Gallien-Krueger 400RB series Service Manual - page 6
400RB-200W Bass Amp
Turn on Procedure
Board #’s: 206-0047-C (preamp), 206-0041-A ( power amp)
Model# 400RB all options
8-19-91
Setup
1)
Variac on zero, power switch off- connect power cord.
2)
Connect either output to load box ( load A).
3)
Resistance loads open ( switch in center).
4)
Speaker on.
5)
Load box to scope-B and AC-VM.
6)
Set scope switch on load box to look at load A (down).
7)
Set oscillator on 200Hz sine wave @ 5mVrms (-46 dBV).
8)
DVM on 20 mV (DC) range.
9)
AC Voltmeter on 30V range.
10)
Scope-B on 10V/cm.
11)
Scope sweep on 1ms/cm, scope trigger on B on RB Front panel, set:
12)
Tones, master and boost to 10, switches out.
13)
Volume on 0.
Power Supply and Power Amp Test
1)
With power switch on, gradually turn up variac to 50V, while listening to speaker
and watching scope and ammeter. Output should go negative then snap back to 0.
2)
Check regulated supplies: (+ or -)14.5V, + or – 1V.
3)
Adjust variac to 120V and turn speaker off.
4)
Set Bias. Adjust R14( on ’41 board) for 5mV across R26, R27.
5)
Power LED and boost LED should be lit.
6)
Connect oscillator to input. ( 200Hz @ -46 dBV).
7)
Turn on 4 ohm load.
8)
Adjust volume for slight clipping( 2-3 o’clock). Output = 28 Vrms.
9)
Engage - 10dB switch- Output becomes 5.7 Vrms. Disengage switch.
10)
Turn boost to 0. Output becomes 3 Vrms.
11)
Turn master to 0. Output becomes 0V.
12)
Turn load off.
Tones and Filter Test
1)
Set all knobs to center (12 o’clock), switches out.
2)
Set scope-B to 5V/cm and 1ms/cm.
3)
Set oscillator to 200Hz square wave at –46 dBV.
4)
Look at output, compare to figure 1.
5)
One at a time, turn tone control knobs and compare output to figures(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.
6)
Engage low-cut switch, compare to Fig.10. Disengage.
7)
Engage contour switch, compare to Fig.11. Disengage.