Burnt out USB charger

Preamble

It’s one of those horrifically dangerous 2.5×2.5×2.5 cm mini-cube singe port 1 A USB chargers. There were scorch marks on the base of the case. The circuit was very simple, a simplified SMPS on two small PCBs… which held into the cube casing with white silicone/glue – scratch that away and it is easy to extract the pair of PCBs

Links

Gallery

Components

  • Resistors
    • R1 Measured 12 Ω  – PCB1 (brown red black – 12 Ω)
    • R2 Measured 8Ω or 3.5MΩ – PCB1 (orange blue green – 3.6 MΩ)
    • R3 Measured 470 Ω – PCB1 (yellow purple brown – 470 Ω)
    • R4 Measured 127 Ω – PCB2 (yellow purple brown 470 Ω?)
  • Capacitors (ceramic) – PCB1
    • C1 ?unreadable – 102 (1 nF) (202?UNLIKELY)
    • C2 472 (4.7 nF)
  • Electrolytic
    • 2.2 µF 400V – PCB1
    • 220 µF 10V – PCB2
  • Diode
    • D1 1N4007 – PCB1
    • D2 N58/M (1N58*?) – PCB2
  • Zener
    • PCB2
  • Transformer
    • ?no markings
  • Transistors
    • C945/P331
    • 13001
  • Optocouple
    • 817/D520

Additional notes

  • Two resistors, R4 and R5, were missing on the PCB2, possibly for Apple support.
  • USB 2 and 3 were shorted

The Issue

was the Zener diode. The clues were that the case was scorched, next to the Zener, and the PCB was blackened beneath the Zener. Also, when the Zener was magnified, then it could be seen to be visibly cracked in in the middle, due to the heat that it had been exposed to.

Burnt Zener diode

Schematic

On GitLab: https://gitlab.com/testkins/burnt-out-usb-charger

 

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