Bose 1600VI Service Manual page 33

8. Potentiometer Tracking Test
8.1 Apply a 16 mVrms, 1 kHz signal to both
channels of the amplifier under test.
8.2 With both gain pots on the front panel
fully CW, reference a dB meter to the
output level of one channel.
8.3 On the same channel, turn the gain pot
CCW one notch and note the dB reading.
8.4 Repeat step 8.3 for each of the first
seven notches of the gain pot for the
channel under test.
8.5 Turn the pot fully CW again, and repeat
steps 8.2 to 8.5 for the other channel.
8.6 Compare the output levels noted for
both channels for the first seven notches of
the gain pots, and verify that all of the steps
are within 1.5 dB of each other from one
channel to the other.
9. Display Test
9.1 With both gain pots fully CW, apply a
10 mVrms, 1 kHz signal to both channels of
the amplifier under test.
9.2 The bottom-most LEDs on the display
located on the front panel should be
illuminated.
9.3 While observing the LEDs on the front
panel, slowly increase the input level. You
should see each one of the LEDs light up
one at a time from bottom to the top of the
display until the red clipping indicator for
each channel illuminates. Be careful not to
overdrive the amplifier for too long a period.
10. Amplifier PCB Bias Adjustment
Note: The bias level should be set without
an input signal or a load on the outputs.
Refer to the PCB layout diagrams for part
locations.
TEST PROCEDURES
33
10.1 Using a DVM, measure the DC
voltage across one of the emitter resistors.
For the 1600VI amplifier, measure across
R144, R145, R148, R149, R150, R151,
R154 or R155 for channel 1. Measure
across the corresponding emitter resistors
for channel 2. For the 1800VI amplifier,
measure across R144 through R155.
Measure across the corresponding emitter
resistors for channel 2. Refer to the ampli-
fier PCB schematic diagrams located in
this service manual for more information.
10.2 While reading across one of the
emitter resistors, adjust R124 for channel 1,
or R224 for channel 2, until you read a
1.5 mVdc voltage drop across the resistor.
Note: To ensure that the emitter resistors
share the bias current equally, it is recom-
mended that you measure two or three of
the emitter resistors for that channel. Equal
bias current sharing is indicated by a
1.5 mVdc voltage drop across each emitter
resistor.
11. 1800VI Amplifier High-Voltage Rail
Adjustment
Note: The rail voltages should be set with
the AC line input voltage at its nominal
value and with no input signal or output
load. Refer to the layout diagrams for part
locations. The rail voltage for the 1600VI
amplifier is not adjustable.
11.1 Use a DVM to measure the DC level
across TP1 to TP3 located on the power
supply PCB.
11.2 Adjust R36 on the regulator PCB until
you read -106 Vdc ± 2 Vdc.
11.3 The reading across TP1 and TP2 on
the power supply PCB should be approxi-
mately +104 Vdc.