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Digitech Whammy IV Problem

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  • stevenrb718
    replied
    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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  • g1
    replied
    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.

    Leave a comment:


  • stevenrb718
    replied
    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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  • g1
    replied
    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)

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  • stevenrb718
    replied
    No more ideas?

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  • stevenrb718
    replied
    giving about 4.7v

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  • nosaj
    replied
    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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  • stevenrb718
    replied
    The bill of materials show U6 as a CS4224 but U6 in mine is a CS4221.

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  • nosaj
    replied
    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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  • stevenrb718
    replied
    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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  • nosaj
    replied
    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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  • g1
    replied
    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.

    Leave a comment:


  • nosaj
    replied
    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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  • stevenrb718
    replied
    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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  • nosaj
    replied
    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

    Leave a comment:

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