Simple envelope, I built two, one is acting up

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General advice for troubleshooting a module and asking for help

(This is a wiki post, please add and correct!) Look and see if others have had the same problem. Use the Discourse search facility to find topics where the module you’re building is discussed. Inspect your work. Verify all components are correct values. Look for solder connections that are rough, irregular, skimpy, dull, or missed completely (we all do that!) and reflow them. Look for solder bridges between pads and remove them. Check your power connection. If it’s a Eurorack style power cabl…