I know this question has been asked multiple times but solutions giving there hasn't been working,

I've got an esp32 soldered to my own designed PCB board with a UART to USB converter all that is working fine, I can get connected to my esp from the Serial monitor.

But it prints every about 0.5s:

boot:0x13 (SPI_FAST_FLASH_BOOT) 
flash read err, 1000 ets_main.c 
371 ets Jun 8 2016 00:22:57

Solutions have been to make sure to have 3.3v on the esp. I find it unlikely to have anything to do with it, 'cause its voltage range goes from 2.6v to 3.6v, but anyway I have tested it with an advanced transformer and a multimeter to check that there was 3.3v on the Vcc pin (didn't change anything).

All help would be appreciated.

Here is a bit more info:

I've also connected a 10uF capacitor (someone told me to try that).

If I pull IO0 to ground, it prints waiting for download in the serial monitor and I can almost upload the program, this is what I get:

enter image description here


(I have checked with multimeter)

PCB board:

enter image description here

enter image description here

enter image description here

  • 1
    Please provide images of your custom PCB
    – Majenko
    Jul 30, 2019 at 13:16
  • I had this kind of error sometimes and it always seemed to be related to a broken flash in the esp32. Do you have anything connected to the SPI pins?
    – Sim Son
    Jul 30, 2019 at 15:45
  • @SimSon could you explain what the SPI pins is? (sorry for my lack of knowledge) Jul 30, 2019 at 15:47
  • The esp chip itself doesn't have an internal flash to store the program but uses an external flash instead. Communication with this flash happens via serial peripheral interface (SPI) which also is available on the esp's pins. Obviously you haven't connected anything except the serial lines.
    – Sim Son
    Jul 30, 2019 at 15:54
  • How did you assemble the esp on that pcb? Reflow? Solder iron? I just wonder why the surface looks a bit demolished...
    – Sim Son
    Jul 30, 2019 at 15:56

2 Answers 2


Your PCB is lacking in the majority of things you need to get the module working. These modules are not "simple" in that you provide power and forget about it. You must add all the required support components. Those support components are NOT optional. For example: you aren't setting the boot mode properly with the right pullups. You lack a capacitor on the power pins (I told you to add one already. Where is it?). Also your power traces are too thin. The impedance is too high.

  • there is a 10uF capacitor added, its the second black and red wire you see on the image, I have moved it directly on the power pins, still not working Jul 31, 2019 at 11:40
  • and what do you mean by "I'm not setting the boot mode properly", serial monitor literally says it's in boot mode Jul 31, 2019 at 11:42
  • There's many ways of booting the ESP32. You haven't selected one. Read section 2.4 "Strapping Pins" in the ESP32 datasheet.
    – Majenko
    Jul 31, 2019 at 11:50
  • And you can't have a decoupling capacitor on the end of a pair of wires. It makes it pointless. Solder it directly on to the power pins of the module. photos.app.goo.gl/rjTESshnQGQjjtmdA
    – Majenko
    Jul 31, 2019 at 12:03

ok, the solution was to add a 10k pull-up resistor to the EN pin, as shown HERE

No capacitor needed

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