Settings / Adjustments; Idling Current Adjustment; Floating - Symmetry; Vca - Offset - Electro-Voice CPS 3 Service Manual

4.

Settings / Adjustments

4.1. IDLING CURRENT ADJUSTMENT

Connect the DC-volt meter at the BIAS measuring points (refer to table) and adjust the idling current via the
trim potentiometer (on the printed board assembly 84158). Adjust both channels of the power amplifier A&B.
Setting Measuring point 1
BIAS HOT A
BIAS COLD A
BIAS HOT B
BIAS COLD B
Adjusting the idling current has to be performed at normal room temperature. In case the power amplifier had
previously been operated, it has to be given several hours to cool off.

4.2. FLOATING - SYMMETRY

Immediately after setting the idle current, a symmetry check of the floating voltage has to be performed. The
power amplifier has to be operated in idling condition. DC-volt meters have to be connected between the
measuring points 1 - 2, and 2 - 3. Using the FLOATING-trim potentiometers that are located on the printed
board assembly 86208/86212, the floating voltage is set symmetric to the ground potential. Not the actual
voltage value is relevant but the symmetry of the + floating voltage and the - floating voltage to the ground
potential.
Setting
FLOTING SYMMETRIE A
FLOTING SYMMETRIE B

4.3. VCA - OFFSET:

Rhythmically open and short-circuit the service switch S101 respectively S201 which are located on the printed
board assembly 86208/86212. Use VR101 respectively VR201 to adjust the power amplifier outputs to their
minimum offset (with oscilloscope to minimal peak value or to the audible minimal volume of the interfering
pulse).
Instead of using the service switch, it is also possible to employ the service connector with short-circuited pins
CNASERV 2 and CNASERV 3 for the power amplifier A, or short-circuited pins CNBSERV 2 and CNBSERV
3 for the power amplifier B.
4.4. ADJUSTING THE METER INSTRUMENTS
• level control set all the way to its clockwise position
• f = 1 kHz
Feed the signal to the inputs A or B so that the IN-LED just lights (U(E) approx. -34 dBu). Adjust the OUT-
LED to approximately the same brightness, using the trim potentiometers VR600 respectively VR601 which
are located on the printed board assembly 86208/86212.
4.5. ADJUSTING THE FANS
Close the service switch S001 on the printed board assembly 86208/86212 or insert a bridge between
CNBSERV 5 and CNBSERV 6. Adjust the voltage at CNBSERV 4 to 27.5 V (DC), using the VR700. Switch
the service switch back to normal or detach the bridge.
4.6. GAIN SELECTION:
The power amplifier's input sensitivity can be set using the jumpers J11 ... J13 or J21 ... J23 which are located
on the printed board assembly 86208/86212. The stated values for the input sensitivity or gain are always
referenced to the level control being set to its fully clockwise position.
CHANNEL A
J11
J12
J13
When shipped, the input sensitivity is set to a value of 0 dBu.
Measuring point 2
CNSERV 2 CNSERV 3
CNSERV 5 CNSERV 6
CNSERV 2 CNSERV 3
CNSERV 5 CNSERV 6
Measuring Measuring
point 1 point 2
CNSERV 8 CNSERV 7
AMP-A
CNSERV 8 CNSERV 7
AMP-B
CHANNEL B
U (DC)
10 mV
10 mV
10 mV
10 mV
Measuring
point 3
CNSERV 9
AMP-A AMP-A
CNSERV 9
AMP-B AMP-B
J21
J22
J23
4
BIAS trimmer
VR1
VR2
VR1
VR2
U(DC) Trim
potentiometer
ca. ± 56V
VR102
ca. ± 56V
VR202
SELECTION
Input Sensitivity 0 dBu
Input Sensitivity +6 dBu
Gain +26 dB