Marantz 250 - Maximum Power Output Testing; Relay Operation Verification; Harmonic Distortion Measurement; Output Short Circuit Test

Maximum Power Output
1. Connect the audio oscillator to the input
jacks of the Model 250. Set the audio
oscillator frequency to 20 KHz.
2. Connect the distortion analyzer across
the Channel A output load (4 ohms), set
the analyzer on the 30 vac scale.
3. Turn the amplifier board potentiometers
R541 and R542 fully CCW.
4. Turn Line Switch to ON. Turn the ana-
lyzer and audio generator to ON. Increase
the audio oscillator output until the ana-
lyzer indicates 25.5 vac.
5. Adjust potentiometer R541 clockwise
until the positive peak of the waveform,
as observed on the oscilloscope, just be-
gins to clip.
6. Adjust potentiometer R542 clockwise
until the negative peak just begins to clip.
7. Change output load to 8 ohms. Set ana-
lyzer sequentially to 20 Hz, 2 KHz, and
20 KHz. Output voltage should not be
less than 31.6 volts.
8. Turn Line Switch to OFF. Arrange
setup for Channel B and repeat steps 4
through 7.
Relay Operation
1. Turn Line Switch to OFF. Wait approxi-
mately 2 minutes.
2. Turn Line Switch to ON. The elapsed
time between the instant the power is
applied until the relay energizes should
be between two and ten seconds.
3. Set Audio Oscillator to 4 Hz with output
reduced to minimum.
4. Increase Audio Oscillator output slowly,
watching the voltmeter. The relay should
de-energize between 15 and 32 volts.
Harmonic Distortion Test
1. Set Audio Oscillator frequency to 20 Hz
and adjust level for 31.6V output. Set
Distortion Analyzer to SET LEVEL —
MANUAL mode. Adjust sensitivity for
full scale reading on 0-1 scale.
2. Switch Distortion Analyzer to DISTOR-
TION mode and monitor Channel A out-
put. Total harmonic distortion should
be no greater than 0.1%.
3. Repeat test for Channel A with Audio
Oscillator frequency set at 20 KHz.
4, Repeat test for Channel A at 20 Hz and
20 KHz with 0.5 MFD across load. Total
harmonic distortion should not exceed
0.15%, Verify absence of parasitic oscil-
lation.
5. Perform steps 2, 3, and 4 for Channel B.
Short Circuit Test
CAUTION: Do not per-
form this test if amplifier
shows any sign of para-
sitic oscillation.
1. With amplifier working into an 8 ohm
load, set Audio Oscillator level to 22 volts
at 200 Hz.
2. Short out each channel with Ammeter.
Reading should not exceed 9.5 amperes.
Frequency Response Test
1. Using 8 ohm load and Audio Oscillator
level at 30 volts, sweep frequency from
20 Hz through 20 KHz.
2. Output voltage should stay between
29.7 vac and 30.3 vac
Meter Calibration Procedure
1. Set the frequency of the audio oscillator
to 1 KHz. Connect oscillator to CHAN-
NEL A input jack. Connect analyzer to
CHANNEL A output terminal.