Yamaha QY20 – Evil dead

Just received this machine today. The price was low enough to have a crappy drum machine (if repaired).

All voltages were good, the datas were comming out of the various ICs and the leds worked as well. The lcd on the other hand was dead like a dodo. The interesting part of the schematic is the use of a negative voltage to power up the LCD. Negative voltage created with a buck converter, the MAX680CSA which should output -9V or so. The symptoms were quite odd, when power up nothing on the lcd but once you turn if off, it offers the distinctive fading line of graphic lcd (like an old game boy did).

Well, never trust those Buck converters !!


I guess it did his job properly and decided to retire after 15years or so. The MAX680CSA sort of died, and instead of outputting ~9V3 it only gave -4 volts, not enough to animate the screen. I add a power supply to the lcd_contrast pin and voila…it is back from the dead. Now I need to change that bloody ICs and find a proper way to remove it. I’ll investigate more, maybe there’s somthing loading it down (who knows) but it was the faulty puppy.

I also need to change the littium battery inside.


I had a quick play with it while still open, There seem to be a lot of complex stuff for such old machine, I could only listen to the demo song (which was cheesy). The screen reminded me of my lovely (but now disappeared) game boy ! Interesting thing to note, the massive copper shield in it !

On the down side, the MAX680CSA seems to be quite expensive and only available from big dealer (farnell and co) which offers low shipping only above 30euros of purchase…



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2 responses to “Yamaha QY20 – Evil dead

    • hi,
      Thanks for the links.
      I forgot some items on my last farnell order and I need other things as always. It’ll wait a bit until the next order I think.

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