Sometimes the unit freezes on the "Roland Juno-Di" splash screen. While this is often a firmware issue, it can be a hardware fault in the flash memory.
Service manual solution: The manual explains how to enter the Test Mode (usually holding specific keys while powering on) to rewrite the firmware or run a memory check. roland juno di service manual work
The Juno-Di uses rubber contact strips (rubber mats) under the keys. Sometimes the unit freezes on the "Roland Juno-Di"
The manual shows a cross-section of the key mechanism. Each key has a pivot pin and a return spring. You will see a white plastic strip running the length of the keybed—this is the "key slip" prevention bar. Remove it. Then, gently lift the faulty key from the front edge, angling it toward the back. The Juno-Di uses rubber contact strips (rubber mats)