Alto PBM4 SISTEMA, Service Manual

Page: 19 / 35

1. Instruments
(1) AP (Audio precision)
(2) Dual track Oscillograph
(3) DMM
2. Set up
(1) AP output: 0dBu 1KHz SINE(sine wave), load out 600
Ω
Bal-Float.
(2) AP input: Load 100K
Ω
BNC-Unbal. BW: 22Hz~22KHz. Fltr: A-weighting(12017)
3. Visual check
Inspect the appearance of PBM4. Ensure it is ok; the knob of the potentiometer should be no friction.
4. Test function
(1) Test the Phantom power
The power indicator lights up when you switch on PBM4. Set PHANTOM power switch to ON position.
The black pen of DMM connect to the first hole of MIC jack and respectively test CH1~CH4 of MIC
jack with DMM. The red pen of DMM respectively test the second hole and the third hole, the voltage
is 15V±2V. Set the switch to OFF position after finishing testing.
(2) Set PBM4
Turn all knobs to the middle position and turn all LEVEL knobs correspond to CH1~CH4 to the
maximum. Turn off DSP, the MAIN OUT indicator lights up when the AP signal input from LINE IN jack
of each channel; Set the AP output balanced when you test.
(3) Test DF/FX knobs for the output signal(CH1~CH4), MONITOR knobs and MAIN LEVEL
A. Set LEVEL knobs of CH1~CH4 to the maximum.
MAIN OUT: 3dBu(±3dBu), distortion <0.05%. Adjusting LEVEL knob, the output should be
changed accordingly.
MONTOR OUT LEFT: 8dBu(±3dBu), distortion <0.05%. Adjusting MONITOR knob, the output
should be changed accordingly.
FX SEND: 3dBu(±3dBu), distortion <0.003%. Adjusting DSF/FX knob of each channel, the
output should be changed accordingly
TAPE OUT: 3dBu(±3dBu), distortion <0.05%.
B. Set LEVEL knobs of CH1~CH4 to the minimum.
MAIN OUT: About -60dBu, it should be no signal output.
MONTOR OUT LEFT: About –70dBu(±3dBu), it should be no signal output.
FX SEND: About -70dBu(±3dBu), it should be no signal output.
TAPE OUT: About –70dBu(±3dBu), it should be no signal output.
C. Set the LEVEL knobs to the middle position
18