Gallien-Krueger Backline 100, Service Manual

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Backline 100- Lead Amplifier
Turn-On Procedure
GK Document # 420-0093-C
Board #’s: 206-0093-C (pre amp), 206-0094-C (power amp)
Backline 100- all options 12/9/92 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) Set oscillator on 200Hz sine wave @5mVrms (-26dBV).
7) DVM on 20mV range.
8) AC voltmeter on 30V range.
9) Scope-B on 10V/cm (or 5V uncalibrated ).
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.
POWER SUPPLY ANY POWER AMP TEST
1) With power switch on, gradually increase variac to 50V. Listen to speaker and watch scope for no current draw.
2) Check preamp supplies- +/- 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) Connect oscillator to return (200Hz @ -26dBV). Output = 9Vrms.
6) Increase oscillator to –6dBV (500mV).
7) Turn on 8 ohm load. Output = 16Vrms.
8) Turn load to 4 ohms. Output = 9Vrms.
9) Increase oscillator to +4dBV (500mV). Signal should clip at 22Vrms.
10) Turn on 2 nd load to 4 ohms. Signal should round off and go to 13.5Vrms.
INPUT SET-UP AND LEAD CHANNEL TEST
1) Power LED only should be lit.
2) Engage channel switch (S4). Lead LED should turn on.
3) Oscillator to input (200Hz @ +4dBV). Engage lead 2 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) Adjust R91 (1k trim) for 7.5-8VDC on drain of Q86 (J113).
6) Adjust R104 (1k trim) for 7.5-8VDC on drain of Q96 (J113).
7) Increase gain to 10, watch signal become square wave at Q96- should clip evenly at 10Vp-p.
8) Decrease oscillator level to –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.
CLEAN CHANNEL, PRESENCE, VCV, AND REVERB TEST
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) Engage VCV (S6), compare to Fig. 14. Disengage.