Fisher CA-890 - Recommended Test Equipments; Harmonic Distortion Test

RECOMMENDED TEST EQUIPMENTS
The following test equipments are recommended to completely test and align the Amplifier:
e Line Voltage Isolation Transformer
e AC DC Multimeter
e Accurately Calibrated AC Voltmeter
e Oscilloscope (Flat to 100 kHz Minimum)
e Low-Distortion Audio Sine-Wave Generator
e Harmonic Distortion Analyzer
e Two (2) Load Resistors 8-ohms, 250 Watts
(Minimum Rating)
HARMONIC DISTORTION TEST
CAUTION: Limit the following tests to no more than ten
minutes each. Use 8-ohm resistors, with a minimum
power rating of 250 watts when connecting a load across
the SPEAKERS terminal.
CONTROL SETTINGS:
Unplug the AC power cord and set the front panel
controls as follows:
e POWER switch to the OFF position.
e SPEAKERS switch to the OFF position.
e LOUDNESS CONTOUR switch to the OFF position.
e PARAMETRIC EQ. switch to the DEFEAT position.
e METER RANGE switch to the 200W position.
e TAPE MONITOR switch to the SOURCE position.
HIGH FILTER switch to the OFF position.
SUBSONIC FILTER switch to the OFF position.
MODE switch to the STEREO position.
BALANCE control to the center position.
FUNCTION switch to the AUX position.
VOLUME DOWN button to the MINIMUM position.
LEFT CHANNEL DRIVEN
ONE CHANNEL DRIVEN:
1) Connect a low distortion audio generator to LEFT
AUX IN jack. Set generator frequency to 1 kHz and
output to minimum.
2) Connect an 8-ohm load resistor between SPEAK-
ERS SYSTEM-A LEFT and COM terminals. Connect
a Harmonic Distortion Analyzer and an AC VTVM in
parallel across the 8-ohm load.
83) Connect the AC power cord and set SPEAKERS
switch to ON position. Set the volume level to a
MAX level by Pressing the VOLUME UP button.
4) Increase generator output for 150 Watts RMS (34.6
volts across the 8-ohm load). Harmonic Distortion
Analyzer should measure 0.02 % distortion or less.
5) Repeat steps 1 through 4 for RIGHT CHANNEL.
BOTH CHANNELS DRIVEN
Connect 8-ohm load resistors across LEFT and RIGHT SPEAKERS SYSTEM-A terminals. Adjust
generator output and “VOLUME” control for 150 watts at Left and Right Channels (34.6 volts across
the 8-ohm loads). Harmonic Distortion Analyzer should measure 0.02 % distortion or less at each
channel.
CAUTION:
This precision high-fidelity instrument should be serviced only by qualified
personnel, trained in the repair of transistor equipment and printed circuitry.
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