I would start by testing your wiring for continuity with your voltmeter. The continuity setting will be the one that will make an audible noise when you touch the leads together. This tests your wiring connections to ensure current is flowing between components. If there is a solid connection, you'll hear a beep. You'll be able to detect if you have faulty solder joints or bad components. Make sure your pots are turned on fully when testing.
Check out youtube vids to see how to check continuity if you need some guidance. This is one of the most basic and useful skills using your voltmeter.