Burnt out USB charger


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




  • 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


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


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s