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A guy on Reddit suggested that the problem is caused by a faulty diode, this seems to be true since the total number of keys affected is 1 + 7 = 8 (a matrix). Any idea what type of diodes is used in these keyboards?

Hello there. So I've got a Casio CTK-5000 Portable Keyboard, and I noticed that when the Eb key on the 4th octave is pressed down, D; C; C#; B; Bb; A; Ab (on the 4th octave also) always play at the highest velocity (= 127) no matter how soft I press them, Even though I can't reach that velocity when pressing any key alone even if I wanted to (Max. = 100). What's wrong with that Eb Key? How do I prevent the mentioned keys from sounding really loud when the Eb Key is pressed down?