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Digitech Whammy IV Problem

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  • #16
    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.

    [ATTACH=CONFIG]51305[/ATTACH]

    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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    • #17
      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
      Binkie McFartnuggets‏:If we really wanted to know the meaning of life we would have fed Stephen Hawking shrooms a long time ago.

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      • #18
        The bill of materials show U6 as a CS4224 but U6 in mine is a CS4221.

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        • #19
          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
          Binkie McFartnuggets‏:If we really wanted to know the meaning of life we would have fed Stephen Hawking shrooms a long time ago.

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          • #20
            giving about 4.7v

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            • #21
              No more ideas?

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              • #22
                The CS4221 and CS4224 are almost identical, so I think you can use the schematic from post #8 above.
                Are you able to check for clock signal with a scope? It is shown MCLK at the upper right of pg.3 on schem.
                (And at pin3 of U6/CS4221)
                "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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                • #23
                  Originally posted by g1 View Post
                  The CS4221 and CS4224 are almost identical, so I think you can use the schematic from post #8 above.
                  Are you able to check for clock signal with a scope? It is shown MCLK at the upper right of pg.3 on schem.
                  (And at pin3 of U6/CS4221)
                  No unfortunately I can't.

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                  • #24
                    I think you may have gone about as far as you can without a scope.
                    It used to be fairly common for the crystal oscillators to go bad when units were dropped. That's why I asked about the 24mhz clock signal. Maybe they are more robust now, but they are cheap, like $1 or less. So it may be worth a shot to replace it.
                    It's the metal can near U9. You would need a 24MHz crystal, smd leads, in a package with the same physical dimensions.

                    Aside from that 'shot in the dark' maybe someone else will have some other ideas.
                    "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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                    • #25
                      Originally posted by g1 View Post
                      I think you may have gone about as far as you can without a scope.
                      It used to be fairly common for the crystal oscillators to go bad when units were dropped. That's why I asked about the 24mhz clock signal. Maybe they are more robust now, but they are cheap, like $1 or less. So it may be worth a shot to replace it.
                      It's the metal can near U9. You would need a 24MHz crystal, smd leads, in a package with the same physical dimensions.

                      Aside from that 'shot in the dark' maybe someone else will have some other ideas.
                      Well after finally getting the crystal in, I swapped it out and plugged it in. Initially, all the LEDs were lit on the board without change. Upon unplugging, and plugging back in, we're back to the pedal sensing LED being the only thing lit with no effect or change with knob turning or switching.

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