Use this forum to chat about hardware specific topics for the ESP8266 (peripherals, memory, clocks, JTAG, programming)

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By Ashram56
#93745 Good morning,

I have a very odd behaviour I'd like to get clarification on:
- custom PCB using an ESP12F, which was working fine before, suddenly stopped working
- after multiple investigations (reflashing using FTD32, etc), I realized that GPIO0 pin reading was at 1.9V (GPIO2 was at 3.3V)
- Schematics are super simple: these two inputs are pulled-up to 3.3V. When measuring on PSU side of the resistor I see a nice 3.3V, when measuring at ESP side of the resistor, 1.9V

That would explain why the ESP does not boot, since I assume it's entering flash mode (1.9V is just below TTL level)

But now... why in the world would the ESP input try to drive this signal low ? I can only think of a defective input, but that seems a stretch (ESD damage maybe ? I was indeed manipulating the board at one point, but did not mishandled it though)