Ecler MPA4-400, Service Manual, Page: 62 / 72

51-0098-0100 EP14-02 Anglès.doc 2 of 4
- Connect a load impedance formed by a 4
Ω
resistor shunted to a 1
µ
5F capacitor, and
apply a 1KHz square waveform input signal. Using an oscilloscope, observe the output
signal, at the flat level areas of the squared waveform, only two or three ringings should
be detected both at positive and negative slope flanges. Increase the input signal level until
the displayed signal starts clipping. Check that, even when clipping, the ringings do not
grow, and no more ringings than before appear either.
- Verify the THERMAL protection circuitry. Short the unit’s thermal probe pins 1 and 2 (see
the component placement sheet), and verify that the relay releases, while the THERMAL
indicator light up, as the output signal is cutted off and the cooling fan increases its speed
until it reaches maximum airflow.
PROTECTIONS
- Signal generator OFF, 1V scale, select a 1KHz output signal and keep the level
potentiometer down to its minimum.
- Connect a 0'5
Ω load impedance.
- Connect the oscilloscope to the module’s output.
- Switch on the generator and turn up slowly the output level potentiometer, while
checking that the output voltage keeps below these limits, as listed below:
FIRST EVALUATION POINT:
15Vpp (240V)
SECOND EVALUATION POINT: 18Vpp (210V)
Note: the signal clipping should appear without any distortion or ringing. Both evaluation
points are obtained by adjusting the variac’s output voltage.
- Repeat this process on all the other channels.
CHECKING INPUT SELECTION SWITCHES.
Initial positioning:
- IN1/IN1+IN2
→ IN1
- IN2/LINK IN1 → LINK IN1
- LP FILTER ON/OFF
→
OFF
- ST/B IN1/B IN1+IN2 → ST
- IN3/LINK1 → LINK IN1
- IN4/LINK2
→
LINK IN2
- HP FILTER ON/OFF → OFF
0dBV 1KHz input signal to IN1
Millivoltmeter/oscilloscope
connected to channel 1 and 2.
XLR CONNECTIONS: PIN 1 - GROUND, PIN 2 - PHASE, PIN 3 - NON PHASE
IN 2
LINK CH 1
LINK CH 2
IN 4
BRIDGE IN 3
BRIDGE
F
IN 3+IN 4
STEREO
BRIDGE
IN 1+IN 2
ON
IN 4
CHANNEL 4
HP FILTER
OFF
ON
OFF
IN 2
BRIDGE IN 1
STEREO
CHANNEL 2
LP FILTER
IN 1
IN 3 LINK CH 1
CHANNEL 3
IN 1
IN 3
IN 1+IN 2
CHANNEL 1