I'm working on a few guitar pedal circuits that include discontinued components (BBDs, corresponding clock chips, some companders, etc.). I'm happy to second-guess myself in terms of how I have things set up, but I'm increasingly confident some of the new-old-stock parts I got from eBay or Amazon merchants are defective. So I have two questions:
1. Are there general starting points for testing IC's, or will pretty much everything be entirely case by case? If the former, where do y'all usually begin?
2. Are IC failure modes generally obvious, or could all the testable voltages, resistances, etc. look good and the chip still be junk?