18V Danelectro Cool Cat Chorus gate problem

[stevenrb718]

I have an 18v Danelectro Cool Cat Chorus pedal where the effect works for a few seconds and then stops "effecting" as if a gate is switched on. The unaffected signal continues to ring. When striking the strings again, the signal will be back to the Chorus effect for a few moments. I've seen a few blogs in the past with the same issue as mine, but I never saw a fix for it. Any ideas?

[Mark Hammer]

All bucket-brigade circuits require the audio signal to "ride in" to the delay chip atop a DC bias voltage. Here is one example of that in action. https://www.hobby-hour.com/electroni...f2-flanger.php YOur chorus should be fairly similar to much of this circuit. The delay chip is IC3. You can see that the input signal comes in to the chip on pin 3, but there is also a bias voltage joining the audio signal via R17 (100k). There is a 1uf cap to ground from the wiper of that trimpot.(C11). IF there was something amiss with C11 such that its value was not stable, you would expect the functionality of the delay chip to vary over time, conceivably starting out okay, but drifting off-spec. If I am correct, then replacing the analogous cap on your Chorus should, in theory, restore functionality. The question is WHICH cap is it?


Here is a gutshot of the Cool Cat Chorus that I found. I assume it looks like yours. I see two orange trimmers, but don't know which adjusts the bias voltage. You could tell by tracing the path from pin 3 on the MN3007 chip back to the wiper of one of them.. The cap in question should, in theory,, be connected to the wiper of that trimmer.

[stevenrb718]

All bucket-brigade circuits require the audio signal to "ride in" to the delay chip atop a DC bias voltage. Here is one example of that in action. https://www.hobby-hour.com/electroni...f2-flanger.php YOur chorus should be fairly similar to much of this circuit. The delay chip is IC3. You can see that the input signal comes in to the chip on pin 3, but there is also a bias voltage joining the audio signal via R17 (100k). There is a 1uf cap to ground from the wiper of that trimpot.(C11). IF there was something amiss with C11 such that its value was not stable, you would expect the functionality of the delay chip to vary over time, conceivably starting out okay, but drifting off-spec. If I am correct, then replacing the analogous cap on your Chorus should, in theory, restore functionality. The question is WHICH cap is it?


Here is a gutshot of the Cool Cat Chorus that I found. I assume it looks like yours. I see two orange trimmers, but don't know which adjusts the bias voltage. You could tell by tracing the path from pin 3 on the MN3007 chip back to the wiper of one of them.. The cap in question should, in theory,, be connected to the wiper of that trimmer.

That's exactly the PCB layout as mine. Unfortunately I already swapped the capacitors as several were out of spec. Another weird symptom that I'm just now getting is the effect switching doesn't always seem to work, yet the physical switch itself tests fine. I could push the switch a hundred times without the effect coming back on. When I unplug and plug it back in, sometimes that corrects it.

[Mark Hammer]

The 14-pin chip just below the switch appears to be a 4013 flip-flop, that is likely an essential part of the engage/bypass circuitry. Such CMOS chips can be easily damaged, and render a pedal nonfunctional or intermittent in some ways. If you have easy access to a local parts distributor, consider replacing that chip, being mindful to avoid any static discharge, heat-related damage during installation, and being sure to orient it properly.

I'll just note that CMOS chips do not like to be powered by more than 15V, so if you did try to power the pedal with 18V, you might have damaged it.