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Yamaha EL70 problems

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  • Yamaha EL70 problems

    Thank you for allowing me on your forum, it must be one of a kind.

    My granddaughter came in a week or so ago and switched the organ which resulted in a loud 100hz hum typical of smoothing capacitor failure. Once I found how to get it apart I removed the main amp board and found that the capacitors had been leaking and had damaged the print on the underside, I replaced the capacitors and repaired the print and to my amazement it worked! Or at least it did at first, it went off, just the audio then came on again when I tried it later, it is now silent.

    The output from the voltage regulators was about right but they seemed to be getting very hot, I don't know how hot they are supposed to run never having had it apart before. The situation now is the everything seems to work, I can feel the three relays coming in, all the buttons work, you hear the disc drive and the tempo section is responding to the appropriate instructions but no sound.

    I have felt all the IC's but none seem to be running hot and have tapped and wiggled everything else but no success. I wonder if anyone can help me. I am not a very good organist but I was a TV engineer for 50 years so no a bit about electronics.



  • #2
    Have you:
    Checked the master volume control?
    Tried headphones?
    Tried putting a signal into the AUX input?
    Listened for a signal at the AUX output?



    • #3
      Tucson dave has some good suggestions. Also make sure that the other power supply components are ok, there’s no AC ripple and the diodes in the rectifiers are all running as expected. If the voltages are ok, the transformer should be ok, but take a look at it to be sure. Voltage regulators shouldn’t run hot as far as I know. Once you’re sure the power supply is ok, you can troubleshoot the downstream components. Tucson Dave’s suggestions will help you find out if the amplifier is ok or not. If not, you may want to replace the capacitors there if you haven’t already.

      Current: Allen 225 RTC, W. Bell reed organ, Lowrey TGS, Singer upright grand
      Former: Yamaha E3R


      • Larason2
        f Forte
        Larason2 commented
        Editing a comment
        Voltage regulators burning up also makes me think of a short somewhere. I would check over your green wiring work and make sure there’s no short there.

    • #4
      Did you change all the caps on the board. I've had a couple of students fix their EL90 by changing the major caps but then had problems until they changed all the other e-caps.

      Also, one had issues with the circuit traces near the connectors. A bit of reflowing the solder joints soon sorted that.

      Might be something different, but worth checking out.
      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


      • #5
        Thank you for all your comments, sorry for delay, I thought I might get an email so didn't look here.

        I have established that I have a signal on headphones which pleased me immensely, but not on the speakers. There appears to be a relay that connects the speakers on the output side of the phones circuit. I suspected the relay might be faulty so obtained a substitute one from Germany - still doesn't work but the new relay has a transparent cover and I can see that it is not being actuated. I have tested the relay on an external 12v supply and it works, even though it is 24v, I also tested the one I took out which seems to be OK.

        There is no coil voltage on the relay and the circuit doesn't help much in seeing where it comes from, I have blown it up so that I can actually see it but it only shows the signal input and output wires, none for the coil. I think if the switching voltage was present it would work.

        I did change all nine of the large electrolytics

        Any suggestions?


        ppp Pianississmo
        Last edited by PeterN; 01-14-2022, 04:19 PM. Reason: Spelling


        • #6
          Given the relay and tone generation is working ok, it could be an amplifier problem. It depends on the relay design whether they actuate to interrupt the signal or actuate to permit the signal. I would try feeding the output to the amplifier into a known working amplifier if you have one. If you’re getting an appropriate signal, it’s an amplifier problem. If not, it could be the relays or some other problem between tone generation and the output signal. I suspect it’s an amplifier problem, in which case the amplifier will need to be rebuilt.

          But also don’t forget your burning up voltage regulators!

          Current: Allen 225 RTC, W. Bell reed organ, Lowrey TGS, Singer upright grand
          Former: Yamaha E3R


          • #7
            On the EL70 overall circuit diagram 4/4 locate the PU schematic.
            At the lower right corner is the speaker protection circuit. This drives the relay coils.
            It protects the speakers from any DC voltage that might come from a defective amplifier module.
            Check for DC at the left end (schematic view) of resistors R213, 215, 216, and 218. Any DC indicates a faulty amplifier.
            If one is bad then replace both amplifiers.



            • #8
              Thanks for all your comments, have fixed it now. I replaced the speaker relay - which didn't make any difference due to the fact that there was no 24v on the coil, the replacement one had a clear plastic cover so I could see if it was closing, it wasn't.

              When the original failure occurred there had been a burn up under the panel and some print had been damaged, when I dug the carbon out it went halfway through the panel in one place, anyway I repaired it or replaced with wire, I had another look at it yesterday with a bright light and magnifier and found a very thin section of print had gone o/c although it looked OK, I replaced it with wire and lo and behold I could then see the relay closing and there was sound.

              Thanks again for all your help, I was hoping not to get involved in anything like this again as at 82 I have really had enough but there was a certain amount of satisfaction gained.