Electro-Voice Precision Series Service Manual page 10

clipping. The distortion rate of the limited signal is at THD = 1 % ... 2 %. Increasing the input signal up to a
value of +21 dBu should not result in remarkably higher clipping.
5.2.2. LIMITER FAST/SLOW-Test
• tests have to be performed for both channels of the power amplifier individually: testing has to be
performed without load resistors connected.
Drive the power amplifier with a burst signal (f = 1 kHz, 1-10 cycles, rate: ≈ 0.5 sec.) and U(E) =
1.)
+10 dB above the nominal input voltage.
2.) When monitoring the output signal via oscilloscope, continuously press the FAST/SLOW-switch.
• SLOW: after 2-3 signal periods, the limiter controlled the major distortion down to a minor residual
distortion (THD = 1 % ... 2 %).
• FAST: already after 1-2 signal periods, the limiter controlled the major distortion down to a minor
residual distortion (THD = 1 % ... 2 %).
When shipped, the appliance is set to SLOW!
5.3. POWER-ON DELAY:
Approximately 2 seconds after switching the power on, the relays E1 and E3 which are located on the printed
board assembly 86207/86211 and the relay E1 on the printed board assembly 84157 (channel A/B) pull
simultaneously.
5.4. FAN CONTROL:
Upon powering-on the power amplifier, the fans will run for approximately 2 seconds and stop when the power
amplifier has re-gained its "normal" temperature. In idling condition (power-on, no signal present) the fans are
switched between the SLOW and OFF mode, depending on the heat sink's temperature. When the switch S001
on the printed board assembly 86207/86211 is closed, the fans will run with FAST speed. When shipped, the
S001 switch is set to "OPEN"!
Connecting a variable resistor (approx. 50 kΩ) between CNBSERV 5 and CNBSERV 6 allows for testing the
functioning of the fans. During operation, CNASERV 6 can be utilized to monitor the temperature of the heat
sink.
FAN SPEED U(DC)
CNASERV 6
Stufe 0 < 6.5 V
Stufe 1 6.5 V ... 7.5 V
Stufe 2 7.5 V ... 9 V
Stufe 3 9 V ... 12.5 V
Protect > 12.5 V
5.5. SOAR-PROTECTION TEST:
Channels separately driven up to 69.3 V on 4 Ω. Parallel connect a 0.1 Ω resistor. The protection circuit reacts
and tries continuously to re-start! The protect-LED blinks in the same rhythm.
5.6. SHORT-CIRCUIT CURRENT-LIMITING TEST
testing has to be performed for both channels of the power amplifier individually:
- drive the channel with a burst signal (f = 1 kHz, 1-10 cycles, rate ≈ 1 sec.) without load, with U(A) = 89 V
- connect a load resistor of 1 Ω.
- the short-circuit current-limiter limits the output voltage at the load resistor symmetrically (monitor via
oscilloscope!) to a peak voltage value of 45 V ( approx. 45 A).
5.7. DC-VOLTAGE-PROTECTION TEST
• HI/LO-Cut off, Limiter set to SLOW
testing has to be performed for both channels of the power amplifier individually:
- drive the power amplifier with a test signal (f = 7 Hz) and without load resistor connected.
- at an input voltage of approx. 3 Vpeak the protection circuit reacts and tries continuously to re-start!
The protect-LED blinks with the same frequency.
- Repeat the test with f = 14 Hz; the power amplifier should not switch off.
5.8. HF-PROTECTION TEST
Caution: it is mandatory to drive the power amplifier without load resistors connected. Set the fan service
switch to ON and the HI/LO-Cut to OFF. Switch off the limiter via S102 or by disconnecting the bridge between
CNASERV 1 and CNASERV 3. Drive the power amplifier with a with 7 Vrms and a sine burst of f = 60 kHz
All manuals and user guides at all-guides.com
U(DC)
CNBSERV 4
0 V
12.5 V
19.5 V
27.5 V
27.5 V
5
Remarks
Fans are not running
Power amplifier is switched off