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Thread: Digitech Whammy IV Problem

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    Digitech Whammy IV Problem

    I have a Digitech Whammy IV that has an issue. Upon powering, all the lights blink a single time and nothing else. The unit has no response from the selector or the switch. The led for the pedal sweep stays lit. The power supply is correct and the unit does the same thing when attempting a calibration. So parts seem to visibly be faulty. I've read this to be a somewhat common experience, so anybody have any thoughts?

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    I repaired one last year. And if memory serves, it was a burnt regulator. Those older units, like many digital devices of that era, used more current than recent devices do. The heat-sinking on the 3-pin regulators was fairly modest, and it is also easy to imagine the thermal compound coupling the regulator to the heatsink drying out over time, allowing one or more of the regulators to overheat and burnt out. I'm not saying that is necessarily what it is, but based on my own experience, that's a good place to start. Check the state of the thermal compound as well.

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    Earlier this year, I repaired a Diamond Memory Lane pedal for a buddy, and it took several e-mail exchanges with the company's tech support until their tech guy remembered that in one of the earliest runs of the pedal, the distributor they bought their regulators from had sent them a pile of defective regulators, whose heat sink tab was about 1/3 the normal thickness. When they'd power up the pedals to calibrate them, they'd test fine. But because the heatsink was so thin, and the regulator was free-standing without additional heatsinking, it would begin to overheat after about 15 minutes, and drift off-spec, yielding a very annoyingly audible HF whine. Since I imagine they'd set up and calibrate the pedals in less time than that, it took them a while (and probably some customer feedback) to identify the source of the problem.

    Three-pin regulators are wonderful things, but they all demand certain thermal conditions to show their best.

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    So you're thinking start with replacing U1 and U2? I read a guy had success with his by replacing the 2 tantalum caps near the chip...no such luck for mine. Any idea what the replacement part values are for U1 and U2?

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    At the very least, take a reading of the output voltages on those two regulators, to verify that they are, or are not, to spec. Remember, if they aren't providing the right power to the rest of the circuit, why should the rest of the circuit do anything? I realize that one often hears recommendation to replace larger-value electrolytic caps. And while there is an outside chance there might be something amiss with these, this IS a fairly recent product, comparatively speaking, so I'm not expecting anything to have dried out.

    And just so we are clear, you can see in the photo that two of the regulators have heatsinks attached, and one doesn't.

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    So I tested the regulators, and I don't have the slightest idea what the values *should* be if faulty. I got U3: 13.85 & 8.92, U2: 12.67 & 4.965, and U1: 3.295 & 6.93. I tested them a few more times and got nearly the same values. I can't say I understand the reading for U1.

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    Quote Originally Posted by stevenrb718 View Post
    So I tested the regulators, and I don't have the slightest idea what the values *should* be if faulty. I got U3: 13.85 & 8.92, U2: 12.67 & 4.965, and U1: 3.295 & 6.93. I tested them a few more times and got nearly the same values. I can't say I understand the reading for U1.
    A regulator by definition regulated power. say a 15 volt regulator may have anywhere from 18 - 25 volts input and will put out a steady 15v.

    Got a schematic?
    nosaj

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    Sounds like you are getting 9V, 5V, and 3.3V out of the regulators. Those are common numbers for digital stuff so quite possibly correct.
    You will need to compare those to the schematic, or post the part numbers stamped on those regulators.

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    schematicwhammy4.pdf

    Maybe this will help.
    nosaj

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    Supporting Member Jazz P Bass's Avatar
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    It looks to me like U3 is snaggered.

    That should be a -5Vdc output.

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    Quote Originally Posted by Jazz P Bass View Post
    It looks to me like U3 is snaggered.

    That should be a -5Vdc output.
    For 1, 2 and 3 the schematic shows +3.3, +5, and -5 respectively. Looks like the one that should be off is U2 by changing about 12.5 in to about 5 out, a -7.5v if I'm reading that correctly.

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    Quote Originally Posted by stevenrb718 View Post
    For 1, 2 and 3 the schematic shows +3.3, +5, and -5 respectively. Looks like the one that should be off is U2 by changing about 12.5 in to about 5 out, a -7.5v if I'm reading that correctly.
    You said" So I tested the regulators, and I don't have the slightest idea what the values *should* be if faulty. I got U3: 13.85 & 8.92, U2: 12.67 & 4.965, and U1: 3.295 & 6.93. I tested them a few more times and got nearly the same values. I can't say I understand the reading for U1."

    U1 should be +3.3Vdc You have 3.295
    U2 should be +5Vdc You have 4.965
    U3 should be -5Vdc You have 8.92

    i think you should retest and repost please.

    nosaj

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    Quote Originally Posted by nosaj View Post
    You said" So I tested the regulators, and I don't have the slightest idea what the values *should* be if faulty. I got U3: 13.85 & 8.92, U2: 12.67 & 4.965, and U1: 3.295 & 6.93. I tested them a few more times and got nearly the same values. I can't say I understand the reading for U1."

    U1 should be +3.3Vdc You have 3.295
    U2 should be +5Vdc You have 4.965
    U3 should be -5Vdc You have 8.92

    i think you should retest and repost please.

    nosaj
    You read my comment incorrectly. U1 didn't have an output of 3.295, that was the input figure. Output was 6.93. If U1 regulates a +3.3V and my readings are showing a +3.6, sounds close enough. U3 is a -5V, mine shows -4.9v, again sounds good. U2 should be +5v, mine is regulating 12.67 in down to 4.965 out: -7.7v....

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    Quote Originally Posted by stevenrb718 View Post
    You read my comment incorrectly. U1 didn't have an output of 3.295, that was the input figure. Output was 6.93. If U1 regulates a +3.3V and my readings are showing a +3.6, sounds close enough. U3 is a -5V, mine shows -4.9v, again sounds good. U2 should be +5v, mine is regulating 12.67 in down to 4.965 out: -7.7v....
    You cannot input 3.295 and get output of 6.93.. grab a datasheet the input output pins change.
    This makes no sense
    U2 should be +5v, mine is regulating 12.67 in down to 4.965 out: -7.7v What does the meter say 4.965 or 7.7.. just give us what the meter reads , not the subtractions between the 2 values.

    Thanks,
    nosaj

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    Quote Originally Posted by nosaj View Post
    grab a datasheet the input output pins change.
    Don't even need the datasheet, the schematic calls out the pin numbers, 1,2, and 3. You can see all 3 regulators have outputs at different pin numbers.
    I think we are all in agreement about U1 and U2 being ok.
    Need voltage readings for U3 pins 2 (input) and 3 (output). They should both be negative voltages.

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    Quote Originally Posted by g1 View Post
    Don't even need the datasheet, the schematic calls out the pin numbers, 1,2, and 3. You can see all 3 regulators have outputs at different pin numbers.
    I think we are all in agreement about U1 and U2 being ok.
    Need voltage readings for U3 pins 2 (input) and 3 (output). They should both be negative voltages.
    Just second nature to tell someone that. like finding the schematic.

    nosaj

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    Quote Originally Posted by Mark Hammer View Post
    I repaired one last year. And if memory serves, it was a burnt regulator. Those older units, like many digital devices of that era, used more current than recent devices do. The heat-sinking on the 3-pin regulators was fairly modest, and it is also easy to imagine the thermal compound coupling the regulator to the heatsink drying out over time, allowing one or more of the regulators to overheat and burnt out. I'm not saying that is necessarily what it is, but based on my own experience, that's a good place to start. Check the state of the thermal compound as well.

    Click image for larger version. 

Name:	mainpcb.jpg 
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    Earlier this year, I repaired a Diamond Memory Lane pedal for a buddy, and it took several e-mail exchanges with the company's tech support until their tech guy remembered that in one of the earliest runs of the pedal, the distributor they bought their regulators from had sent them a pile of defective regulators, whose heat sink tab was about 1/3 the normal thickness. When they'd power up the pedals to calibrate them, they'd test fine. But because the heatsink was so thin, and the regulator was free-standing without additional heatsinking, it would begin to overheat after about 15 minutes, and drift off-spec, yielding a very annoyingly audible HF whine. Since I imagine they'd set up and calibrate the pedals in less time than that, it took them a while (and probably some customer feedback) to identify the source of the problem.

    Three-pin regulators are wonderful things, but they all demand certain thermal conditions to show their best.
    The pins on the 7905 are different than the other regulators. So after a re-test knowing that, U3 gave an input of -13.76v and an output of -4.95v. Looks like the regulators are giving proper power. Which leaves me stuck again.

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    Quote Originally Posted by stevenrb718 View Post
    The pins on the 7905 are different than the other regulators. So after a re-test knowing that, U3 gave an input of -13.76v and an output of -4.95v. Looks like the regulators are giving proper power. Which leaves me stuck again.
    Ok time to follow where power should go. Based on the blink first I would find CS4224 check pin 18 for +5vdc.
    I would suggest as a learning experiment to pick a chip on pcb then google search the datasheet for it. ex jrc4558 to see which pins are power .
    nosaj

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    The bill of materials show U6 as a CS4224 but U6 in mine is a CS4221.

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    Quote Originally Posted by stevenrb718 View Post
    The bill of materials show U6 as a CS4224 but U6 in mine is a CS4221.
    Pull the datasheet and see if you can spot the difference between the IC's.

    nosaj

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    giving about 4.7v

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