Alto SR400A, Service Manual, Page: 14 / 26

TESTING PROCEDURE
- Switch ON the LOW amplifier output to 4
Ω
load resistor and repeat the above booster check
verifying more or less the same ± VCC1 conditions and verify that the signal must be
symmetrical refer to GND, without detectable distortion and oscillation.
Increase the VOLUME pot. until a signal clipping.
Switch OFF the LOW amplifier out. to 4
Ω
load resistor
Par. 5: COMPRESSOR check of LOW amplifier
-Increase the input signal of 10 dB and check the out. signal to remain constant at 45V
peak
and
if the Signal/Comp. led has changed the lighted colour, from GREEN to RED.
Par. 6: PTC function check on Heatsink
- Heat the PTC temperature sensor with a welder heated tip, in touch with its body, to verify this
protection works properly reducing the amplifier out. signal to few volts on time.
P.S. The check must be done with PTC, placed into heat-sink hole and silicon grease on.
Par. 7: Idle current setting of LOW amplifier
- Decrease to zero the signal generator, then, adjust VR1 trimmer to have a 5mV ±0,5mVdc
voltage drop across R13 & R15 (0,22
Ω)
power resistors.
Par. 8: HIGH amplifier check .
- Select a 10KHz frequency with 0dB amplitude on signal generator.
-
Connect CH2 probe tip of scope on HIGH amplifier output.
- Check that the high amplifier power output signal is 26
+
2V
PEAK
(18V
RMS
).
- Switch ON the HIGH amplifier output to 8
Ω
load resistor and increase the VOLUME pot. -
Verify the out. signal is limited to 22V
peak
.
-
Switch OFF the HIGH amplifier output to 8
Ω
load resistor.
Part .9: Burn-in test
1. Connect the pink noise signal from CD player with the line input of speaker module.
2. Connect 4ohm 500W load resistor with the bass output.
3. Connect 8ohm 300W load resistor with the treble output.
4. Put band switch to the position 1, and then turn on the power switch of speaker module.
5. Adjust the pink noise level from CD player until SIGNAL/LIMIT indicators (red, green) sparkle.
6. Put the speaker module vertical and take the burn-in test for 2 hours.
Part .10: Final inspection
1. Check the electronic performance of the tested unit completely.
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