SERVICE MANUAL
Contents
1. KORG MS 20 CIRCUIT DIAGRAM 2 KLM 128 KLM E KORG MS 20 4 FRONT VIEW OF PRINTED CIRCUIT BOARD KLM 127 KBD FOLLOWER POWER SUPPLY Q s Ome 8 KORG MS 20 FRONT VIEW OF PRINTED CIRCUIT BOARD KLM 128C KLM 128C 322 D 910 5518 renee ExT Sia in pi ta KORG MS 20 5 PARTS LIST Mechanical parts not listed CARBON RESISTORS POLYSTYRENE CAPACITORS ROTARY VARIABLE not listed 50 3000 x 1 RESISTORS 50 62007 x 1 10KB x 4 METAL FILM RESISTORS 100 x 8 1 4W1 1000 x 2 e POLYPROPPYLENE 100KA x 4 1 4W 1 4032 x 18 CAPACITORS AMB x 2 1 4W 1 4270 x 22 200V 022 F 1 2 6 x 3 IMA x 2 1 4W 1 2 x 3 TRANSISTORS Printed 10 1 1 AW 1 2 949 1 28 564 5 4 Printed 10KB 1 1AW 19 4 27 0 1 2SC 945 L K 1 Printed 1MB x 1 1 40 1 OQ x 1 special selected Printed 4 ganged 100 1 1 4W 1 15 x 1 2SC 1583G x 2 24 10KB x 1 1 20K2 x 2 28 16858 13 Center click stop 10KB x 1 1 4W 1 619kQ x 17 2SC 644R x 1 1 4W 1 100k 23 ROTARY SWITCH 1 AW 1 11040 x 1 SRM 1034 1 150 4 1 44 1 5 11 x 1 25 3000 4 2SK 30 GR 4 SOLID RESISTORS ESK 431 37 key 1 4W 10 10MQ x 7 DIODES 18 1855 x 33 TERMINAL LUG BOARD MYLAR CAPACITORS 24 x 1 not listed LED GD4 203RD x 4 PU2. tese Manca MS 20 CONTENTS 1 SPECIFICATIONS 2 STRUCTURAL DIAGRAM 3 CIRCUIT DIAGRAM 1 CIRCUIT DIAGRAM 2 FRONT VIEW OF PRINTED CIRCUIT BOARD KLM 1280 5 PARTS LIST Mechanical pars not ste 8 BLOCK DIAGRAM 7 ADJUSTMENT PROCEDURE KEIO ELECTRONIC LABORATORY CORPORATION TOKYO JAPAN KORG Ms 20 1 SPECIFICATIONS lt CONTROL SECTION gt 1 Keyboard 2 Voltage controlled oscillator 1 3 2 4 V C O master control 5 mixer 6 Voltage controlled high pass fiter 7 Voltage controlled pass filter 8 Envelope generator 1 9 Envelope generator 2 10 Modulation generator 11 Manual controller 12 P Switch and volume 13 Indicator C C 37 keys octaves Scale 32 16 8 4 6 octaves cent cent Wave form A N PW TU white noise 4 modes Pulse width adjust 1 1 1 Scale 16 8 4 2 6 octaves cent cent Wave form N rL N ring modulator 4 modes Pitch 1 OCTAVES Master tune 100 cent Portamento max 00 sec Frequency modulation intensity by MG T EXT 45V Frequency modulation intensity by EG1 EXT 5V V C 0 1 level C O 2 level frequency 50Hz 15 000Hz Peak fiat self OSC frequency modulation in tensity by MG TEXT 75V 5V Cutoff frequency modulation in tensity by EG2 EXT 5V 459 Cutott frequency 50Hz 15 000Hz P
3. Exemal LP filer frequency control input 2OCTA 5 45V VCF external modulation input T ex 5 45V External initial gain control input 0 5v EG 1 envelope signal normal output 5V vz0V EG 1 envelope signal reverse output 45V OV 1 EG 2 wigger input oo SEG 1 trigger input oo EG 2 envelope signal reverse output A 4 OV MG Triangle output IS A SVp p t 0V Rectangle output I um ance Noisegenerator Pink noise output SVp p 20 White noise output SVp p 20 Sample and hold Clock trigger input Sample signal input 5Vp p max S H output 5Vp p max Modulation Control voltage input 0 5V Signal input 5V 5 Signal output 5V 5V Manual controller Control wheel output 5V OV 5 Momentary switch output oo Signal out Signal output 2Vp output in pedance 3 5k0 Head phones Head phones output 80 120m watts 5 6 Power consumption 10 watts Dimensions 569 W x 309 D x 249 H mm Weight 77kgs Accessories Patch cord connection cord 35cmx2 3mx 1 Options Stand hard case foot pedal MS 01 Junction box MS 02 KORG MS 20 2 STRUCTURAL DIAGRAM Rotary knob lar u large Rotary knob small E PC Board 2 iff Y KORG MS 20 3 CIRCUIT DIAGRAM 1 Tovce or VCO 1 STAB
4. the CV high semi fixed screw as necessary so that C 3 produces half the voltage of C 4 b Measure C 2 and then C 1 in the same way Adjust the KBD CV low semi fixed screw as necessary so that C 2 produces exactly half the voltage of C 4 c Repeat steps a and b as many times as necessary until the output voltage of each of C 1 C 2 3 and C 4 is exactly half that of the next eng DIGITAL VOLTMETER QC TEE A Tolo 1 C 2 Fig 7 4 VCF Fc adjustment Connect a frequency counter to the PHONES jack since a high output level is needed for measure ment Set VCO 1 and VCO 2 level a 1 VC HPF Refer to the settings shown in figure 2 Set the LPF PEAK knob at 0 and the HPF PEAK knob at 10 Then adjust semi fixed screw as necessary so that the HPF oscillation frequency is 500Hz 2 VCLPF Set HPF PEAK at 0 and LPF PEAK at 10 Then adjust the semi fixed screw in the same way as you did for the HPF FREQUENCY COUNTER lo 1 Fig 2
5. PROCEDURE 7 1 Power supply check 1 Positive ripple Should be no more than 2mVp p Set oscilloscope vertical gain at 10mV cm and check that power supply ripple is 2mV or less 2 Negative ripple Same as positive should be no more than 2mVp p 7 2 Pitch adjustment 1 VCO 1 Perform adjustment with synthesizer controls at normal setting Scale 8 Wavetorm ru Master Tune Pitch and all other knobs at 0 See figure 1 a Play C 4 high C on the keyboard and ad justthe high semi fixed screw until you obtain the correct tuning as indicated by WT 10A connected to the SIG OUT jack b Play key C 1 and adjust the low semi fixed screw c Repeat steps a and b as many times as necessary until both are tuned to the correct pitch d Check the tuning of C 1 C 2 and 4 on the WT 10A meter to make sure pitch devia tion is within 2 cents for each e Change the scale to 32 16 8 and 4 and check the tuning of all four C keys to make sure that the pitch deviation of each is within 10 cents 2 VCO 2 Set the VCO 1 level at 0 and the VCO 2 level at 10 Then follow the same procedure as for VCO 1 by adjusting the high and low semi fixed screws 7 3 KBD CV adjustment Use a 4 1 2 digital voltmeter to measure the KBD CV OUT signal Measure output voltage first when you play key C 4 then when you play key C 3 The output voltage for C 3 should be exactly half that for 4 Adjust
6. SH SWITCH STYROL CAPACITORS MS 102 x 1 50V 12000pF x 1 PHOTOCOUPLER 73 035 2018 x 1 CONNECTORS CERAMIC CAPACITORS DEAE SOV 56pF x 1 q x 2 50 22 x 1 4558 x 17 SP x 2 50 100 x 5 081 5 Px 4 50V 220pF 2 TL 071 BP x 2 50 47 x 1 3140 3 25 100000 x 2 082 x 1 SP TL 072 Female Connectors TANTALUM CAPACITORS 3140 3P x 10 16 3315 1 14007 x 2 2 16V 6 8uF x 2 140698 x 2 3 04011 1 T x 2 ELECTROLYTIC CAPACITORS amp PC339C 1 8P x 2 16V 10uF x 12 14315 x 1 16V 33uF x 2 15 x 1 16 1007 x 4 KORG35 x 2 50V iF x 6 25VATF x 1 SEMI FIXED RESISTORS 25 10000 x 1 SRI9R 10kB x 6 16V 2204F 1 SRI9R 0 7 KORG MS 20 6 BLOCK DIAGRAM 2 EXT SIG IN 3 MAX 2VPP CV OUT 1 40 84v 9 PORTAMENT MUT KEY o SCALE jvo 56007 neo jm 4 0 gt VCOI 2 EXT CV IN PHONES 5 EGI EXT EG2 EXT O TRIG OLEO coe INITIAL EXT GAIN EG 1 2 53 TRIG INC h MG OWAVE FORM O TAY O o oFREO 5V EG2 NA As o HOLD aa SS ma ATTACK SUSTAIN 9 RELEASE So l E To REV OUT O CONTROL IN PUT CLOCK IN DELAY ATTACK POINT O KuMi28 RELEASE KORG MS 20 7 ADJUSTMENT
7. eak fiat OSC frequency modulation in tensity by MG TEXT 78V 459 frequency modulation in tensity by EG2 EXT 5 45V Delay ime 10 sec Attack time 10 sec Release time 10 sec Hold time 20 sec Attack time 10 sec Decay time 10 sec Sustain level 0 5V Release time 10 sec Wavelom IN A 2 N Frequency 1 1 1 80 9 wheel center click 0 1 2 20H2 Momentary switch eo Volume LED trigger MG rate EXTERNAL SIGNAL PROCESSOR gt 1 Control section 2 Inputand output 3 Indicator LED Inputsignal level 088 max cut frequency 50 2 500 2 High cut frequency 100 5 000H2 CV adjust Threshold level SSignal In auto pad system 1 0 14 0V Amplitier Out Band pass fitered Out CV Out F V 0 8 4V ENV Out 0 5V Trig Out 5V oro Peak indicator Trigger indicator PATCH PANEL gt 2 10 12 13 14 15 16 18 Keyboard Keyboard control voltage output exponential O 8 Keyboard trigger output 5V Xoo VCO 1 VCO 2 control voltage input linear response 0 8v VCO 2 control voltage input linear response 0 8V vco VCO 1 VCO 2 extemal frequency control input OCTA 45V 5V vcr Extemal signal input HP cutoff frequency control input 20 5 5
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