Yamaha DX7IIFD FM Synthesizer Repair

Yamaha DX7IIFD FM Synthseizer
Yamaha DX7IIFD FM Synthseizer

Recently I acquired a used Yamaha DX7IIFD here in Japan in excellent shape. I already have FM synthesis covered with a Yamaha DX7, TX816, TX802 and a Yamaha DX7IID, however, I really wanted to the Floppy Drive functionality of the Yamaha DX7II. Plus, I’m very fond of the Yamaha DX7II version for controlling the TX802 and TX816 FM synth modules. Basically the DX7IIFD is bitimbral with which you can layer or split the keyboard. If you want, you can sequence two tracks with just one DX7II which is pretty cool.

I mentioned the word repair in the title of this post because I have found with the DX7II, there are a few issues that I’ve ran across that others seem to be experiencing as well. The most notable is the LCD screen contrast losing it’s clarity and becoming more faint. A common question among DX7II users is about the location of the LCD contrast. Unfortunately there is none. When the LCD contrast goes, I’ve pretty much determined that you have to replace the LCD screen all together or perhaps use a computer editor to see what’s going on inside. Note that for editors I primarily use Midi Quest 10XL which works pretty good for seeing all of the parameters.

There does seem to be a DIY way to modify the DMC-40267 display and control the contrast, but I haven’t taken the plunge to do that yet. I’m actually not real sure how that is even implemented so I need to do a bit more research on the subject. What’s interesting though is that I noticed more people are experiencing problems with their LCD screens. Perhaps we’ve reached the limit for the current LCD screens and now they are starting to crack. The original DX7 mkI already has a solution on Ebay for replacing the LCD screen. I have bought and replaced mine with those nifty blue and green screens which work very well.

Other areas of the Yamaha DX7II that might need repairing are the key contacts and program buttons. Both usually just require disassembling the components and giving them a thorough cleaning. Any garbled messages on the LCD screen usually means the battery needs to be changed and then reset. The floppy drive is problem that can happen if you get the famous drive error. I actually had this error show up quite a bit with my newly acquired DX7IIFD, but found that if I formatted the DD floppy from within the DX7IIFD it stopped the error. If I formatted the floppy in the PC, it would cause the problem. Strange! Usually I just do a sysex transfer for patches, but now that I have a working FD drive, it’s cool to be able to hold another 40 banks. To create custom banks you can simply save the patches you like to a memory cartridge and then either sysex that out to the computer or save to a floppy disk.

The keys on the Yamaha DX7IID/FD to also tend to clack a bit more than the regular DX7mkI. I’ve heard you can add some felt strips inside to dampen the noise a bit. I may do this when I get some spare time. Definitely the keys are better on the earlier DX7 model, but the DX7II’s are not too bad, but a little noisy.

Lately, I’ve been using the Yamaha DX7IIFD midi’d up to a Yamaha TX816 and TX802. It works exceptionally well at controlling these two sound modules. I highly recommend using the DX7II as a controller if you have one the TX modules. For patch changes and editing, it really works great!

The Yamaha DX7IIFD Video Manual by The N Y School of Synthesis


5 thoughts on “Yamaha DX7IIFD FM Synthesizer Repair

  1. Paul Le Secq

    Hello Jim
    I think the DX7 IIFD format the floppy in MSX format, like the TX16W do. I have the same error with my DX7IIFD.

    1. Darius

      To change contrast of LCD display you should change value 10k or 390 ohm of resistance divisor on the pin 3 of CN1 connector on the LCD module (look at schematic). I is possible to adjust right contrast according angle of view to the display. I have done it by mounting variable resistor replaing one of resistors.
      Troubles with floppy disk driver are caused by differents of formatting disk by PC and DX7IIFD. Generally standard of DX7 floppy format is MSDOS but is one different. While formatting PC writes data on bootsector which DX7 does not. When on bootsector are data, DX7 report error.
      Another problem with DX7 FDD is that is 720 kB but at PC is 1,44 MB.
      PC driver uses much higher magnetic field to write data, and if you try overwrite something by DX7 drive, it can’t, because his magnetic field is to weak. Result is that old and new data are mixed an DX7 report errors.

  2. Hi, did you manage to repair the DX7II LCD contrast in between? I’d like to know how it’s done if it’s possible without the need for a replacement lcd.

  3. Amos

    Hi Jim,
    Your blog is resourceful and helpful! Bravo!
    Please I need your help on this:
    I have a DXIIFD, but at the moment it sounds horrible. For every chords and note played, there’s distortion and noise that accompanies the sound. Please, what can be done to rectify this problem? Cheers!

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