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  • 860 issues

    My 860 was working, sound, fast, slow, stationary, but would completely shut down after about five minutes. If I waited about 20 minutes and started it again it would do the same thing. One time I had left it on and it died completely. Inspecting the fuses revealed that the 1/16 amp slow-blo fuse was blown. I replaced it and it had sound as it should but as soon as I hit the slow speed button on the Combo Preamp III the horn moved maybe half an inch and the same fuse blew again. This time the sound from the speakers kept going but I cannot get rotation of the horn or drum. I know my way around a schematic, and can relate a schematic to the actual circuitry. I can replace parts. Could use some help from you experts. Thanks.
    Last edited by gapo3; 04-11-2020, 04:00 PM.

  • #2
    Hello,

    I think there is something abnormally hot somewhere.
    After a few minutes of heating place your finger on the transformer, the motors and on the power transistors.
    You should be able to maintain it on a few seconds without burn.

    Disconnect the circuits 1 by 1.
    - The loudspeakers (when plugging in and unplugging with power ON you should not ear a loud a Honk)
    - Motors.

    Retry tests.

    Confined JP

    If you are bored of changing the fuses, install a 100W incandescent lamp instead of the fuse.
    A bright light indicates that a problem is still present.

    Comment


    • #3
      This is a good time to reinforce the lesson that 99.5% of the time, fuses do not blow for no reason. "Maybe it's just a fuse" is a running joke among professional techs.

      That fuse is in the AC mains supply to a small transformer T2 that is always powered whenever the 860 is plugged in, 24-7. It supplies the control current used to turn on the power relay REL1 that turns on power to the main power transformer T1. It also provides the control current for the motor switching circuit. If the fuse blew, it would suggest a short somewhere in that circuit -- or a shorted C1 capacitor. However, capacitor shorts are not common in these. The diodes on the motor control board are sometimes known to short, so that might be one thing to test, especially D11.

      You should not be getting any sound from the speakers if the 1/16A fuse blows. That should shut everything off. If you are still getting sound with it blown, something very strange is going on -- or REL1 is stuck in the ON position.
      I'm David. 'Dave' is someone else's name.

      Comment


      • #4

        I got some new 1/16 amp fuses and soldered one in. While exploring I also found some poor soldering where pins on a connector were loose, having lost any connection. I resoldered any spot on the main board that looked questionable and turned her on. I had sound but as soon as I hit the slow speed button to start rotation the horn moved about an inch, blew the 1/16 amp fuse, and lost sound. I thought ok, let's just take it to an expert so I called what looked to be a reputable place in LA and he told me not to bring it in, just that the fuse was too small and I should put in a 1 amp fuse. He followed that with a comment that he does not often work on solid state stuff. Now I am less confident in that shop. I know enough to repair old single channel guitar tube amps if I have a schematic but make no claim to higher expertise in electronics. Further help is greatly appreciated. Looks like I may just have to go in with my limited knowledge on this thing and start testing parts. Any chance it might be that first relay (REL 1) on the board next to the T2 transformer?

        Comment


        • #5
          In Los Angeles, places I know are Ken Rich Sound Services and Advanced Musical Electronics. Was it one of those places you called?

          Looking at the schematic, chances are more likely that it's Relay 3 or D15. D15 is a flyback diode for the Relay 3 coil.

          What is happening is that when you engage Slow, too much current is being drawn through the control circuit. There are a limited number of things that could cause that.

          Do you know how to check a diode with a multimeter to see if it's shorted?
          I'm David. 'Dave' is someone else's name.

          Comment


          • #6
            Originally posted by gapo3 View Post
            ... I called what looked to be a reputable place in LA and he told me not to bring it in, just that the fuse was too small and I should put in a 1 amp fuse. He followed that with a comment that he does not often work on solid state stuff. Now I am less confident in that shop.
            Following this advice will probably end in something burning up, and could ruin one or more transformers, for a start.
            Last edited by muckelroy; 06-25-2020, 02:37 PM.

            Comment


            • #7
              I would run from that guy! I have a rescued 720 from a church that was hit by lightning. Someone had installed a *30* amp fuse prior. One of the amp modules caught fire, soon igniting the wood of the cabinet. If someone hadn’t been there to see it, the building might have become involved. Needless to say, don’t oversize fuses 8)
              Tom in Tulsa

              Fooling with: 1969 E100, 1955 M3, 1963 M100, Leslie 720

              Comment


              • #8
                I have a collection of 20 Amp fuses I've removed from amps. Lots of idiots out there.

                It's especially bad since, in an 11-pin Leslie, that control voltage power supply is powered on 24/7, whenever the Leslie is plugged into a live outlet, regardless of whether main power is turned on or not. It could catch fire while you think it's turned off if not fused properly.
                I'm David. 'Dave' is someone else's name.

                Comment


                • #9
                  I actually got two 720s from that church, the other was also over-fused. On that one, one of the diodes across a reed relay coil shorted and destroyed the little control transformer. No actual flames but it was fried "crispy".
                  Tom in Tulsa

                  Fooling with: 1969 E100, 1955 M3, 1963 M100, Leslie 720

                  Comment


                  • #10
                    It was neither Ken Rich Sound Services and Advanced Musical Electronics that I called. I live in the central valley of California so nothing is real close.
                    I checked diodes 2 and 3, and 10 and 11, and 13 through 16 with the diode/continuity testing selection on my little multimeter and all tested ok, connection one way and not the other. I broke the lead off of one of the tiny glass diodes (d11) when trying to reinstall one of the leads. What is the part number for this diode? I live more than an hour away from the closest Fry's so it will be a while before I get a replacement even if I order it on the Internet. Thanks all for the help directed to me thus far.

                    Comment


                    • #11
                      D11 is on the fast motor. 1N4148 will do the same.
                      But you can replace D11 with what you have in your drawers such as 1N4007 that can be found everywhere in electronic devices.

                      If the fault is on the slow motor and the diodes are good then the relay must now be measured. Correct value is ~ 1000 ohms
                      (TWH RELAY-SS Reed Relay for Solid State Leslie Models)

                      These relays are wound with a very thin wire and they sometimes burn. Then value is ~ 0 Ohms.

                      JP
                      Click image for larger version  Name:	860_Control.jpg Views:	0 Size:	55.1 KB ID:	734104

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                      • #12
                        Relay DCR is marked on the schematic as 500 Ohms, not 1000.

                        Like JP says, you can use any diode equal to or with higher ratings than the original. Since diodes are so cheap, it's a good idea to keep some in stock.

                        Since you said you talked to a tech in LA, I assumed you were closer.
                        I'm David. 'Dave' is someone else's name.

                        Comment


                        • #13
                          If the amp was on "stop" on the pre-amp pedal the 860 worked but as soon as I hit slow or fast it would blow the 1/16 amp fuse. I checked relay 2 and relay 3 and they both checked out at 500 ohms (+- 2%). So those seem fine, though they look like they have been hot. Again, diodes 2 and 3, and 10 and 11, and 13 through 16 checked out fine with the diode/continuity testing selection on my little multimeter, continuity one way and not the other. And again, I broke the lead off of one of the tiny glass diodes (d11) when trying to reinstall one of the leads. I do have some 1N4001 diodes, which I assume would be a satisfactory replacement for d11 (or d10, d15, d16 for that matter). True? Still, I have not yet discovered the reason for the fuse blowing. Continuing thanks for your continuing suggestions and help.

                          Comment


                          • #14
                            Hello,

                            > 1N 4001 = Perfect replacement for all the diodes of this circuit.
                            > If the relays and the diodes are ok, may be the problem is elsewhere.
                            > If you are bored of blowing fuse replace it by a bulb 40-60W 130V~ incandescent. In case of short, the bulb will lit brightly that indicate the problem is still there.

                            JP

                            Comment


                            • #15
                              I tried it out with a the light bulb replacing the fuse. Hitting slow it lit dimily until turned off. Hitting fast it lit brightly. When fast turned off (and slow already off) it went from bright to dim and then off. How should I proceed? Any chance something going on in my Preamp III that may be causing the problem?
                              Last edited by gapo3; 07-08-2020, 05:21 PM.

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