Charger displays E20 internal power supply error; LEDs may be dim or flicker, unit may reboot repeatedly.

Safety first: Turn off power at the breaker and wait for capacitors to discharge before touching internal components.

• Visual inspection: Open the unit and inspect the low-voltage power supply area (often a small transformer or switching supply). Look for bulging capacitors, burn marks, or cracked components.
• Check low-voltage connectors: Ensure any plug-in connectors from the power supply section to the logic board are firmly seated.
• Minimal load test (advanced): Disconnect non-essential peripherals (Wi-Fi module, RFID reader) and see if the unit stabilizes. If it does, one of those modules may be shorted and need replacement.
• Measure low-voltage rails (qualified person): With great care and appropriate tools, a technician can measure 5 V / 12 V rails on the board. Out-of-spec voltages confirm a failed supply.
• Board replacement: In most JuiceBox designs, the low-voltage supply is integrated into the main control board, which must be replaced as a whole.