Gallien-Krueger 200MB Service Manual - page 6
200MB/RCB T/O Procedure
Rev.B- 3/7/88
1)
Inspect board.
2)
Connect mains.
3)
Observe the following:
A) no load
E) volume on 0 I) chorus depth on 0
B) variac at 0
F) master on 0
J) chorus rate on 0
C) trim pots halfway
G) switches out K) speaker on
D) tones on 5
H) sustain on 0
4)
Gradually adjust variac to 25 Vrms.
U20/P4= -1.5V (+or-)-.5V. U20/P8= 3.2V (+or-) -.5V.
Regulated supplies = -.5 V (+or-) .5V./ 7.1V (+or-) -.5V.
5)
Gradually adjust variac to 70Vrms while listening to the speaker and watching variac (AC amps)
and scope. Output should go –8V then +10V, motor a little and settle at 0 between 50-60Vrms.
Regulated supplies = -14.3V (+or-) .5V/ 14.2V (+or-) .5V.
6)
Adjust variac to 120Vrms and turn speaker off. Supply voltage (+or-)46.5V (+or -).5V.
7)
Set bias. Adjust R207 to get 5mV across R197, R208 ( most pos. of the two), and R223, R224
(the most neg. of the two).
8)
Set the following: master on 10.
9)
Connect sine input (400Hz 50mVrms) –26 dB.
10)
Compressor test.
A) Volume on 10.
B) Sustain on 0. U2/P6= 700mVp-p. U4/P7= 2.3Vp-p.
C) Engage compressor. U4/P7= 1.2Vp-p.
D) Gradually adjust sustain to 10. U4/P7 should increase to 1.7Vp-p.
E) Disengage compressor and continue.
11)
Limiter adjustment. Adjust R174 to get a flat response at U21/P2 (compare fig.)
12)
Set the following: volume on 0; 4 ohm load.
13)
Slowly turn up volume just until limiter LED begins to light. At this point, output should be at full
power =20Vrms.
14)
Current limiter test. Change to a 2 ohm load. Output should be a clean sine wave without clipping
and = 12Vrms (+or-) .5Vrms.
15)
Turn master up and down to check if it works properly.
16)
Set the following: volume and master on 10, no load.
17)
Check direct out (J5) pins 2 and 3 = 550mVrms (1.5Vp-p).
18)
Check balance out left ( J8) and right (J9). Both should = 5.5Vrms in stereo and mono mode at pins
2 and 3.
19)
Check send (J7). 1.7Vp-p, clean sine wave. Probe at R229.
20)
Check headphone jack (J3). Tip = 3.4Vrms / Ring = 3.4Vrms or 13Vp-p clipped.
21)
Test return.
A) Plug input into return (6). (400Hz 50mVrms sine) –26.0 dB. Output = 4Vrms.
B) Line out (J10)= 80mVrms.
22)
Change to square signal at input (400Hz –26.0dB).
23)
Test tones and filters and compare figures.
24)
Chorus test.