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Thread: inverter killed my looper pedal

  1. #1
    Junior Member
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    inverter killed my looper pedal

    I plugged my Digitech JamMan Stereo into an inverter (12v system in campervan) and it worked for about 15 seconds and now it's DEAD!!

    2 questions: What have I done to it?, and, How do I fix it?

    (my mate says it's because it's NOT a PURE sine wave inverter...?)

  2. #2
    Old Timer J M Fahey's Avatar
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    Your JamMan has an external power supply, and inverter might have killed it, so in principle you should try another, same specs.
    But reading the user manual, I see itīs not a full "power supply" but just a mains to 9VAC "Transformer" , a different beast , which might have passed the wrong voltage to the real regulated power supply inside your pedal.

    If you killed that, itīs beyond average user skills range, youīll need a proper Tech.

    Try the brick power supply on its own, measure the output plug to check whether you have 9VAC there or not.
    If not, maybe thatīs all what happened and a new one will work; if you have proper voltage but JamMan shows no signs of life, not a single Led lights, noting, then itīs Tech time.

    Good luck.

    Ps: you might open it and post a picture of the area around the power jack, you *might* have a clip on fuse there, but not too hopeful, lately factories prefer polyswitches and similar protectie measures rather than antiquated glass fuses.
    IF you have a blown fuse, replace it with ***exact*** same type and rating, do not bypass it or use a larger one.
    Juan Manuel Fahey

  3. #3
    Supporting Member
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    Welcome to the forum.

    There's a fair chance your mate may be correct. Depending on the inverter, there's no way of knowing how well-controlled the output is, particularly if it's lightly loaded. There are two aspects to inverter output - the complex non-sinusoidal output waveform in some can cause a transformer to overheat (compared to regular mains), and the output voltage can be higher than the nominal rating. I tried a cheap one experimentally to see if it would power my TV and the results were pretty depressing - I was lucky my TV survived. About 3 seconds was all I needed to find out this was a bad idea.
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  4. #4
    Member PeterPan's Avatar
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    Of course, do as others have suggested, applying 9VAC first from the jamman wall transformer plugged into ordinary 120V house current and see if the transformer is OK. If not, Eureka... thats the easiest thing to replace.

    If not, looking at the Jamman schematic, the 9V AC supply goes through an internal fuse at BD position D10. Maybe you'll get lucky and it will just be blown. If not, the supply circuit derives a negative and a positive voltage, which is filtered and applied to three regulators, a -5V 79L05 at position U3, a +5V LM117DTX-5V at position U8, and what looks like a buck converter/switcher, a ULM2574-S, at bd position U7. delivering 3.3V. I couldn't find any data on that last IC, but you can check for the presence of -5V to GND at pin 3 of U3, and +5V at pin 2 of U8. As for the 3.3V buck converter (I'm supposing based on the inductor), you should be able to see 3.3V across C41. Hopefully if one of these voltages are missing, it will be because the corresponding regulator is friend, and not because something after the supply has toasted and shorted. If it is a supply, at least repair is likely and do-able. Good luck!

    jammanpower.jpg
    J M Fahey likes this.

  5. #5
    Junior Member
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    I see that it`s not reliable staff. I had a problem - no sound. I couldn't find it in troubleshooting, but the pedal was new and I had to solve this trouble.

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