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Old CryBaby wah pedal nnot "wah-ing"

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  • Helmholtz
    replied
    A few ohms high on a multiple switch series circuit can be all that it takes to bring the sense circuit to a halt.
    Right, but I didn't mean checking contact quality but identifying switched contact pairs of an unknown switch or relais.

    BTW, my DMMs beep and read resistance at same time and my old analog meter changes sound when it doesn't see a perfect short and doesn't beep above 10R.

    As always: Know your meter(s).
    Last edited by Helmholtz; 10-15-2020, 10:16 PM.

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  • Jazz P Bass
    replied
    When checking multiple wiring connections it may be useful to hear the continuity 'beep'.
    Personally, I want to know what the resistance reading is.
    A case in point. A few ohms high on a multiple switch series circuit can be all that it takes to bring the sense circuit to a halt.

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  • Helmholtz
    replied
    Originally posted by g1 View Post
    Continuity is something I think is probably intended for wiring, like automotive or household electrical. You either have a continuous wire (some low ohms) or open connection..
    Checking continuity is useful when you expect a low resistance but don't need to know the exact value. E.g.: Tube heaters, low voltage bulbs, shorts and opens, switches, intermittent contacts/shorts etc.
    It is especially useful for tracing circuits (finding connected components/circuit points).

    To avoid misinterpretation the meter's resistance limit for "continuity" should be known.
    Last edited by Helmholtz; 10-15-2020, 08:18 PM.

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  • Fred G.
    replied
    I totally see your point. I was thinking about this last night, I mean, logically, if there's a connection, there should be "continuity", but I can see that it can be a very arbitrary consideration. You should, logically, see "continuity" across both sides of a given resistor, but as you said...at any rate, thank you for the discussion, and for your help!

    Fred G.

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  • g1
    replied
    Originally posted by Fred G. View Post
    I get a continuity reading between the pins of the coil, I'm assuming this means the coil is good? But if there were an internal short inside the coil, I'd get continuity also, correct?
    Glad to hear you got it fixed. If your meter does have a continuity setting, then yes, a shorted coil and a good coil would both give a 'go' reading for continuity.

    But to clarify what I said earlier about 'continuity', it doesn't really mean a lot unless we say exactly what we mean by it.
    Some meters have a continuity beeper. It may beep at anything less than 200 ohms. Other meters will only give the continuity beep if the reading is less than 40 ohms. I would argue that a 100K resistor that measures near 100K has 'continuity'. So it really is kind of nebulous and it is much preferred to stick with 'resistance' and actual ohms readings.
    Continuity is something I think is probably intended for wiring, like automotive or household electrical. You either have a continuous wire (some low ohms) or open connection..



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  • Fred G.
    replied
    Well, it's good to know I can come here with questions and get a great supportive response! Thanks everyone, I appreciate your help!

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  • vintagekiki
    replied
    Congratulations.
    Persistence is always rewarded in the end.

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  • Fred G.
    replied
    FIXED!!! I wired a flying lead from the terminal of the inductor where the board trace had lifted and broken. Voila, wah wah!

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  • Helmholtz
    replied
    Originally posted by Fred G. View Post
    I get a continuity reading between the pins of the coil, I'm assuming this means the coil is good? But if there were an internal short inside the coil, I'd get continuity also, correct?

    I'm not going to rewind the coil, I'll just put in a new one if need be.
    What resistance do measure between coil pins with coil out of circuit?

    AFAIK there is no direct replacement coil regarding appearance and pin spacing. While a generic 500mH inductor will work, a replacement coil would considerably lower the value of the pedal and might change the sound.

    Rewinding is easy and invisible and won't change the sound if well done..

    I'm sure a rewound or open original '68 halo inductor has some collectors' value (though I would not spend more than 50€ if I needed one ).
    Last edited by Helmholtz; 10-14-2020, 08:16 PM.

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  • Fred G.
    replied
    I get a continuity reading between the pins of the coil, I'm assuming this means the coil is good? But if there were an internal short inside the coil, I'd get continuity also, correct?

    I'm not going to rewind the coil, I'll just put in a new one if need be.

    On closer examination last night (desoldering both joints to the board) I found a completely broken section of the trace, I'll repair this with a flying lead

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  • Helmholtz
    replied
    This "Halo" inductor is a P18/11 type pot core without airgap.
    Similar types I built from kits required between 500 and 700 turns. These are just ballpark numbers depending on actual ferrite type.

    If rewinding is required, it is essential to count the original turns. Without knowing the exact turns number you will need an L(CR) meter to determine the AL- value of the core. AL- value is inductance per number of turns squared.

    Inductance of my original '68 halo measures 630mH. Variance between originals can be assumed to be at least 20%.

    When (re)assembling the core make sure that the faces between the core halves are perfectly clean. Even a tiny dust particle will cause an unwanted airgap and drop inductance significantly.

    If the wire broke at one of the pins a repair without rewinding should be possible.
    Last edited by Helmholtz; 10-14-2020, 05:04 PM.

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  • Mick Bailey
    replied
    This type of inductor is clipped together and can be separated to get to the bobbin. If it does appear to be beyond repair then it can be rewound - I've done a few of this type, though by way of experiment rather than repair. I'm in agreement that the most likely break (if any) would be where the external leads/pins connect and careful observation under magnification may show up where the break is. Inductors though are a pretty reliable component so make sure that it really does read open.

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  • The Dude
    replied
    ^^^^^^That. I'll add: Often, the coil wire breaks right where it solders into the circuit board and the coil itself is salvageable by adding a piece of lead from the break to the board. I'd remove it and inspect it for breaks.

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  • g1
    replied
    Originally posted by Fred G. View Post
    I'm reading continuity across the inductor, but - wouldn't this indicate that the coil is OK?
    Originally posted by Fred G. View Post
    Wouldn't a good inductor give a positive continuity reading, though (a beep)?
    Once again, the term 'continuity' is problematic. Did you or did you not measure continuity at the coil? Never mind, that's a rhetorical question.
    You are not getting the proper resistance reading across the coil.

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  • vintagekiki
    replied
    Originally posted by vintagekiki View Post
    If you measure a 33k resistor and instead of a small resistance you get a value of the order of 30k, there is a high probability that something is wrong with the 0.5H coil.
    Careful on the pins of the 0.5H coil check the resistance.
    The resistance of the coil is measured at the pins of the coil (A, B)
    Click image for larger version  Name:	51854.jpg Views:	0 Size:	253.8 KB ID:	915727
    Please photo PCB side after the intervention.

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