Calibrations; Amplifier Power Up; Dc Offset Adjustment; Overlap Correction - JBL A6000GTi Service Manual

137159-1 Rev. 1
Procedure Parallel Mode: Load the amplifier with 1 ohm from Ch1+ to Ch1-. Place a
jumper from Ch1+ to Ch2-. Inject a 100 Hz signal. Increase the input until the output
reaches 77.5 volts. THD should be less then 0.1%.

4.7. Calibrations

4.7.1.

Amplifier Power up:

Connect ribbon cable and 6-conductor cable from power supply to audio section (taking
care to drain the rail voltages before connecting). Adjust the current limit on the external
power supply to 20 amps dc. Disconnect all input signals from the amplifier. Apply 5 volts
to the REM terminal. The unit should draw approximately 12 amps when the power supply
and audio section are both on and working correctly.
4.7.2.

DC offset adjustment:

Measure the DC offset on each channel. This level can be adjusted on for channel 1 by
turning potentiometer R115 on the input board. For channel 2, use potentiometer R215.
Adjust the levels, if necessary, to less then 5mV per channel.
4.7.3.

Overlap correction:

Connect probes to TP1 & TP3 on the coil board. Center the oscilloscope to measure the
lower right portion of square wave. Adjust the time scale to 50ns per division. Adjust R307
for channel 1, and R407 for channel 2. Turn the potentiometer so that the transition zone
on the corner of the waveform is less then 10 volts.
4.7.4.

Current Monitor adjustment:

Connect a 2 ohm load to each channel. Inject a 100Hz sine wave into the amplifier. Adjust
the sensitivity until the amplifier output is 10Vrms. Adjust R631 on the outer front-end
board while monitoring TP306 on the main board. Adjust the potentiometer so that the
voltage on TP306 is 1Vrms. Repeat for channel 2 with R361 on the inner front-end board
and TP406.
2003 Crown Audio, Inc.
A6000GTi Service Manual
Maintenance 4-14