JBL A6000GTi, Руководство по обслуживанию

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137159-1 Rev. 1 A6000GTi Service Manual

2003 Crown Audio, Inc.
Maintenance 4-10
If the voltage is still low, the problem is in the LVPS. Check the gate drive signals into the
mosfets Q50 & Q54 (on Power Supply PWA). Verify that the two mosfets are switching. If
there is a gate drive signal, but no switching, verify that the two drains are connected to
ground thru a 0.04-ohm resistor (R58). If there is still no switching, replace the mosfets and
recheck. If there is no gate drive signal from the pulse width modulator chip (PWM)(U8 on
Power Supply PWA), check the current limit signal on pin 14 of U18. If this signal is high,
there is a problem with the current limit circuit for the LVPS.
ILIM: The ILIM light indicates that either the power supply has drawn too much current, or
that the amplifier has faulted. To determine which is the case, disconnect the ribbon cable
and 6-conductor cable from the amplifier and turn the power supply on by itself. If the
power supply turns on, it is fine.
Reconnect the ribbon cable to the audio section. The audio section faults when dc is
present on the outputs. Check for shorts between the rails and outputs. The most likely
cause of this would be a blown mosfet (Q301-Q308 ch1 and Q401-Q408 ch2) in the audio
section. Check for gate to drain shorts on the mosfets as an indication of a blown part.
Replace the blown components and the gate drive module. Often, when a mosfet blows, it
damages the gate drive, and failure to replace the gate drive will result in more blown
mosfets.
If the ILIM light still lights when the power supply is unplugged from the amplifier, reconnect
the ribbon cable to the audio section, turn the current limit down to 10 amps on +12 supply
powering the unit, and verify the ILIM failure. Check for shorts from the transformer nodes
to battery plus and minus. If necessary, remove the large transformer from the board and
verify the proper switching at the transformer nodes. You should observe 0 to 12-volt
square waves at 500Hz on any of the pads where a transformer lead was connected. If this
still causes an ILIM fault, the most likely cause is a bad power supply mosfet (Q1-Q48).
Measure gate to drain as an indication of a bad part. Replace the bad mosfets and retest.
4.4.2. Audio Section Trouble Shooting
4.4.3. Fault Modes

Over Temp Output devices over 85°C

HF High Frequency oscillations at output

Low Energy Loss of +/-24 volts

VCC Loss of rail voltages

DC/LF DC on the outputs

High average Current Too much time in current limit. Holds audio section off
for 3 seconds, then re-enables.
Over Temp:
Verify that the fans are plugged in and that the airflow path out of the unit is
not blocked.