JBL LSR28P, Техническое и сервисное руководство

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FINAL TEST PROCEDURES
For the final test of the LSR28P, the following check out procedures can be followed. If the
technician measures radically different values for the individual tests, the amplifier should be
troubleshot and repaired to conform to factory specifications.
Power up Test
Verify that the unit to be tested is turned off. Then, connect to a variac with isolated
power supply if possible. Slowly increase the output voltage from the variac, watching
for excessive current drawn. If current is correct (below an 1 amp) verify that the power
led located on the front HF driver is green
Verify the quietness. There should be no hum from the unit.
If there is, this indicates a problem in the internal circuitry and should be checked further
for correct wire wrapping.
Gain Test
Set up the unit as shown on page 11 and verify volume control is turned fully counter
clockwise. Apply a –10 dB input signal and slowly turn the volume control clockwise
noting the signal on the oscilloscope. If the signal is erratic, this will be displayed on the
oscilloscope and indicates a faulty volume control..
Set the frequency on the signal generator to 100 Hz. The LF output level should be
approximately equal to +13 dB +/- 2 dB
Change the frequency to 5 KHz. The HF output level should be approxi5 dB +/-
2dB.
Distortion Test
Set up the unit as shown on page 11. Apply a –10 dB signal to the input and an 8 ohm
load to the output
For the LF amplifier
Increase the voluume control until the LF output is equal to +10 dB. Set the input
frequency around 100 hz and verify the distortion level is below .1%.
For the HF amplifier
Turn the volume control clockwise to an output level of +10 dB. The distortion
level should be under .1% as read on the distortion analyzer.
Rated Power
LF Output
frequency—100 Hz. Input level should be variable from –10 dB to 10 dB with a
2ohm load on output. The onset of clipping should occur at about 130 watts
Hf Output
Frequency—5 Khz, Input level should be variable from –10 dB to 10 dB with an
8 Ohm load on output. The onset of clipping of this amplifier should occur at
about 50 watts
D.C. Offset
Offset should measure 0v +/- 10 mV at the output terminals of either amplifier.