I took a whack at repairing my 1982 Yamaha CE20 FM synthesizer. No joy, I’m afraid. I didn’t spot any obviously bad (fried) components, e.g., leaking electrolytic capacitors. I re-seated two fuses on the main logic (DM) board. Nope.

Well, the next step is to test the output voltage from the three voltage regulators. Fortunately, the regulator leads are exposed and I won’t need to disassemble the DM and symphonic modulator (SA) boards, again.

The CE20 service manual sadly lacks circuit schematics or a concept of operation. A few LEDs light up, but I don’t hear the familiar click of the muting relay. I wish Yamaha had published a schematic or start-up flow-chart. That information would assist signal tracing and diagnosis.

If I can’t find anything easy to fix, I’ll have to give the CE20 a proper burial. 🙂 The Yamaha Reface DX beats the old CE20 in many ways except for the CE20’s aftertouch keyboard, which was a real pleasure to play. Here’s how the CE20 and Reface DX FM implementations stack up:

                         CE20        Reface DX
                     ------------  ------------  
    Keys             49 full size  37 mini keys
    Key response      Vel sense     Vel sense
                      Aftertouch
    Polyphony
        POLY voices       8             8
        MONO voices       1             1
    Patches
        POLY voices       6          32 total
        MONO voices      14
    Ops per voice         2             4
    Effects               1             7
    Display              No            Yes
    Programmable         No            Yes
    MIDI                Nope           Yes
    Pedals           Exp, Sustain    Sustain
    Speakers             No          2 x 3cm
    Battery power        No            Yes

The CE20 voices are preset-only and cannot be reprogrammed. The Reface DX, on the other hand, has a spiffy user interface and 32 patch locations.

Even mentioning MIDI is a bit of a joke (1982!) and USB wasn’t born yet. Aside from the technical challenge, it’s hardly worth the repair. I ain’t gonna spend money on it…

I took pictures of the main DM board and the SA symphonic modulator board. Enjoy! No surface-mount devices inside. The SA board has the muting relay, BTW, in the upper right corner of the picture. Enjoy the view!

Yamaha CE20 main logic (DM) board

Yamaha CE20 symphonic modulator (SA) board

Copyright © 2025 Paul J. Drongowski