Repairing a Korg Trident MK2

Part 1 - FIXING

The issue

Three issues actually:

Oxydation: some switches are bouncy and pots are scratchy
One voice is out of tune by a semitone when the synth is left unused for some time, but goes in tune when used more regularly
The synth goes crazy after 10-15 min

Fixes

Fixing the oxydation issue

I decided to replace all the 31 tactile switches. The new ones are B3F-4000 from Omron Electronics, costing 0.26 cents each. On the 4 PCB bearing switches (KLM-01, KLM-381, KLM-403, KLM-404), each tactile switch itself is enclosed in a plastic casing wich helds the button and the LED. Remove the button first, the small felt underneath, then desolder the 6 leads (2 for LED, 4 the switch). Its sometime easier to remove the casing first, then the tactile switch.

I took the opportunity to clean the felts: put then all in a little hermetic box, pour some hot water and soap, close and shake vigorously. Repeat 2-3 times with clear water and dry the felts on paper towel.

To remount the switch assemblies, I found easier to enclose the tactile switch in the plastic casing first, and then seats and solder the whole on the PCB. Make sure not to bend any leg.

I spayed some Deoxit D5 in all pots; there is a small hole underneath the legs.

The voice out of tune

Set the Key Assign Mode switch on position 2, then play a key repeatedly. On KLM-377A, a tiny LED lights up to indicates the voice in use: voice 0 is on top. In my case, the bad voice is 5. So far, I didn't went any further since the other issue arose: the synth went crazy.

My guess is a bad electrolytic capacitor; they tends to heal themselves, which may explain why the voice is in tune when the synth is used regularly.

Here is the Korg Trident MK2 Service Manual

The synth goes crazy

Obviously, the heat plays a major role on this issue. And obviously, this issue is related to the CPU.

There are actually 2 CPU in this synth: one on KLM-380A (scanning the front pannel and managing memories), one on KLM-377A (scanning of keyboard and voice assignation). Both are NEC D8048C.

With my oscilloscope, I first probed the power supply pins: Vcc (pin 40) and Vss (pin 20). Everything was clear.

I then probed the XTAL pins (pin 2 and 3). A clean 6 MHz sinusoid: perfect.

I then probed the /RESET pins (pin 4). Ha ha !!. It was supposed to be a fix 5V, but I clearly see downward spikes; both CPU resets on these spikes. Since I see on both, the issue is common, on the RESET line.

The issue was actually really simple to fix, at least temporarily: the culprit is capacitor C28 on board KLM-380. The capacitor legs were bent, almost laying on the PCB. When I raised the capacitor in its standing position, the issue was gone (i.e. I was able to play for hours without any reset). I suspect there is a slight corrosion of the solders due to the original battery. The solders will probably have to be redone, but corroded solder joins are sometime uneasy to redo (the tin doesn't "stick"), and it works so far, so...

Update

A very strange thing happened today: I turned on my Trident this morning (after using it all evening yesterday) and... no sound. I opened the case and found that none of the LEDs on the KLM-377A were active. I suspected the CPU, as it's in charge of scanning the keyboard. The supply voltages are correct, XTAL (pins 2 and 3) shows a clock, RST (pin 4) is in the high state, and I see a signal on pins 27 to 30. I also saw the 16 outputs of the demultiplexer (IC12) activate, so the keyboard scanning is working. But on pins 21 to 23, pressing the keyboard keys only produced a 200mV signal, insufficient to be in a HIGH state. After scanning different points on the board without understanding the cause, I simply... turned the Trident off and on again and everything returned to normal.

Part 2 - CHECK AND ADJUSTMENT PROCEDURE

Caution: Each unit has been completely adjusted at the factory. Therefore, do not adjust anything other than those variable resistors required for servicing.

Wait at least ten minutes after turing on power before beginning check and adjustment procedures.

Test setting diagrams and variable resistor position diagrams are on separate pages.

Where test setting voltages are listed, they are for measurements taken at the control's center.

Preliminary

Please check the following items before beginning adjustment.

Connectors are firmly connected to the correct positions.
Check KLM-380 battery with DVM and confirm 3.60V~4.10V.
Use DVM to check both terminals of R29 (100 Ohm) on KLM-380 and confirm voltage of SmV or less.
Turn on power and confirm that power indicator (on panel and D1 on KLM-385), bank A, programmer-1, brass-8', and strings-8’ LEDs all light up. Also check for sound of relay operation within 3-seconds.
When the tape enable switch is set to the enable position, confirm that the tape enable LED lights up and the bank and programmer LEDs go out and there is no sound from the keyboard.
Select any program; check the edit function and operation of all switches and knobs.

Equipment

The following equipment is required for servicing.

Digital voltmeter (DVM) 4-1/2 digit
Oscilloscope
Tuner (WT-12, etc.)
Audio amp and speakers, or headphones.
Tape recorder

Shortcuts

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KLM-377 check and adjustment (key assigner)
KLM-380 check and adjustment (programmer)
KLM-385 check and adjustment (power supply)
KLM-379 check and adjustment (signal generator)
KLM-378 check and adjustment (synthesizer)
KLM-382 check and adjustment (output)
KLM-384 check and adjustment (keyboard balance)
KLM-403 (293) check and adjustment (brass section)
KLM-401 (291) check and adjustment (effects)

1. KLM-377 check and adjustment (key assigner).

Assign mode check and adjustment.
1. Switch assign mode switch to 1, then, 2, then back to 1 again to reset the assigner.
2. Check assign mode 1 operation: play one note at a time and confirm that KLM-377 LEDs D7~D14 (voices 0~7) light up in order.
3. Check assign mode 2 operation: play a chord and then release it; confirm that LEDs begin to light up from last note released and that there is no shift to another voice as long as you do not play a chord.
4. Return to assign mode 1 after completion.
KBD SPLIT check and adjustment.
1. Check KBD SPLIT operation for synthe, brass, and strings sections.
  1. ◀ ▷ : sound from all 61 keys.
  2. ◀ : sound from bottom two octaves only (to left of ◂ ▹ mark.).
  3. ▷ : sound from top three octaves only (to right of ◂ ▹ mark.).
2. Confirm that all 8 voices split properly between B2 and C3 without any distortion. Adjust VR1 if necessary.
Release cancel check.
1. Check release and cancel functions for synthe, brass, and strings sections.
  1. Set release to 10 for section being checked; set KBD SPLIT to ▷.
  2. Play any eight keys in the top three octaves and release them at the same time to hear the sound of the release condition.
  3. Play any single key in the bottom two octaves eight times and confirm release for each note.
  4. Set keyboard split to ◀ and reverse check procedure for upper and lower octaves.
2. After completion, return to ◀ ▷ position.
OCT/V CV compensation adjustment.
1. Use tuner to check pitch of any particular section.
2. Play G3 and G#3 and adjust VR2 and total tune to obtain a ±0 cent reading for both.

2. KLM-380 check and adjustment (programmer).

Program Load.
1. Make connections between Trident MKII and tape recorder as shown in fig-1.
  Trident MKII TO TAPE → Tape recorder line in (mic in)
  
  FROM TAPE ← Tape recorder line out (earphone out)
Follow procedure to save program data on tape (to avoid erasing user’s program data.)
1. Set tape enable switch and write enable switch to enable.
2. Switch the output level according to input jack of tape recorder.
3. Turn on the to tape SW and confirm the tape enable led lights up.
4. Confirm the programmer LEDs 1~8 light up in order.
How to verify
1. Rewind the tape of 2, set tape, write enable SWs to enable.
2. Turn on verify switch and play tape.
3. Check to see that the FOUND LED lights up as the first part of the data is found, and that programmer LEDs 1~8 light up in order to confirm each program. Confirm that all LEDs go out when all data is correct.
4. If there is an error, the ERROR/CANCEL LED will light and the programmer LEDs 1~8 will stop at the point of the error. If this occurs, check or adjust the tape recorder’s volume and tone controls.
Loading tape data into programmer.
1. Put supplied factory patch tape in tape recorder.
2. Set tape write and enable switches to enable position.
3. Turn on FROM TAPE switch and confirm that LED lights.
4. Play tape and confirm that the FOUND and LOADING LEDs light, and then the programmer LEDs 1~8 light up in order; when all data is loaded, all LEDs except for TAPE ENABLE should go out.
5. Load user's tape (from item 2 above) according to the procedure in item 4
6. Set tape enable and write enable switches to disable.
7. Select several of the programs and play the keyboard to check program contents.
Reset circuit check.
1. Select program A-1.
2. Turn on (slide down) SW1 switch on KLM-3885 circuit board.
3. Check TP2 (+5V) on KLM-385 with DVM; confirm approximately 4.7V.
4. Turn VR1 on KLM-380 clockwise, stopping at the point where BANK A~D, MANUAL, and PROGRAM 1~8 LEDs all light up. (If any LEDs are on before beginning this procedure, turn VR1 counterclockwise until the LEDs go out.)
5. Turn off (slide up) SW1 on KLM-385 and confirm that only PROGRAM A-1 lights up.
D/A adjustment.
1. Set program mode to MANUAL; set VCA attack to 0 and VCA decay to 0.
2. Switch KLM-380 SW1 to test position.
3. Confirm that only programmer LEDs 2 and 7 light up when you switch TAPE ENABLE to DISABLE, ENABLE, and then back to DISABLE. If other LEDs light, adjust VR3 (shift) and VR2 (width) so that only LEDs 2 and 7 light.
4. Turn VR2 clockwise, stopping at the point where LEDs 1 and 8 light up. The change from LED 2 to 1 and 7 to 8 should occur at the same time. If both LEDs don’t change at the same time, adjust VR3 so that timing will be nearly the same.
5. Shift SW1 to normal position and confirm that LEDs 1 and 8 remain lit.
6. Confirm that the PROGRAMMER A-7 LED lights when TP-RST is connected to ground.

3. KLM-385 check and adjustment (power supply).

Power supply voltage adjustment
1. Ground DVM at TP3 (GND).
2. Use DVM to check TP1 (+15V); adjust VR3 as necessary to obtain +14,95V ~ +15.05V.
3. Check TP2 (+5V) and adjust VR1 to obtain +4,990V ~ +5.010V.
4. Check TP4 (-5V) and adjust VR2 to obtain -4,080V ~ -5.010V.
5. Check TP5 (-15V) end confirm -14.70V ~ -15.03V.

4. KLM-379 check and adjustment (signal generator)

PW/PWM adjustment
1. Select program A-7.
2. Check TP1 with oscilloscope and DVM.
3. Adjust VR2 to obtain DC voltage of +1.1V (±20mV).
4. Select program A-8.
5. Adjust VR1 so that sawtooth wave oscillator cycle is 1OOmsec (±10msec).
6. Turn PWM SPEED control from 10 to 0 and confirm that speed gets gradually slower; cycle should be 3~5sec at 0 setting.
SYNTHE waveform check
1. Set assign mode to 2.
2. Connect oscilloscope (0.2V/div, 1msec/div) to TP003.
  1. Select program A-1 and check the items below.
    - Select voice O depending on last note played; confirm change in cycle corresponding to keyboard position.
    - Switch octave selector to 16’, 8’, and 4’ and confirm corresponding changes in sawtooth wave cycle.
    - Confirm no DC fluctuation when octave is changed.
    - Confirm no abnormality in waveform.
  2. Select program A-2 and check items below.
    - Confirm no excessive DC fluctuation when program is switched from A-1 to A-2 (should be less than waveform amplitude).
    - Confirm change in pulse width when PW/PWM knob is turned; waveform should disappear at around 8~10.
    - Confirm no abnormality in waveform.
  3. Select program A-3 and check the following items.
    - Confirm change in PWM depth when PW/PWM knob is turned (from where there starts to be change to where the waveform disappears).
    - Confirm speed change when PWM speed knob is turned (10Hz to about 0.2Hz).
  4. Select program A-4 and check following items.
    - Change VCO2 octave selector from 16’ to 8’ to 4’ and confirm that sawtooth waveform changes accordingly.
    - Confirm absence of DC fluctuation during octave switching. Confirm that DC fluctuation is not excessive when unit is switched from OFF to 16’ (should be about the same as waveform amplitude).
3. Repeat procedures for TP103~TP001 (voices 1~7).
BRASS waveform check
1. Connect oscilloscope to TP001.
2. Check Brass waveform switches.
  1. Confirm that switches will turn 16’ and 8’ waveforms on and off.
  2. Confirm that 16’ and 8’ waveforms can be mixed.
  3. Confirm that there is no DC fluctuation during switching.
  4. Confirm that there are no abnormalities in the waveforms.
3. Repeat check procedure for TP101~701 (voices 1~7).
Strings waveform check
1. Check TP002 with oscilloscope.
2. Check strings octave (scale) switches and confirm the following items:
  1. 16’, 8’, and 4’ waveforms can be switched on and off.
  2. All three waveforms can be mixed,
  3. There is no DC fluctuation during switching.
  4. There are no abnormalities in the waveforms.
3. Repeat check procedure for TP102~107 (voices 1~7).
4. After completion, return assign mode to 1.
Antilog adjustment
1. Check TP3 with oscilloscope and DVM to confirm DC voltage of -9.9~-10.1V.
2. Make sure that assign mode is at 1, total tune is at center, and SW1 is at normal position.
3. Connect DVM ground ta TP3; connect positive probe to TP4.
4. Adjust antilog.
  1. Play C6 8 times and adjust VR4 to obtain 3.200V (±0.002V).
  2. Play C3 8 times and adjust VR3 to obtain 0.4000V (±0.0004V).
  3. Play C1 8 times and adjust VR5 to obtain 0.1000V (±0.0002V).
  4. Repeat above procedure several times and then confirm following specifications.
    Play each note 8 times.
    - C6: 3.200V ±0.003V
    - C5: 1.600V ±0.005V
    - C4: 0.8000V ±0.005V
    - C3: 0.4000V ±0.0004V
    - C2: 0.2000V ±0.0005V
    - C1: 0.1000V ±0.0002V
VCO1 tuning
1. Select program A-5. SW1 (switch 1) should be at normal and the DVM should not be connected.
2. Use tuner to check synthe section output signal.
3. Perform tuning as follows:
  1. Reset assigner by switching assign mode from 1 to 2 and then back to 1 again.
  2. Play C6 and adjust VR004 (VCO1 high, voice 0) to obtain a 0 cent reading.
  3. Play C6, in order, and adjust VR104~704 for voices 1~7.
  4. Play C1 and adjust VR003 (VCO1 low, voice 0) to obtain a 0 cent reading.
  5. Play C1, in order, and adjust VR103~704 for voices 1~7.
  6. Repeat steps (2) ~ (5) several times and confirm following specifications. Play each key 8 times.
    - C6: O±1 cent
    - C5: O±5 cents. Deviation between voices should be within 5 cents.
    - C4: O±5 cents. Deviation between voices should be within 5 cents.
    - C3: O±5 cents. Deviation between voices should be within 5 cents.
    - C2: O±5 cents. Deviation between voices should be within 5 cents.
    - C1: O±1 cents
VCO2 tuning
1. Select program A-6.
2. Use tuner to check synthe section output signal.
3. Perform tuning as follows.
  1. Switch assign mode from 1 to 2 and then back to 1 again.
  2. Play C6 and adjust VR002 (VCO2 high, voice 0) to obtain a 0 cent reading.
  3. Play C6, in order, and adjust VR102~702 for voices 1~7.
  4. Play C1 and adjust VR001 (VCO2 low, voice 0) to obtain a 0 cent reading.
  5. Play C1, in order, and adjust VR101~701 for voices 1~7.
  6. Repeat steps (2} ~ (5) above and confirm following specifications. Play each key 8 times.
    - C6: O±1 cent
    - C5: O±5 cents. Deviation between voices should be within 5 cents.
    - C4: O±5 cents. Deviation between voices should be within 5 cents.
    - C3: O±5 cents. Deviation between voices should be within 5 cents.
    - C2: O±5 cents. Deviation between voices should be within 5 cents.
    - C1: O±1 cents.
Stretch tuning check
1. Set SW1 to stretch position.
2. Check synthe section output with tuner.
3. Select program A-5.
4. Play C1 8 times and check to see that voices 0~7 pitch is all -10~-15 cents (VCO1).
5. Select program A-6.
6. Play C1 eight times and confirm that pitch of voices 0~7 is all -10~-15 cents (VCO02).
Detune check
1. Select program A-6.
2. Check synthe section output signal with tuner; play C3.
3. Confirm that pitch is C♯ ±20 cents when the detune knob is tumed all the way to the sharp side. Deviation between the eight voices should be within 10 cents. (C3).
4. Confirm that pitch is B±20 cents when the detune knob is turned all the way to the flat side. Deviation between the eight voices should be within 10 cents.
Total tune check
1. Select program A-5.
2. Use tuner to check synthe section output; play C3.
3. Set tuner to C♯ and confirm that pitch is between 0 cent and 50 cents when total tune knob is tumed all the way to the sharp side. Deviation between the eight voices should be within 5 cents. (C3)
4. Set tuner to B and confirm that pitch is between -50 cents and 0 cents when total tune knob is tured all the way to the flat side.

5. KLM-378 check and adjustment (synthesizer)

OFFSET adjustment
1. Connect oscilloscope or DVM ground to TP4. (For these items, touch probe directly to check points.)
2. Select program B-1.
3. Check TP001 offset (with DVM or oscilloscope).
4. Adjust VR002 to obtain 0mV (±2mV).
5. In the same way, adjust VR 102~702 for TP101~701.
VCA adjustment
1. Select program B-2.
2. Use oscilloscope (0.1V/div, 1msec/div) to observe TP3 waveform.
3. Play C3 to select voice 0.
4. Adjust VR004 to obtain sawtooth waveform amplitude of 0.6Vp-p (±5%).
5. In the same way, adjust VR104~704 for voices 1~7.
Resonance adjustment
1. Select program B-3. Check TP3 with oscilloscope.
2. Play C3 to select voice 0.
3. Adjust VR003 to obtain sine wave (VCF oscillation waveform) amplitude of 0.2Vp-p (±20mV).
4. In the same way, adjust VR103~703 for voices 1~7.
5. Oscillation for all voices should begin at a setting between 6.5 and 8.5.
Cutoff frequency adjustment
1. Select program B-4.
2. Check TP3 with oscilloscope, tuner, and frequency counter.
3. Play and single key to select voice 1.
4. Adjust VR001 to obtain an oscillation frequency of 523Hz, C ±10 cents.
5. In the same way, adjust VR101~701. for voices 1~7.
6. After adjustment, select each voice and turn the cutoff knob from 0 to 10, checking to see that:
  1. Frequency is 5~20Hz at 0.
  2. Frequency is 26~33kHz at 10.
  3. Amplitude is 0.2Vp-p or more throughout entire range.
EG intensity adjustment
1. Select program B-5.
2. Check TP3 with oscilloscope and frequency counter.
3. Play any single key.
4. Adjust VR4 to obtain oscillation frequency of 5kHz (±500Hz).
5. Confirm oscillation frequency of 5kHz (±500Hz) for each voice. With cutoff at 10 and EG intensity at -5, confirm 50~250Hz for each voice.
6. Select program B-6.
7. Play any single key and confirm that there are no significant pitch differences between the voices.
8. Select program B-7.
9. Play any single key and confirm that DC click noise is within ±100mV for all voices.
KBD TRACK adjustment
1. Select program B-8.
2. Check TP3 with oscilloscope and tuner.
3. Play middle G3♯.
4. Adjust VR5 to obtain oscillation frequency of 523Hz, (C ±10 cents.)
5. Set assign mode to 2.
6. Alternately play G3♯ and G4♯ and adjust VR3 so that there is a one octave (±20 cents) difference the two oscillation frequencies.
7. Set assign mode to 1.
8. Confirm that you hear a close approximation of a scale when you play the middle octave. Each other individual octave should also sound like a scale.
9. Confirm that changes in oscillation frequency correspond to KBD TRACK settings of Quarter, HALF, FULL, and OVER. Note, however, that QUARTER is 1/3 (±10%) of FULL, and HALF is 2/3 (±10%) of FULL.
Resonance compensation VCA adjustment
1. Select program C-1.
2. Set SW1 to off position.
3. Use oscilloscope (0.2V/div, 1msec/div) to check TP1 waveform.
4. Set assign mode to 2 and play any single key.
5. Adjust VR1 and VR2 so that sawtooth waveform amplitude is 0.6Vp-p when resonance is set to 0, and 1.2Vp-p when resonance is set to 10.
  - VR1; controls slope.
  - VR2: controls overall amplitude.
6. After completion, retum SW1 to normal position.
VCA EG adjustment
1. Select program C-2. Set assign mode to 2.
2. Use oscilloscope (5V/div, 50msec/div) to check TP003.
3. Use last note to select voice 0.
4. Play any single key and adjust VR005 to obtain attack time of 250msec (±10msec).
  On oscilloscope, use normal trigger and adjust trigger level for this procedure.
5. In the same way, adjust VR105~705 for TP103~703.
VCA EG attack check
1. Select program C-3. Set assign mode to 1.
2. Play any single key and measure, for each voice, the time between the end of the slow attack end the disappearance of the sound.
  Confirm 15 to 25 seconds for all voices and that there is no more than 5 seconds difference between voices.
VCA EG decay check
1. Select program C-4.
2. Play any single key and confirm that there is no significant difference in decay times between voices.
VCA EG release check
1. Select program C-5.
2. Play any single key and confirm that there is no significant difference in release times between voices.
VCF EG adjustment
1. Select program C-6. Set assign mode to 2.
2. Use oscilloscope to check TP004.
3. Use last note to select voice 0.
4. Play any single key and adjust VR006 to obtain an attack time of 250msec (±10msec).
5. Repeat procedure using VR106~706 for TP104~704.
VCF EG attack check
1. Select program C-7. Set assign mode to 1.
2. Play any single key and measure, for each voice, the time it takes for the cutoff frequency to rise and disappear. Confirm 15 to 25 seconds for all voices and that there is no more than a 5 second difference between voices.
VCF EG decay check
1. Select program C-8.
2. Play any single key and confirm no significant difference in decay time between voices.
VCF EG release check
1. Select program D-1.
2. Play any single key and confirm no significant difference in selease time between voices.
AUTO DAMP check
1. Select program D-2.
2. Check auto damp operation (VCA).
  1. Confirm that each note is released separately when you play in a staccato style.
  2. Confirm that release is heard on all notes in a chord and that when the next note is played, the previous note’s release disappears.
3. Select program D-3.
4. Check auto damp operation (VCF).
  1. Connect Base of Q3 (C945) to ground.
  2. Perform same check as for VCA, above.
Release switch check
1. Select program D-7.
2. Apply S-1 foot switch signal ( ↴ ) to release trig in jack.
3. Check release switch (damper effect) operation.
  1. Release becomes 0 when plug is inserted in trig in jack.
  2. When foot switch signal is applied, release corresponds to knob setting.
  3. Auto damp effect is applied in this condition. Disconnect foot switch after completion,
EXT FcM check
1. Select program B-4.
2. Apply DC-5~+5 control voltage to EXT FcM CV IN jack.
3. Confirm that oscillator frequency changes from a minimum of 5~20Hz to a maximum of 26~33kHz. Disconnect CV after completion.

6. KLM-382 check and adjustment (output)

Attenuator adjustment
1. Select program D-4.
2. Use oscilloscope to check TP2 on KLM-382 circuit board.
3. Play C3 (any voice is okay).
4. Adjust VR1 to obtain sawtooth waveform amplitude of 1.0Vp-p (±0.05V).
5. Confirm that waveform amplitude of program D-5 is ten times that of D-6.

7. KLM-403 (293) check and adjustment (brass section)

Offset adjustment
1. Set controls as shown in diagram.
2. Connect oscilloscope or DVM ground lead to ground on KLM-403 (Test directly with probe for these items.)
3. Use oscilloscope or DVM to check IC13 number 3 pin.
4. Adjust VR10 to obtain 0mV (±2mV).
VCA adjustment
1. Set controls as shown in diagram.
2. Use oscilloscope (0.1V/div, 1msec/div} to check KLM-382 TP7.
3. Play C3.
4. Adjust VR9 to obtain sawtooth waveform amplitude of 0.6Vp-p (±5%).
5. Play C3, in order, and confirm amplitude of 0.5~0.7Vp-p for voices 0~7. (assign mode 1)
6. Use oscilloscope to check KLM-382 TP3 and confirm that waveform amplitude for all voices is 0.8~1.3Vp-p and that deviation between voices is no more than 0.2V. Note: phase is inverted.
Resonance adjustment
1. Set controls as shown in diagram.
2. Use oscilloscope (0.5V/div, 1msec/div) to check KLM-382 TP7.
3. Play any single key.
4. Adjust VR11 to obtain sine wave (VCF oscillation) amplitude of 3.0Vp-p (±0.15V).
Cutoff adjustment
1. Set controls as shown in diagram.
2. Use oscilloscope (0.5V/div, 20~0.1msec/div) and frequency counter to check KLM-382 TP7.
3. Play any single key.
4. Adjust VR12 to obtain 180~200Hz oscillation frequency when cutoff knob is at 5.
5. Adjust VR8 to obtain 56.0~6,0kHz oscillation frequency when cutoff knob is at 10.
6. After repeating adjustments 4) and 5) above, confirm 2~10Hz oscillation frequency when cutoff knob is at 0.
7. Confirm oscillation waveform amplitude of 0.5Vp-p or more throughout cutoff knob setting range.
EG intensity check
1. Set controls as shown in diagram.
2. Use oscilloscope or frequency counter to check KLM-382 TP7.
3. Confirm oscillation frequency of 7.0~10kHz. Confirm that oscillation frequency changes smoothly when EG intensity knob is turned.
EG check
1. Set controls as shown in diagram.
2. Turn attack knob and confirm change in attack time with 2~5 seconds at maximum setting.
3. Turn decay knob and confirm change in decay time with 4~8 seconds at maximum setting.
4. Turn sustain knob and confirm that sustain level changes from 0 to 10.
5. Turn release knob and confirm change in release time with 10~16 seconds at maximum setting.
Trigger check
1. Set controls as shown in diagram.
2. Play any single key.
3. Confirm that MULTIPLE TRIGGER switch turns multiple trigger effect on and off.
4. Confirm that TRIGGER SELECT switch turns trigger select effect on and off. Confirm that the silence note selector determines the number of voices needed to produce a trigger signal in accordance with the knob setting.
5. Connect S-1 foot switch to EXT TRIG IN jack (↴)
6. Confirm that foot switch triggers sound only when TRIGGER SELECT switch is turned on. Disconnect foot switch after completion.
EXT FcM check
1. Set controls as shown in diagram.
2. Use oscilloscope or frequency counter to check KLM-382 TP7.
3. Apply DC -5~+5V control voltage to EXT FcM CV jack.
4. Confirm 2~20Hz minimum and 16~20kHz maximum VCF oscillation frequency.

8. KLM-384 check and adjustment (keyboard balance)

KBD BALANCE adjustment
1. Set strings section controls as shown in diagram.
2. Use oscilloscope (0.5V/div, 1msec/div) to check TP0 on KLM-384 circuit board.
3. Play C3.
4. Adjust VR002 to obtain sawtooth waveform amplitude of 1.0Vp-p (±0.05V).
5. In the same way, adjust VR102~702 for TP1~TP7. (The above is for VCA adjustment.)
6. Set controls as shown in diagram.
7. Use oscilloscope (0.1V/div, 1msec/div) to check TP0 on KLM-384 circuit board.
8. Play C3.
9. Adjust VR001 to obtain 0.6Vp-p (±0.05V) amplitude for waveform shown in diagram.
10. In the same way, adjust VR101~701 for TP1~TP7. (The above is for VCF adjustment.)

9. KLM-404 (294) check and adjustment (strings section)

Vibrato bias adjustment
1. Set controls as shown in diagram.
2. Apply standard signal generator triangle wave to R105 and R106 connection point.
3. Use oscilloscope to check Q11 emitter.
4. Adjust signal generator output and VR3 to obtain maximum undistorted amplitude in the triangle wave.
Ensemble bias adjustment
1. Set controls as the same setting as that of vibrato bias adjustment.
2. Apply standard signal generator triangle wave to R75 and R76 connection point.
3. Use oscilloscope to check Q2 emitter.
4. Adjust signal generator output and VR3 to obtain maximum undistorted amplitude in the triangle wave.
5. In the same way, adjust VR4 for ENSEMBLE 2, and adjust VR2 for ENSEMBLE 3.
Vibrato LFO check
1. Set controls as shown in diagram.
2. Use oscilloscope to check center of vibrato intensity control.
3. Confirm triangle wave frequency (cycle) of:
  - 2~4Hz (250~500msec) when vibrato speed is at 0.
  - 10~20Hz (60~100msec) when vibrato speed is at 10.
Vibrato delay time check
1. Set controls as shown in diagram.
2. Use oscilloscope to check IC21 number 1 pin.
3. Play any key and confirm that the time it takes for the vibrato waveform to begin is:
  - 2~3msec when delay time is at 0;
  - 0.8~1.2sec when delay time is at 10.
  Also confirm continuous variation from 0 to 10.
Output level adjustment
1. Set controls as shown in diagram.
2. Use oscilloscope (0.1V/div, 1msec/div) to check TP8 on KLM-382 circuit board.
3. Play C3 eight times.
4. Adjust VR5 so that sawtooth waveform amplitude is 0.5~0.7Vp-p for voices 1~7.
Envelope check
1. Set controls as shown in diagram.
2. Use oscilloscope (0.1V/div, 10msec/div) to check TP8 on KLM-382 circuit board.
3. Play any key. (Upper octaves are easier to check)
4. Confirm that the waveform’s rising characteristic is smooth and not stepped. Also confirm that there is no noise when attack is set to between 0 and 2.
5. Confirm that attack time changes when attack knob is turned. It should be 10 seconds or more at maximum setting.
6. Confirm change in release time when knob is tumed; should be 10 seconds or more at maximum setting.
7. Confirm that there is no click noise, amplitude ringing, or other abnormalities when attack is at 0. (This checks compander operation.).
Vibrato waveform check
1. Set controls as shown in diagram.
2. Use oscilloscope (0.2V/div, 0.2msec/div) to check TP8 on KLM-382.
3. Play any key.
4. Turn on vibrato switch and confirm that vibrato is applied to the sawtooth waveform.
5. Confirm that vibrato depth changes when intensity knob is turned.
6. Confirm vibrato frequency change when speed knob is turned.
7. Confirm that there is a change in the time it takes for vibrato to be applied when you turn the delay time knob.
8. Confirm that the vibrato off switch turns the vibrato effect on and off.
Ensemble waveform check
1. Set controls as shown in diagram.
2. Use oscilloscope (0.2V/div, 0.2msec/div) to check TP8 on KLM-382.
3. Play any key.
4. Confirm ensemble effect in sawtooth waveform, as shown in diagram.
5. Confirm that ensemble off switch turns effect on and off.
Bowing adjustment
1. Set controls as shown in the diagram.
2. Use oscilloscope (2V/div, 1msec/div) to check IC20 number 8 pin.
3. Turn VR6 all the way clockwise and adjust VR8 to obtain an oscillation frequency of 1kHz.
4. Adjust VR6 so that there are 3 or 4 peaks in ringing characteristic in the sawtooth waveform (using same check point).
5. Confirm that there is a change in the spacing in the ringing characteristic when the tone knob is adjusted.
6. Set Bowing level to 10, Tone to 10, and turn on BOWING switch, other setting the same as above.
7. Use oscilloscope (0.1V/div, 1msec/div) to check TP8 on KLM-382.
8. Play C3.
9. Adjust VR7 so that the ratio between the level right after a note is played and the regular level is 3:1.
10. Confirm that level ratio decreases when level knob, is turned down, reaching 1.4:1.
11. Confirm that the BOWING switch turns the bowing effect on and off.
Noise reduction check
1. Set controls as shown in the diagram.
2. Use oscilloscope to check TP4 on KLM-382 circuit board.
3. Play C3 and confirm that sawtooth waveform amplitude is 0.8~1.3Vp-p (and difference between voices is within 0.2V).
4. Change scale setting from 8' to 4'.
5. Play C6 and confirm that sawtooth waveform amplitude is 0.3~0.7Vp-p (and difference between voices is within 0.2V).
6. Next, ground the base of Q8 (C945) on the KLM-382 circuit board.
7. With this connection, confirm that in the lower octaves of the keyboard, you get a sound without harmonics (a dull sound), and that there is almost no amplitude in the high range of the keyboard.
Equalizer check
1. Set controls as shown in the diagram.
2. Use oscilloscope (0.1V/div, 1msec/div) to check the STRINGS SEPARATE OUT jack.
3. Play C3.
4. Adjust the equalizer high and low controls and confirm that the waveforms match the settings shown below.

10. KLM-401 (291) check and adjustment (effects)

Modulation check and adjustment
1. Select program A-6.
2. Use oscilloscope to check IC13 number 1 pin.
3. Play any key and adjust VR7 so that it takes 0.5 sec between point key is depressed and waveform begins.
  Confirm single trigger.
4. Use oscilloscope to check IC4 number 1 pin.
5. Adjust VR5 so that waveform amplitude is the same when the joy stick is all the way to the TRIL (rectangle) and all the way to VIBRATO (triangle).
  Be careful to move the joystick straight and not to the pitch bend sides.
6. Leave joystick all the way at the TRIL position and check rectangle wave cycle. Confirm following:
  - With speed at 0: 0.6~0.8sec;
  - With speed at 10: 80~120msec.
7. Check synthe section output with oscilloscope.
8. Set joystick intensity to 10 and play any single key.
9. Confirm the following:
  - Pitch changes by ±1 octave (±20~80 cents) when joystick is moved all the way to the pitch bend sides;
  - TRIL goes up by about a minor third (up to E♭ if C3 is played);
  - VIBRATO effect is in order;
  - Intensity can be varied from 1 to 10;
  - Speed can be varied from 1 to 10.
10. Confirm that delayed vibrato is produced when DELAY VIBRATO is turned on and that joystick VIBRATO and TRIL are no jonger applied.
11. With total tune and detune all the way to the ♯ positions and joystick intensity at 10, play C6 and confirm that oscillation does not stop regardless of joystick position.
Bias adjustment
1. Set controls as shown in diagram.
2. Connect standard signal generator to R67, R68 connection point.
3. Use oscilloscope (0.5V/div, 0.5msec/div) to check IC9 number 1 pin.
4. Adjust VR6 to obtain an undistorted triangle waveform.
Clock adjustment
1. Set controls as shown in the diagram.
2. Use frequency counter to check 1C6 number 3 pin.
3. Adjust VR3 and VR4 so that frequency is 90~110 kHz when the manual knob is at 0, and 0.9~1.1 MHz when the knob is at 10.
  VR3 adjusts center frequency.
  VR4 adjusts range of variation.
MIX LEVEL adjustment
1. Set controls as shown in diagram.
2. Use oscilloscope (0.2V/div, 0.5msec) to check TP-2 on KLM-382 circuit board.
3. Select synthe section program A-2 and apply flanger to the synthe sound.
4. Play C3.
5. Turn MANUAL knob up from the 0 position and stop at around 3~5 where waveform amplitude becomes smallest. Then adjust VR2 to further reduce amplitude to the smallest level possible.
Feedback adjustment
1. Set controls as shown in diagram.
2. Use oscilloscope to check TP2 on KLM-382 circuit board.
3. Apply flanger to synthe section (program A-2).
4. Without playing the keyboard, turn the FEEDBACK knob from 0 up toward 10 and adjust VR1 so that the flanger goes into self-oscillation at 7 and above.
Speed adjustment
1. Use oscilloscope to check IC11 number 1 pin.
2. Confirm triangle wave oscillation frequency of:
  - 8~12Hz (80~125msec cycle) when speed is at 10;
  - 0.05~0.08Hz (12~18sec cycle) when speed is at 0.
Operation check
1. Set controls as shown in diagram.
2. Use oscilloscope (0.1V/div, 1msec/div) to check TP1 on KLM-382 circuit board.
3. Confirm that switches control application of flanging effect to synthe, brass, and strings sections. (Listen and check waveform.)
4. Listen to sound and confirm operation of speed, feedback, manual, and intensity knobs.
Noise reduction check
1. Set controls as shown in diagram.
2. Select program A-5 in synthe section.
3. Use oscilloscope (0.1V/div, 0.1msec/div) to check TP2 on KLM-382 circuit board.
4. Apply flanger to synthe section, play a single key in the upper octave (C5~C6) and adjust the MANUAL knob to obtain maximum amplitude.
5. Turn the synthe section flanger effect on and off and confirm no more than ±20% change in amplitude.
6. Ground base of Q6 (C945) on KLM-382 circuit board.
7. With this connection, confirm that when the synthe section flanger effect is turned on and off, the low range produces a sound without any harmonics and the high range has almost no amplitude.

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