Fisher CD 4 Service Manual

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The Fisher ®
_C D-4 DEMODULATOR
C HASS'S

INSTALLATION AND
SERVICE MANUAL

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1 WORLD LEADER IN HIGH QUALITY STEREO

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TEST EQUIPMENT and SERVICE TIPS

The following equipment is required to completely test and align the CD-4 demodulator:

O Line Voltage Autotransformer or Voltage Regulator
0 DC Vacuum Tube Voltohmmeter

O Accurately Calibrated AC Vacuum Tube Voltmeter.
0 Oscilloscope

0 Low-Distortion Audio Oscillator

0 CD-4 Generator (Fisher 3109)

0 RCA Shorting Plugs (2)
0 47inch jumper with alligator clips

10 UP Electrolytic Capacitor

Soldering Iron with Small Tip,

Fully Insulated from AC Line

Suction Desoldering Tool

IONI This precision high-fidelity instrument should be serviced only by qualified personnel,
AUT a 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.

SOLDERlNG: A wellatinned, 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 wrll 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 wrll hardly melt solder.
Small-diameter 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: lf 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 tie-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
servicrng 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-toAcollector
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.

COPYRIGHT 197 FISHER RADIO 0 All Rights Reserved.

SOLlD-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
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 IC 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 destroy
the junctionlsl within the device.

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.

VOLTAGE MEASUREMENTS: All voltages are measured
With the line voltage adjusted to 120 volts. All measured
voltages are 1-. 10%. DC voltages are measured to ground with
a VTVM, with no signal input unless otherwise noted. AC sig-
nal voltages are measured under the conditions specified on
the schematic.

ALlGNMENT PROCEDURES: DO NOT attempt realignment
unless the required test equipment is available, and the align»
merit procedure is thoroughly understood.