Gallien-Krueger 200MB, 200RCB Service Manual

Service Manual

200MB

Table of Contents

Operating Instructions 3
Turn On / Calibration Procedure 6
Schematics 9
Engineering Change Orders (ECOs) 18
Bill of Materials 19

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 outK) 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 50-60V rms.
Regulated supplies = -14.3V (+or-) .5V/ 14.2V (+or-) .5V.

6) Adjust variac to 120V rms 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) V olume 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 =20V rms.

14) Current limiter test. Change to a 2 ohm load. Output should be a clean sine wave without clipping
and = 12Vrms (+or-) .5V rms.

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 = 550mV rms (1.5Vp-p).

18) Check balance out left ( J8) and right (J9). Both should = 5.5V rms 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 = 3.4V rms / Ring = 3.4V rms or 13Vp-p clipped.

21) Test return.
A) Plug input into return (6). (400Hz 50mV rms sine) –26.0 dB. Output = 4Vrms.
B) Line out (J10)= 80mV rms.

22) Change to square signal at input (400Hz –26.0dB).

23) Test tones and filters and compare figures.

24) Chorus test.

Note: Trigger is on the channel, the scope probe is on, and connect to D.0 (J5) @ 1V/div . This will make it
possible to make measurements without having trigger problems. An external trigger could also be used.

A) Volume at 9 o’clock
B ) Master at 10.
C) Tones on 5.
D) Engage chorus.
E ) Rate 0/ Depth 0. Deviation = 1.3 sec. / Rate = 1.5 sec.
F) Rate 0/ Depth 10. Deviation = 5.0 sec.
G) Rate 10/ Depth 10. Rate = .25 sec.
H) Disengage chorus.

25) Balance out test. Sine input (400Hz 50mVrms) –26.0dB.
A) V olume on 5.
B ) Master on 10.
C) Tones on 5. Balance out left pins 2 and 3 and balance out right pins should look different. Left

should swell up and down to a min. and max. value. Right should do the same, however

oscillate right and left.
D) Engage chorus.
E ) Stereo switch out.
F) Push in stereo switch (mono mode). Signal on left and right should look similar, swelling up and

down.
G) Chorus off.

26) Check speaker cut-off switch.

27) Disconnect input.

28) Proceed with noise and tap test.
A) Controls on 10, switch out = noise <60mV rms.
B ) Controls on 10, contour in = noise <80mV rms.
C) Controls on 10, comp. in, sustain 0 = noise < 50mVrms.
D) Controls on 10, comp. in, sustain 10 = noise< 250mV rms.
E ) Controls on 10, comp. in, sustain 10 = noise< 300mVrms.
F) Contour in, chorus in = noise< 40mVrms.
G) Contour in, master on 0= noise< 2.5mVrms.

Noise should be clean without popping or cracking.