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Repair Information for Yamaha Electones with Dead Channels or No Sound

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  • Repair Information for Yamaha Electones with Dead Channels or No Sound

    I have a tip that may be helpful for many Electone failures. It is likely applicable to most of the EL series and possibly other digital Electones.

    I picked up a nearly dead EL-900 for free several months ago. Reverb, sustain, lead voices, pedal voices, rhythm, and percussion were all dead. Only Voices 1 and 2 were working. I knew from repairing another Electone that the first thing to check is the main power board, which also carries the audio amplifiers. Bad capacitors often cause failure on these boards. By feeding audio signals into the AUX IN and RHYTHM IN inputs, I was able to verify that both channels of the audio amplifier were working properly, and there was no reason to suspect the power supply board as all voltages were correct. Next I connected the MIDI outputs of the EL900 to my laptop and ran Garage Band, and was able to verify that both manuals and the pedals were sending MIDI data (and somewhat unique to the EL-900, also sending horizontal touch); in other words, the entire organ was functioning perfectly as a MIDI controller. These diagnostic findings suggested that the problem was somewhere between the digital MIDI control section and the production of analog signals prior to the audio amplifiers.

    I found online hints that the DAC’s (digital to analog converters) in some Yamaha keyboards (both pianos and organs) are prone to failure, often leading to the complete loss of sound output, or to the loss of one stereo channel. The EL-900 (and I suspect many other EL series organs and Yamaha keyboards) uses the Burr-Brown PCM1702U DAC chip, a 20 bit DAC in a 20 pin surface mount IC package. The EL-900 has 8 of these on the main processing board (called the DM board in the EL-900). The EL-900 service manual (which I obtained from Taro for a mere $US10—thanks Taro!) contains full schematics. The DAC’s are labeled somewhat cryptically, but the labels suggested that rhythm and reverb at least had their own dedicated DAC’s. It seemed at least possible that my problem was bad DAC’s. So I ordered 8 new DAC’s (easily obtainable from eBay and other sources, though they are now discontinued).

    For the EL-900, it was necessary to remove the upper manual in order to access the DM board, and then to remove all of the daughter PC cards that plug into the DM board, the shielding box around the DM board, and an amazing number of connectors that run to the DM board. To make a long story short, once the DM board was physically removed, locating the DAC’s (they are on the underside of the board) was easy. A few hours of careful work with a soldering iron had the DAC’s installed. I now have a fully functional EL-900!

    Let me offer some tips to those of you who may suspect that failed DAC’s are the problem in your Electone or other Yamaha keyboard, and who have some basic knowledge of electronics.

    (1)Get a service manual! It is well worth the cost.

    (2)Do as much diagnosis of the problem as you can before disassembling the organ.

    (3)Test the audio amplifiers and MIDI section of your Electone as noted above. If both of these check out OK, there is a good chance that your problem is bad DAC’s.

    (4)To test the amplifiers, you can connect an iPod or similar audio signal source to the various audio inputs for the test. If you can get sound out of both left and right speakers then the problem is probably not in your audio amplifiers. If you don't get sound from one or both, your problem may be in the audio amps themselves (as I found in another dead organ) or in the power supply (and most of you already know that bad capacitors in the power supply board are a very common cause of failure in Electones).

    (5)To test the digital and controller functions, connect the MIDI outputs to a suitable MIDI device (Garage Band, another MIDI keyboard, etc.) and test whether you can play MIDI through that device. If you can, that suggests that the problem in your Electone is not in the MIDI section.

    (6)If your diagnosis indicates the possibility of bad DAC’s, check the schematic for type of DAC and see whether the DAC’s in your Electone are still available. (My guess is that they all use the same PCM1702U, but you’ll have to verify that.) Consider the number of DAC’s present and the cost of replacements before proceeding.

    (7)If you decide to attempt this repair, be aware that you could go from a partially functional Electone to a fully dead one. For me, the risk was worth the benefit, but it may not be for you. Proceed at your own risk!

    (8)If you decide to proceed, you’ll need to remove the DM board (or whatever board contains the DAC’s) from the organ. Take your time, take a lot of photos as you disassemble the organ, and keep all screws etc. in labeled plastic bags. You’ll be amazed at how quickly you will forget which screw goes where when it is time to reassemble.

    (9)You’ll need a good soldering pen with a fine tip, some SolderWick or similar, proper liquid rosin flux, rosin core solder, and good magnifying glasses. A clean workspace with lots of light is a must.

    (10) To remove the surface mount DAC’s I recommend simply clipping the leads with a fine-tipped pair of diagonal cutters. I tried desoldering them, but the DAC’s are tiny, and it’s too much trouble. Once you clip all of the pins you can lift the chip off and use SolderWick and your iron to remove remaining bits of the pins and carefully clean the pads on the circuit board. NOTE! Do this one DAC at a time. The remaining DAC’s will show you the proper orientation (see below).

    (11) Put a drop of flux on two diagonally opposite pads on the circuit board.

    (12) Lay the new DAC in place, being careful to line pin 1 up in the right place (i.e. don’t make the mistake of installing the chip upside down). Gently solder two opposite diagonal pins in place. This will hold the chip so that you can solder the rest of the pins. Before doing so, flux all pins. Be careful of solder bridges between pins-it is easy to make bridges because the pins are tiny and the spacing is tight. You can remove these easily if they occur with SolderWick. You’ll need an eye-loupe or magnifying glasses for this work—the DAC’s are really, really tiny, but with care, the job isn’t difficult.

    (13) In my case, I replaced two DAC’s only at first, even though I knew I probably needed to replace 6. I reinstalled the DM and its daughter boards and tested the organ. Sure enough, now some of the dead sections were working! I decided to replace all 8 DAC’s since I had the organ disassembled, and because of the possibility of the remaining original DAC’s failing. You may want to replace all of the DAC’s, as they are not terribly expensive.

    (14) The most important thing is to work slowly, to think before every step, and not to be in a rush to finish.

    I hope that this information will be useful to others on the forum. Andy, if you feel it’s appropriate, please feel free to move or duplicate this post in the organ repair section. I may upload some photos later when time allows.

  • #2
    Hi, Just wanted to say thanks for such helpful and detailed information. It is really kind of you to write out every step like this.

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    • #3
      Great! If you'd like to add a similar step by step explanation of the work you did on the e-caps on the power supply board, I'll create a new 'sticky' thread from the results, as these issues are becoming quite common in EL models.
      It's not what you play. It's not how you play. It's the fact that you're playing that counts.

      New website now live - www.andrew-gilbert.com

      Current instruments: Roland Atelier AT900 Platinum Edition, Yamaha PSR-S970, Kawai K1m
      Retired Organs: Lots! Kawai SR6 x 2, Hammond L122, T402, T500 x 2, X5. Conn Martinique and 652. Gulbransen 2102 Pacemaker. Kimball Temptation.
      Retired Leslies, 147, 145 x 2, 760 x 2, 710, 415 x 2.
      Retired synths: Korg 700, Roland SH1000, Jen Superstringer, Kawai S100F, Kawai S100P, Kawai K1

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      • #4
        That's an excellent idea. It may take me a week or two to get around to it!
        Last edited by andyg; 08-22-2018, 12:39 AM.

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        • #5
          No hurry, I'll keep an eye out for it.
          It's not what you play. It's not how you play. It's the fact that you're playing that counts.

          New website now live - www.andrew-gilbert.com

          Current instruments: Roland Atelier AT900 Platinum Edition, Yamaha PSR-S970, Kawai K1m
          Retired Organs: Lots! Kawai SR6 x 2, Hammond L122, T402, T500 x 2, X5. Conn Martinique and 652. Gulbransen 2102 Pacemaker. Kimball Temptation.
          Retired Leslies, 147, 145 x 2, 760 x 2, 710, 415 x 2.
          Retired synths: Korg 700, Roland SH1000, Jen Superstringer, Kawai S100F, Kawai S100P, Kawai K1

          Comment

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