.

REPLACING METER LAMP

(1) Disconnect AC power cord.

(2) Remove motorboard. Refer to REMOVING MOTOR~
BOARD procedure.

(3) Remove the defective meter lamp (with its metal shade)
from its bayonet base by pressing the lamp in, and rotating
1/8 turn CCW. Slide the shade off the lamp. Install the re
placement lamp by pressing in, and turning CW 1/8 turn.
Slide the shade onto the lamp and adjust it to direct the light
towards the back of the tuning meter.

(4) Reinstall the motorboard.

DRUM FULLV CLOCKWISE

PULLEY

Delve anon EAR

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Figure 1.

REPLACING METER

(1) Remove motorboard. Refer to REMOVING MOTOR-
BOARD procedure.

(2) Unsolder the two leads from the terminals on the rear of
the meter and label each wire with its amoiated pin location
for easy replacement later.

WARNING: Damage to the meter may result from excessive
heating of the meter terminals. Use a pair of pliers (as a heat
sink) to hold each terminal when soldering or unsoldering
leads.

(3) Gently pull the meter retainers away from the rear of the
tuning meter and lift out the meter.

(4) Slide the replacement meter behind the retainers and fit
meter into panel cutout. Resolder the meter leads removed
previously.

(5) Reinstall the motorboard.

REMOVING P.C. BOARDS

To remove a board from its nylon mounts, squeeze the loop
of each mounting clip (using pliers), and lift each corner of

the board. To remount the board, align the mounting holes
over the clips, and press firmly.

CLEANING FRONT PANEL

WARNING: Use only plain lukewarm water for moistening
a freshly laundered, soft lint-free cloth to clean the front
dress panel.

POWER AMPLIFIER CENTER
VOLTAGE TEST

Turn VOLUME control to minimum. Depress MAIN SPKRS
pushbutton switch.

(1) Connect an 8-ohm load resistor across the LEFT SPKRS
MAlN terminals and an 8-ohm load resistor across the RIGHT
SPKRS MAIN terminals.

(2) Connect two 10k 11% resistors in series across capacitor
0953 (1500 uF). Connect the common lead of a Dc VTVM
to the junction of the two resistors.

(3) Connect the probe of the DC VTVM to Test Point 88
(junction of R835 and R837) on left channel of dual channel
power amplifier module. Meter should read 0 volt (11.5 volts).
(4) Connect the probe of the DC VTVM to Test Point 80D
(iunction of R836 and R838) on right channel of power am-
plifier module. Meter should read 0 volt ($1.5 volts).

(5) Disconnect the two 10k resistors.