Unofficial Nextion/TJC User Forum

No more serial comm after reverse polarity - Help!

I’ve a 3.5 enhanced unit that I erroneously powered in reverse. The display and touch screen still work, but serial comms seem to be dead.

Things I’ve checked:

  • Project upload via SD card – WORKS
  • Project upload via USB to TTL – DOES NOT CONNECT
  • Arduino project that works with working replacement Nextion – NO SERIAL COMMS

Does anyone have ideas/suggestions of things I could look at to repair this unit?

Thanks in advance,

Welcome @stever519!

Serial coms go straight to the main microcontroller itself. Assuming that one is not damaged (otherwise game over), I suggest the following:

  • Scope the 3.3V line to make sure the regulator is still working properly. Badly regulated 3.3V could cause such issues
  • Scope the serial lines to see if anything happens at all (and if so, what). Especially during startup Nextion should transmit some default values (as defined in the Nextion Instruction Set).

Kind regards,

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