Tone Controls Test; Voicing Filters Test; Noise Test - Gallien-Krueger MB150S Service Manual

INPUT SET-UP AND SYSTEM GAIN TEST (contd.)
9) Decrease limiter level to 0. Output drops to 12Vrms.
10) Disengage limiter.
11) Look at tip of headphone jack (J4). Output should be about 4.2Vrms at this point.
12) Repeat step 11 looking at ring of headphone jack.

TONE CONTROLS TEST

1) Set all large knobs to center (12 o'clock), switches out, small knobs to 0.
2) Set scope-B to 2V/cm and 2ms/cm
3) Set oscillator to 100Hz square wave at –46dBV.
4) Look at output, compare to Figure 1.
5) One at a time turn tone control knobs and compare outputs ( resetting to center after finishing):
A) Treble to 10- Fig. 2; Treble to 0- Fig. 3
B) Hi-mid to 10- Fig. 4; Hi-mid to 0- Fig. 5
C) Lo-mid to 10- Fig. 6; Lo-mid to 0- Fig. 7
D) Bass to 10: Fig. 8; Bass to 0- Fig. 9

VOICING FILTERS TEST

1) Engage low-cut switch- compare to Fig. 10. Disengage.
2) Increase contour to 10- compare output to Fig. 11. Reset to 0.
3) Increase hi- boost to 10- compare output to Fig. 12. Reset to 0.

NOISE TEST

1) Remove oscillator input.
2) Turn large front panel knobs to 10, small knobs to 0, switches out.
3) Connect speaker to output and listen for noise, sound should be clean, no crackling or distortion.
4) Change AC voltmeter range to 0.1V.
5) Noise should measure less than 60mV.
6) AC voltmeter to 0.3V range.
7) Engage low-cut, hi-boost and contour to 10. Noise < 300 mVrms.
RETURN KNOBS TO ZERO- READY FOR BURN-IN.