Gallien-Krueger Backline 100 User manual

Service Manual
Backline 100

Table of Contents
Operating Instructions 3
Turn On / Calibration Procedure
Schematics 9
Engineering Change Orders (ECOs) 1
Bill of Materials 24

Backline100-LeadAmplifier
Turn-OnProcedure
GK Document # 420-0093-C
Board #’s: 206-0093-C (pre amp), 206-0094-C (power amp)
Backline100-alloptions12/9/92 Rev.11/23/99-SW
SETUP
1) Variac on zero, power switch off- connect power cord.
2) Connect output to load box with both sides connected together.
3) Resistance loads open (switch in center), speaker on.
4) 1X probe to scope-A.
5) Load box to scope-B and AC-VM.
6) Setoscillatoron 200Hzsine wave@5mVrms (-26dBV).
7) DVMon20mV range.
8) ACvoltmeteron 30V range.
9) Scope-B on10V/cm (or5Vuncalibrated ).
10) Scope sweep on 1ms/cm, scope trigger on B.
11) Connect reverb wires from preamp - red to output of reverb.
12) On Backline Front Panel, set knobs to 0, switches out.
POWERSUPPLYANYPOWERAMPTEST
1) With power switch on, gradually increase variac to 50V. Listen to speaker and watch scope for no current draw.
2) Check preampsupplies- +/-16VDC (+/-1V margin).
3) Adjust variac to 120V and turn speaker off.
4) Set bias. Hook DVM across collectors of Q6 and Q81 and adjust R50 (on ’94 board) for 2mV across power resistors (R11, 24,57,79).
5) Connectoscillator to return(200Hz @ -26dBV). Output= 9Vrms.
6) Increaseoscillatorto –6dBV(500mV).
7) Turn on 8 ohm load. Output = 16Vrms.
8) Turn load to 4 ohms. Output = 9Vrms.
9) Increaseoscillator to+4dBV(500mV). Signal shouldclip at 22Vrms.
10) Turn on 2nd load to 4 ohms. Signal should round off and go to 13.5Vrms.
INPUTSET-UPANDLEADCHANNELTEST
1) Power LED only should be lit.
2) Engage channel switch (S4). Lead LED should turn on.
3) Oscillatorto input (200Hz@ +4dBV). Engage lead2 switch (S2).
4) Look at drain of Q10- adjust R6 so signal clips evenly on both sides- should be 22Vp-p centered 2.5V.
5) AdjustR91(1ktrim) for7.5-8VDC ondrain ofQ86 (J113).
6) AdjustR104(1ktrim) for7.5-8VDC ondrain ofQ96 (J113).
7) Increase gain to 10, watch signal become square wave at Q96- should clip evenly at 10Vp-p.
8) Decreaseoscillator levelto –66dBV(.5mV). Signal =1.6Vrms (AC).
9) Set tones to 10, gain and volume to 12:00, switches out (lead in).
10) Set scope-B to 5V/cm and 1ms/cm.
11) Set oscillator to 200Hz square wave at –66dBV.
12) Look at output, compare to Fig. 1.
13) One at a time, turn tone knobs to 0 and compare to figures (resetting after finishing each): Bass to 0- Fig. 2; Mid to 0- Fig. 3; Treble to 0-
Fig.4.
14) Engage Input Shape (S1), compare to Fig. 5. Disengage.
15) Engage Lead 2 (S2), compare to Fig. 6. Disengage.
16) Engage EQ Shift (S3), compare to Fig. 7. Disengage.
CLEANCHANNEL,PRESENCE,VCV,ANDREVERBTEST
1) Disengage Channel Select switch- change oscillator to –46dBV.
2) Look at output, compare to Fig. 8.
3) One at a time, turn tone knobs to 0 and compare outputs (resetting to 10 when done): Bass to 0- Fig.9; Mid to 0- Fig. 10; Treble to 0- Fig. 11.
4) Presence to 10- Fig. 12. Reset.
5) Engage EQ shift (S5), compare to Fig. 13. Disengage.
6) EngageVCV (S6), compareto Fig. 14. Disengage.

7) Reverb knob to 10- Fig. 15. Reset.
8) Scopeto 50mV/div. Line out (J5) lookslike Fig. 14 (differentscale).
9) Scope to 5V/div. Headphone outs look like Fig. 8.
FOOTSWITCHTEST
1) With a stereo cord, connect RF2 to footswitch jack on front panel.
2) Engage Channel Switch and Lead 2 switch to the front panel.
3) If necessary, push footswitches so both LEDs are off.
4) Compare output to Fig. 8.
5) Engage Channel footswitch, LED on panel & footswitch light. Output goes up.
6) Engage Lead Channel footswitch, footswitch LED lights, output goes up.
NOISETEST
1) Remove oscillator input.
2) Connect speaker to output and listen to noise. It should be clean with no distortion or crackling on both channels.