Adjusting And Calibrating The Power Supply Module - QSC PowerLight Series Technical & Service Manual

Adjusting and calibrating the power supply
module
Adjusting and calibrating the power supply card will help ensure
the success of the repair; this portion of the service bulletin
describes a series of five procedures for doing so. Because of the
specialized nature of the power supply fixture required for these
procedures, it can only be performed at the QSC factory by trained
personnel. Follow these procedures exactly and in order.
There are four trimpots, VR1–VR4 (see Figure 2.14), on the
controller card that must be adjusted correctly before reinstalling
the power supply in the amplifier:
PFC
VR1 On the PL 9.0 , this trimpot sets V
sets V /26.6.
OUT
VR2 This trimpot is for balancing the transformer to the PFC circuitry.
VR3 This trimpot sets the maximum 2-ohm output power. For the
PL 9.0 PFC , it will be set for 4500 watts @ 2 ohms at 2 kHz; for
PFC
the PL 6.0 , it will be set for 3600 watts @ 2 ohms at 2 kHz.
VR4 This trimpot sets the power supply's idle voltage. For the PL
9.0 PFC , it will be set for 191.3 volts DC; for the PL 6.0
be 166.5 volts DC.
VR3
VR4
VR2
Figure 2.15. The locations of the four trimpots, VR1–VR4
Tools and materials needed:
• PFC power supply fixture with external power supply and CMP
(Control-Monitor-Power) box
• Two digital multimeters (DMM #1 and #2) with clip-on leads
• Digital multimeter (DMM #3) with clamp-on AC current probe
• 0–240 VAC Variac™, Powerstat™, or similar variable AC
transformer; 60 amperes or higher rating, with RMS voltage
and current metering
• 120 VAC power (for the fixture's housekeeping supply)
• Four-channel oscilloscope with ×1/×10 probes
• Oscilloscope with differential probe (optional; see
step 10 of the V procedure)
OUT
• Small pocket-type flat-blade screwdriver
• Grounded anti-static work surface
• Audio Precision (AP) workstation with PFC test
procedure files* and 2-ohm load resistor banks
(mimimum power handling capacity: 1250 watts per
8-ohm resistor; 5000 watts total in 2-ohm configura-
tion).
*
The four AP test procedure files are available on the QSC Technical
Support CD-ROM: Pfcxf.tst; Pfcpwr2k.tst; Pfcpwr20.tst; and
Pfctherm.tst.
18
PFC
/32; on the PL 6.0 , it
OUT
PFC it will
VR1
Figure 2.16. The front of the fixture. The amplifier channel's gain control is
to the right, out of the picture
The PFC power supply fixture
The PFC power supply fixture is a special test bed for PowerLight 6.0
and 9.0 supply modules. It has the necessary connections and
indicators for adjusting, calibrating, and testing the modules. It
also contains one audio channel of a PowerLight 9.0 to allow
testing of the module's capability to power an actual amplifier
channel. The fixture is custom built by QSC.
Front panel switches and indicators
From left to right (Figure 2.14):
• Power switch. For the AC lines to the power supply module
being tested.
• Power indicator. It lights when the fixture is connected to AC
power and is turned on.
• Blown fuse indicator. Connected across the large fuse under
the door in the top of the fixture chassis, this indicator will light
if the fuse blows. The fuse, however, is merely a backup in case
the CMP box's solid-state electronic fuse malfunctions.
• Protect, Standby, and Power indicators. In the portions of
the test that use the amplifier channel, these LEDs function just
as they do on a regular amplifier.
• Fan switch. Some portions of these procedures require the
module fans running, and others need them off.
• "Set V " switch. This switch is used for the first procedure.
OUT
• "I " switch. This switch also is used in the first procedure
SET
for checking the module's I
• "I " indicator. This tri-color LED indicates the status of the
SET
module's I circuit.
SET
Rear panel switches and attachments
From left to right (Figure 2.15):
• Audio input. This is where to connect the signal output from
the AP workstation.
• DC high rail outputs. These are two pairs of red and black
binding posts, and they carry the DC output of the supply
module's high rails. Connect DMM #1 to one of these sets of
binding posts.
• Audio output. This Neutrik Speakon connector carries the
audio output of the fixture's amplifier channel. Connect this
circuit.
SET
QSC Audio Products, Inc.
TD-000083-00