QSC PowerLight Series, Technical & Service Manual

Page: 23 / 100

Technical Service Manual 21
PowerLight 6.0 II, PowerLight 6.0 PFC , and PowerLight 9.0 PFC
Procedure 3 of 5: Adjusting transformer balance
This is done in three stages. In the first two, watch the trans-
former flux “bubble” waveform on the oscilloscope, and on the
third, adjust the AC current to a minimum. To prevent overcurrent
cutback due to undervoltage, adjust the Variac to 130 volts for
120-volt modules or 260 volts for 230-volt modules.
1.
Set the CMP box’s electronic fuse to a trip threshold of 20
amperes (for a 120V module) or 10 amperes (for a 230V
module) and turn on the fans.
2. Start the PFC test file ( Pfcxf.tst ) on the AP workstation. It will
put out a 2 kHz sine wave at 0.1 volt RMS and will switch the
load resistance to 2 ohms. Turn the fixture’s gain control all
the way up.
3. Step the signal level up in 0.1 volt increments and watch the
transformer flux “bubble” signal on the oscilloscope (vertical
scale: 20 or 50 V/div; horizontal scale: 1 or 2 ms/div; ×1 scale).
At each step, adjust VR2 to get a smooth, balanced signal.
See Figure 14. There should be no spurious oscillations or
noise visible.
4. When the audio signal reaches a particular level, the CMP box’s
electronic fuse will trip. Set the audio signal back to 0.1 volt.
5. Reset the trip point to 40 amperes (for a 120V module) or 20
amperes (for a 230V module) and repeat steps 2 and 3. The
electronic fuse should trip at about 2.8 kW of output
(measured on the AP)
, with approximately 1.4 volts input.
6. Reduce the AP’s signal level to 0.1 volt. Reset the electronic
fuse and increase the signal level so that the output is about
2.5 kW. Gently adjust VR2 to null the AC current on DMM #3
to a minimum.
7. Turn the Variac down to zero and set the electronic fuse to 60
amperes.
Procedure
4 of 5: Adjusting 2-ohm limits
1. If this is a brand new module (not a repair), set VR3 to
approximately 4 o’clock. If it is a repair or has otherwise
already been calibrated at some time, leave VR3 alone until
after the first power sweep.
2. Set the Variac to 130 volts (for 120V modules) or 260 volts
(for 230V modules).
3. Run the AP test file (
Pfcpwr2k.tst
) for a 2-ohm power sweep
test at 2 kHz.
4. Watch the power sweep on the AP monitor and see where
the power cutback occurs. The target output power level at
2 kHz is about 4.6 to 4.7 kW for the PL 9.0 or 3.6 to 3.7 kW for
the PL 6.0. If the cutback point is not in the target range,
carefully adjust VR3 and then repeat the power sweep. It may
take more than two or three tries to get the right setting.
CAUTION: During the power sweep, keep a finger on the
reset switch of the CMP box. If anything abnormal happens,
such as power cutback at a low level, or audible noise from
the supply module’s transformers,
immediately flip the reset
switch down and hit F1 on the AP computer keyboard to abort
the sweep test.
If you stopped the test due to transformer noise, go back and
start over at the transformer balancing procedure. If you had
not aborted the power sweep, in a short time you would have
destroyed the MOSFETs.
If you stopped the test for any other abnormality, you must
troubleshoot and repair the supply module before continuing.
5. Load the AP test file
Pfcpwr20.tst
, which will change the
signal frequency to 20 kHz, and repeat step 4. This time, verify
that the power cutback does not occur until approximately 4.5
kW for the PL 9.0 or 3.6 kW for the PL 6.0.
6. After competing the power sweeps, press F1 on the AP
computer keyboard.
Procedure 5 of 5: Thermal test
1. On the AP workstation, load the thermal test file
Pfctherm.tst
. It should select the Pseudo (pink noise)
waveform at 2.7 volts RMS amplitude. Make sure the fixture’s
gain control is turned up full. Load the fixture output with the
2-ohm resistance and shut off the fans.
2. The power supply module should shut down within one
minute. The
PROTECT indicator LED on the front panel will
light.
3. After the module shuts down, turn on the fans and await its
recovery.
Figure 2.22. A well-balanced transformer flux
“bubble.”