Gallien-Krueger MB150S Service Manual page 12

MB150E Preamp Turn-On Procedure
GK Document #: 420-0087-A / Preamp Board # 206-0087-B
SETUP
1) Power switch off - connect power cord.
2) Connect "power" 3-pin connector from power amp to connector P1 on MB-E board. The colors should read (bottom-top): black, violet,
and brown. (P1 is closest to front of panel.)
3) Connect "signal" 3-pin connector from power amp to connector P2 on MB-E board. These colors should read (bottom-top): white, black
and red. (P2 is furthest from front of panel). Colors should be clearly marked on board.
4) Connect either output to load box (Load A).
5) Resistance loads open (switch in center).
6) Load box to scope-B and AC-VM.
7) Set scope switch on load box to look at Load-A (down).
8) Probe (1:1) to scope-A and DVM. (No GND lead required.)
9) Connect oscillator to input.
10) Set oscillator on 100Hz sine wave @ 0.5Vrms.
11) DVM on 20V (AC) range.
12) AC voltmeter on 30V range.
13) Scope-A on 5V/cm, scope-B on 10V/cm.
14) Scope sweep on 1ms/cm, scope trigger on A.
15) Output level to 0,, switches out.
16) Contour, hi-boost, boost to 0.
17) Volume, tones, and limiter to 10.
POWER AND LIMITER TEST
1) Turn on power switch.
2) Disengage switches on RF2 so that LED's are off. Only the power LED should be lit.
3) Look at output- should be clean sine wave w/ no crossover distortion, and be about 0.6Vp-p.
4) For Combo units: switch on internal speaker and make sure it's connected. Turn off.
5) Change scope to 10V/cm scale.
6) Increase oscillator output to 160mVrms (-16dBV). Output = 21Vrms.
7) Engage limiter. Output falls to 14Vrms.
8) Decrease limiter level to 0. Output falls to 8.5Vrms.
9) Increase output level to 10. Output goes to 11.5Vrms.
10) Disengage limiter. Output should hit rails hard.
11) Switch both loads to 4 ohms- signal should clip on top and bottom, and then shut off after a few seconds. (May have to add 8.2 ohms
resistance.)
12) Remove loads (switches to center) and set output levels to 12 o'clock.
13) Turn unit off and then on again. Note how long it takes before output appears on scope- should be no more than 2-3 seconds.
INPUT SET-UP AND SYSTEM GAIN TEST
1) Turn on power switch- power LED only should light.
2) Look at U1-1 with probe. Adjust R13 (1K trim pot) so signal hits the rails evenly on both side. Signal should be about 22Vp-p.
3) Engage –10dB switch. U1-1 becomes 1.7Vrms. Disengage –10dB switch.
4) Scope trigger to B. Set oscillator to –46dBV (5mVrms).
5) Output level to 10. Output should be about 8Vrms.
6) Engage limiter. Limiter LED should light. (Output raises slightly.)
7) Decrease limiter to 0. Output drops to 6Vrms.
Model #'s: MB150E- All options
Rev. 7/27/99