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Thread: Problem with EH Holy Grail Plus

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    Problem with EH Holy Grail Plus

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    I'm having some problems with my EH Holy Grail Plus reverb pedal. Sometimes it stops working. While the bypass signal is fine and the LED light is on, it produces no reverb before I unplug the power and replug it. It is brand new. Can some effects earlier in the chain cause it to malfunction? It doesn't seem like a good idea to keep unplugging the power cable.

    Chain: Dunlop Crybaby Wah -> T-Rex Spindoctor preamp/overdrive -> EH Stereo Memory Man w/ Hazarai -> EH Octave Multiplexer -> EH Holy Grail Plus -> Boss RC-30 Loop Station -> Interface (Zoom H4n)

    Any ideas? I'm worried it will break

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    Quote Originally Posted by dainbramage View Post
    Any ideas? I'm worried it will break
    I wouldn't worry that it will break, sound like it's already broken... If it's brand new I wouldn't screw around troubleshooting... exchange it... then troubleshoot... not that they'll been any problem to troubleshoot on a different unit that's not defective...
    It's not just the signal chain... It's the hands that touch it

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    Don’t throw away this great effect , i’m a tech and just had to debug a friends Holy Grail Plus that was acting erratically , the circuitry is sophisticated : analog to digital converter , digital to analog converter , microcontroller and a switching power regulator.

    Poking around I noticed that the 5volts that normally supplies all the digital circuitry and that is regulated down from the 9volt input was down to around 4volts and erratic, this will screw up digital circuitry as the voltage tolerance on 5v is a fairly tight 4.7v to 5.3v , outside of this the operation will be erratic : resets , no effect , no sound , whining, etc .

    Fortunately I tracked down the problem to a surface mount component labeled FB3 next to the 9v power connector , this component looks like a fusible resistor or a varistor designed to limit the inrush current when the power supply is initially plugged in , this part is electrically between the power connector and the 5v regulator , from my observation the resistive value has drifted and not enough voltage gets to the regulator witch in turn does not give the regulator enough range for it to output it’s required 5Volts.

    From all the postings I have seen it seems that there could have been a bad batch of this component and this could account for all these similar complaints.

    The fix is relatively simple , the part can be shorted out although it is probably there to protect the regulator from surges , I have tacked a 4.7 ohm ľ watt resistor in parallel witch leaves 8.6v at the regulator input , enough for it to output a solid 5v but still with a little protection .

    Hope this save some of these great effects . Dan Tech.

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    Hey thanks. It's been almost 2 years since I posted this and strangely I have never had problems with the pedal again.
    When the world slips you a jeffrey, stroke the furry wall.

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    Last edited by Sufi; 05-23-2020 at 08:28.

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    Holiest Grail from Eelectro Harmonix

    Quote Originally Posted by Dan Tech View Post
    Donít throw away this great effect , iím a tech and just had to debug a friends Holy Grail Plus that was acting erratically , the circuitry is sophisticated : analog to digital converter , digital to analog converter , microcontroller and a switching power regulator.

    Poking around I noticed that the 5volts that normally supplies all the digital circuitry and that is regulated down from the 9volt input was down to around 4volts and erratic, this will screw up digital circuitry as the voltage tolerance on 5v is a fairly tight 4.7v to 5.3v , outside of this the operation will be erratic : resets , no effect , no sound , whining, etc .

    Fortunately I tracked down the problem to a surface mount component labeled FB3 next to the 9v power connector , this component looks like a fusible resistor or a varistor designed to limit the inrush current when the power supply is initially plugged in , this part is electrically between the power connector and the 5v regulator , from my observation the resistive value has drifted and not enough voltage gets to the regulator witch in turn does not give the regulator enough range for it to output itís required 5Volts.

    From all the postings I have seen it seems that there could have been a bad batch of this component and this could account for all these similar complaints.

    The fix is relatively simple , the part can be shorted out although it is probably there to protect the regulator from surges , I have tacked a 4.7 ohm ľ watt resistor in parallel witch leaves 8.6v at the regulator input , enough for it to output a solid 5v but still with a little protection .

    Hope this save some of these great effects . Dan Tech.
    Hi there!
    I had the same issues with the Holiest Grail and I believe it had to do with the power as well. They don't produce this pedal anymore, I guess they had some problems with it since they don't seem to like talking about it.

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