Alto PBM 8.250, Service Manual, Page: 22 / 51

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6. TEST PROCEDURE
PCB test procedure.
1. Assemble the unit according to the sample, turn the power switch on the panel to ON,
when there is no signal between CH1 (J1-11) and CH2(J2-11), these three LED indictors
(D2, D1-16, D2-16) light up. Then D1-4 and D2-4 are lunar,
use the multimeter to check
the voltages on R1-11, R2-11(+15V),R2-12, R1-12(-15V).
2. Bias adjust : no signal input , adjust R1-16(CH1), R2-16(CH2) to make sure the voltage of
R1-17/R2-17is 125±2mV(PBM8.250)/ 130±2mV(PBM8.500);
3. Follow the second step, input a signal at 1KHz, -6dB, the output voltage should be
26±0.5V(PBM8.250)/ 37V±0.5V(PBM8.250), at this time ,distortion factor should be less
than 1%, use the multimeter to test these two terminals of J3, at the beginning, the voltage
of J3 is about 12V, then use a heat gun to blow R3, the voltage will go up to about 26V.
Over-heating protection will be active when use a tweezer to make R1-38(CH1)/R2-
38(CH2) short-circuit. (no signal output)
4. LED indicators on amp circuit board
The middle green LED (D2) lights up, indicating the PCB power is turned on.
LED D1-16, LED D2-16 (green) light up, indicating respectively CH1 and CH2 are at
operating status
.
LED D1-18 and LED D2-18(yellow) light up, indicating the limiter function is normal.
LED D1-21 and LED D2-21(red) light up,
indicating the clip function is normal.
5.
Set the limiter switch at ON position, (J1-6,J2-6 in short circuit ), when input a signal
at 1KHz /+10dB, LEDs
(D1-18 and D2-18
)for LIMITER on the panel will be
illuminated
(bright yellow), and no clip caused on the output signal
6. When the output is MAX., LEDs for limiter on the panel will light up, in protection,
the assumed power is less than 150W(PBM8.500/PBM8.250)
7. S/N rato is more than 90dB( A weighted is more than 100dB)
8. Test compressor function: turn the limiter switch to ON(J1-6, J 2-6 in short circuit),
when input a signal at 1KHz / +10dB, LEDs for limiter on the panel will light up
(bright yellow), and no clip caused on the output signal
9. Adjust VR output voltage to 2V(4 Ω
),verify frequency response that is much better than
25Hz-20KHz+/-1dB.(CH1/CH2)
10.
Press BRIDGE switch, input a signal at 1KHz to CH1( turn the volume of CH2 to MIN.),
connect a 8
Ω
load to the output terminal, verify bridge full load output voltage is more
than 50V(PBM8.250/ 70V PBM 8.500), the distortion rate is less than 1%.
11.
Remove the input signal, then the consumed power is less than 50W