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Thread: Slick mag problem

  1. #41

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    Quote Originally Posted by wireweinie View Post
    ...<snip>...For a switch that may be 30 or 40 years old, I'd rather replace with new instead of trying to repair the old.

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    That’s just the conundrum: Trying to return the Cub to original means using a 40+ year old mag switch. Thus, repair is the option. Thus, these problems and my questions.... Appreciate all the advice and ideas, guys.

  2. #42
    wireweinie's Avatar
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    A Bendix replacement switch isn't original enough? If not, find a used switch that passes inspection.

    Web
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  3. #43

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    This is an AAF A7 mag switch. Rarer than hen’s teeth. This one is in very good shape and repeatedly passes continuity checks (by different folks using different meters), has firm and definite indents, etc., etc. So I’m not 100% convinced it’s the mag switch itself. I’m waiting to hear back from an old timer at Slick on the wiring. Spoke with him once when I was ordering new P-leads and he mentioned something “unique” about how to hook them up. That idea was overruled by the local A&P so I want to talk with him (the Slick guy) again to be sure I am clear about his method so we can give that a try.

    if I remember correctly, he said to hook up both P-leads to the mags and only one ground wire to one of the mags and to leave the other one disconnected. Interesting. But after seeing several other planes on the field with only one mag ground wire connected maybe that’s the secret sauce.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  4. #44
    wireweinie's Avatar
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    If the switch passes checks then it's good.

    Don't get wrapped around the axle over p-leads. It's as simple as it gets whether it's Slicks or Bendix. Each p-lead is a shielded, single conductor wire. Center conductor connects to p-lead terminal on mag and 'L' or 'R' tab on switch, as appropriate. Mag end of shielding connects to mag body. Switch end of shielding connects to ground tab on switch. Repeat for opposite p-lead.

    That's all there is to it. No magic an no 'unique' connections due to make or model of magneto or switch.

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  5. #45

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    did someone professionally overhaul your switch and put it back together wrong? go to pierces post number15.https://www.supercub.org/forum/showt...gnition-Switch
    Last edited by tempdoug; 06-28-2020 at 02:54 PM.

  6. #46
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    Checking with an ohmmeter is the same for any mag switch. Open contacts = mag is 'on'.

    'OFF' - continuity between 'Left' and 'ground' and 'Right' and 'ground'.
    'Left' - No continuity between 'Left' and 'ground'. Continuity between 'Right' and 'ground'.
    'Right' - No continuity between 'Right' and 'ground'. Continuity between 'Left' and 'ground'.
    'Both' - No continuity between 'Left' and 'ground' or 'Right' and 'ground'.

    When you do these checks, make sure to wiggle the key or toggle to see if the reading is intermittent.

    Web
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  7. #47

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    Quote Originally Posted by YellowFeverAL View Post
    This is an AAF A7 mag switch. Rarer than hen’s teeth. This one is in very good shape and repeatedly passes continuity checks (by different folks using different meters), has firm and definite indents, etc., etc. So I’m not 100% convinced it’s the mag switch itself. I’m waiting to hear back from an old timer at Slick on the wiring. Spoke with him once when I was ordering new P-leads and he mentioned something “unique” about how to hook them up. That idea was overruled by the local A&P so I want to talk with him (the Slick guy) again to be sure I am clear about his method so we can give that a try.

    if I remember correctly, he said to hook up both P-leads to the mags and only one ground wire to one of the mags and to leave the other one disconnected. Interesting. But after seeing several other planes on the field with only one mag ground wire connected maybe that’s the secret sauce.
    Yep, that is normal, it just provides noise suppression for the radio from the P-leads. You also dont want any capacitors on a P-lead for a slick, only bendix modern mags.

  8. #48

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    Disconnected a ground wire from a mag, wrapped the connector in electrical tape and zip-tied it out of the way. Started (and stopped! by turning off the mag switch) five times yesterday. Still not ready to claim success but it’s looking better, for sure.

    Quote Originally Posted by astjp2 View Post
    Yep, that is normal, it just provides noise suppression for the radio from the P-leads. You also dont want any capacitors on a P-lead for a slick, only bendix modern mags.
    This is very interesting. I’d love to learn more about the “capacitor” thing. If you wouldn’t mind expanding on your post I’d appreciate it. Are you suggesting (going out on an electrical limb here) that how mags are connected through a switch somehow creates a capacitor? Perhaps after the engine runs for a while? I noticed before that I could start and stop it after a minute or so and it’d shut down Ok. Then, after a flight of a half-hour or longer it wouldn’t shut down. Perhaps that gives the “capacitor” time to charge? Or am I imagining all this (I have only vague knowledge of electricity/electronics). Yet, given this project’s history, this is why I am reluctant to declare victory (even after a .4 flight with successful shut-down).

  9. #49
    wireweinie's Avatar
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    Quote Originally Posted by astjp2 View Post
    Yep, that is normal, it just provides noise suppression for the radio from the P-leads.
    This is NOT correct.

    IF the ground tab is connected to airframe ground AND the mags/engine/engine mount are all grounded properly, this may be true. But, as some of us detailed above, the shield is used as part of the p-lead circuit.

    With the center conductor on the p-lead stud and the shield on the mag body The current path is from the p-lead stud, through the switch, and back to the mag through the shield. As stated previously, this provides the shortest path for current and isolates the p-lead circuit from the airframe. There are two reasons for wiring it like this. First is noise suppression. As I've said, having a path for the p-lead circuit to not use the airframe, means that any noise generated from the mags will only be present on the p-lead circuit and not routed through the airframe. This minimizes the chances of that noise being 'heard' by your radios or intercom. Second, is reliability. Using the shielded wire as a p-lead means that the p-lead circuit has a minimum of connections. The current path routes directly from the mag, to the switch, and back to the mag. No riveted seams or bolted joints to pass through.

    If you disconnected a ground wire from the mag and the mag was still controlled by the switch, it only means that the ground tab on the switch has been connected to airframe ground. Do yourself a favor and connect your p-leads correctly.

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  10. #50
    wireweinie's Avatar
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    Also, you stated that you purchased Bogert p-leads. Their instructions direct you to connect center conductor to p-lead/switch and shield to mag body/ground tab.

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    Last edited by wireweinie; 06-29-2020 at 11:36 AM.
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  11. #51

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    Web said it better than I could, also in the slick instructions it says to remove any inline capacitors that are in the P-lead.

  12. #52

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    When my P-leads arrived from Bogert’s there were no directions. Just two sealable bags with the two P-leads in them. Nothing suggested teasing out shielding and affixing it to a ground. This photos below are as close to instructions as I got.

    It was a fellow at Slick that (if I recall correctly) said to attach one ground and not the other.Click image for larger version. 

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  13. #53

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    I see one of your problems. You think the Bogart p-lead "come with the P-lead shielded wire and a ground wire for each mag". It is a single shielded wire. The ground is the shield wire. They attach eye terminals to the end of the shield wire (looks like the blue wire to me) and cover it all up with heat shrink. A few years back I spent about 3 weeks trying to figure it all out, between internet time, books, and phone calls to manufactures. I ended up doing it just like Web advised. Also agree no external capacitor on a slick.
    DENNY

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