Yamaha CK88 Owner's Manual page 73

Issue
Sounds are distorted.
Sound output is intermittent and stutters.
No effect is applied.
Moving the Pitch Bend Wheel or Modulation
Wheel does not change the sound.
Nothing is shown on the Display (LCD).
A pedal does not work.
Cannot save files to the external USB flash drive.
Communication between the computer and the
CK does not work properly.
MIDI bulk data transmission does not work
properly.
Restoring the Factory Default Settings (Factory Reset)
The Factory Reset function allows you to restore the CK to its initial condition.
NOTICE
When the Factory Reset function is carried out, all the Live Set Sounds you have stored, as well as the settings of MENU screens
and SETTINGS screens will be overwritten with their defaults. It is wise, therefore, to regularly save backups of important settings
on a USB flash drive.
 Carrying out the Factory Reset
To reset all values to the factory defaults, press the [MENU] button  Job  Factory Reset (page 40).
Suspected cause
The Volume of the connected external
audio device is set too high.
The total number of notes has exceeded the
maximum polyphony (128 notes).
Effects are set to OFF.
The depth is turned to the minimum level.
The value is set to "0. "
The [MENU] button  General  Control
Panel  Display  LCD Switch is set to Off.
The pedal type is not correct.
The pedal is not correctly connected.
Receive SW is turned off.
The USB flash drive is write-protected.
The USB flash drive is not formatted
properly.
The Port settings on the computer are not
appropriate.
Use of the wrong terminals (MIDI or USB).
Wrong MIDI device number.
Other information
Solution
Adjust the volume of the connected
external audio device or use the A/D INPUT
[GAIN] knob of the CK. Or, you can also
adjust the volume from the [MENU] button
 General  Audio  USB Audio Volume
(page 38).
Be careful not to exceed the maximum
polyphony.
Set the effects ON with the EFFECT 1 [ON/
OFF] button or the EFFECT 2 [ON/OFF]
button.
Use the [DEPTH] knob to adjust the effect
depth.
Change the value.
Make sure to set the [MENU] button 
General  Control Panel  Display  LCD
Switch to On (page 38).
If the menu items are not visible, adjust the
contrast from the [MENU] button  General
 Control Panel  Display  LCD Contrast
(page 38).
Set from the [MENU] button  General 
Foot Pedal  Pedal 1 or Pedal 2 (page 39).
Make sure that the pedal's plug is fully and
firmly inserted.
From the [SETTINGS] button  Controllers
 Receive SW, select a pedal and set it to ON
(page 31).
Disable the write protection.
Format the USB flash drive again.
Check the port settings on the computer.
Check the settings.
Check the MIDI device number.
CK88 CK61 Owner's Manual
67