My Yamaha KX88 MIDI Master Keyboard and how we fixed it

My story (skip if you hate waffling)

One day I entered cash converters simply browsing more junk that I didn't need. I then suddenly stumbled upon a large and very nice looking retro Yamaha keyboard. Knowing nothing about it, I did a quick google and found that it had aftertouch and weighted keys. On that basis alone, I decided to purchase it untested at 280 aud. Little did I realise I purchased one of the greatest MIDI master keyboards of all time...

I took it home and to no surprise, it had the classic "Cash Converter's faults" aka, some of the keys didn't work and the computer froze when change when switching modes. It was a struggle to find a schematic (link below), but I did end up finding one on the web, and not really understanding what could be the problem I thought maybe 4 of the IC chips that connected to the keyboard matrix could be the fault. Although I never got around to ordering new ones yet and thankfully I didn't.

Some time passed and I got very lucky and found a second KX88! (that had been dropped, with broken keys and various dents) at a local recycle centre. Luckily the gentleman there was very nice and I purchased it for a donation of 100 aud. We plugged it in, and it worked perfectly. A true testiment to how well Yamaha built their products in the 80s. So now it was time to get the other working

Faults:

  • the top 4 f sharp keys weren't working
  • velocity on one key was louder than the rest
  • computer would freeze when switching between Single, Dual and Split modes

    • Findings:

  • I put the upper keyboard daughterboard from the tip one in my original one and it just worked! So I learnt that it's not the mboard that has the issue, it's actually the keyboard mechanism itself.
  • The computer will freeze if a key is pressed down constantly. It will wait until the key is back in it's resting position before running code. Therefore, if you have corrosion (or simply lack of contact) on one of the silver key mechanisms, your computer will freeze. Make sure they're clean!
  • No connection to keyboard: if you unplug the IDE ribbon cable to the keyboard mechanism from the motherboard, then the computer will completely freeze, making it a bit annoying to troubleshoot because the entire keyboard mechanism (from my understanding) needs to be fully functional before the computer will decide to work. AKA you can't just test a few keys at a time or one keyboard daughter board, they ALL must work.

    • Solution:

    Credit to my Dad who actually figured it out: The keyboard is now fully working, all it took was to reflow the soldier joints on the keyboard "daughter board" (the pcb attatched to the keyboard mechanism. Thankfully a simple easy fix! Also don't forget to replace the computer coincell 2032 battery. Happy playing!

    Download Yamaha KX88 service manual (with schematic)

    Download Yamaha KX88 owners manual

    email: mail@mikkabaksa.com