# 3.3v pro mini can only load sketch once **URL:** \ **Category:** Programming\ **Created:** [January 10, 2018, 4:07am UTC](https://forum.arduino.cc/t/3-3v-pro-mini-can-only-load-sketch-once/501275 "2018-01-10T04:07:24Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![gobo770](https://avatars.discourse-cdn.com/v4/letter/g/dfb087/32.png) [@gobo770](https://forum.arduino.cc/u/gobo770)\ **Post date:** [January 10, 2018, 4:07am UTC](https://forum.arduino.cc/t/3-3v-pro-mini-can-only-load-sketch-once/501275/1 "2018-01-10T04:07:24Z")
was working with a 3.3v pro mini (clone,) damaged the cpu and replaced it. burned the boot loader from the arduino ide using a usbtiny. i can upload a sketch only once. additional attempts to upload a sketch result in "programmer not responding". as long as i reload the bootloader, i can upload any sketch on the first attempt. my first guess was fuse settings. so i captured the avrdude bootloader output and the fuses are as listed in the boards.txt file. unlock = 0x3f lock = 0x0f low = 0xff high = 0xda ext = 0x05 using arduino v1.6.9 on an older linux system. i have run out of ideas. any suggestions? thanks! ---
**Author:** ![6v6gt](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/6v6gt/32/225488_2.png) [@6v6gt](https://forum.arduino.cc/u/6v6gt)\ **Post date:** [January 10, 2018, 4:58am UTC](https://forum.arduino.cc/t/3-3v-pro-mini-can-only-load-sketch-once/501275/2 "2018-01-10T04:58:47Z")
Once you have successfully burned the bootloader onto the pro mini using the USBtiny, what are you then using to upload your sketch to the pro mini ? ---
**Author:** ![pert](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/pert/32/217111_2.png) [@pert](https://forum.arduino.cc/u/pert)\ **Post date:** [January 10, 2018, 5:19am UTC](https://forum.arduino.cc/t/3-3v-pro-mini-can-only-load-sketch-once/501275/3 "2018-01-10T05:19:14Z")
Typically "only can upload once" means the auto-reset is not happening. When the serial connection to the Pro Mini is made it should automatically reset, which puts it temporarily in a state of listening for a sketch to be uploaded. After burning the bootloader it is constantly in that state so a reset is not needed to do a reset on that first upload. ---
**Author:** ![gobo770](https://avatars.discourse-cdn.com/v4/letter/g/dfb087/32.png) [@gobo770](https://forum.arduino.cc/u/gobo770)\ **Post date:** [January 10, 2018, 2:54pm UTC](https://forum.arduino.cc/t/3-3v-pro-mini-can-only-load-sketch-once/501275/4 "2018-01-10T14:54:19Z")
using the same 3.3v ftdi serial board to download the sketches before i blew up the cpu. killed the cpu by fumbling around and allowing a 12v jumper touch something on the cpu (i was working on a 3.3v logic input high-side driver.) this might have damaged the ftdi, i just assumed it was ok as the first upload works. i'm confused about the auto-reset initial handshake. after the bootloader is flashed, the board goes into the default pin blink that i assumed was included as part of the bootloader. (the chip has been erased with avrdude command line. the only file on the bootloader log is ATmegaBoot\_168\_atmega328\_pro\_8MHZ.hex.) so how is the auto-reset initiated after a first upload? is this done by the ftdi dtr pin? ---
**Author:** ![anon57585045](https://avatars.discourse-cdn.com/v4/letter/a/ed8c4c/32.png) [@anon57585045](https://forum.arduino.cc/u/anon57585045)\ **Post date:** [January 10, 2018, 3:14pm UTC](https://forum.arduino.cc/t/3-3v-pro-mini-can-only-load-sketch-once/501275/5 "2018-01-10T15:14:56Z")
> gobo770: > so how is the auto-reset initiated after a first upload? is this done by the ftdi dtr pin? Yes ---
**Author:** ![pert](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/pert/32/217111_2.png) [@pert](https://forum.arduino.cc/u/pert)\ **Post date:** [January 10, 2018, 3:22pm UTC](https://forum.arduino.cc/t/3-3v-pro-mini-can-only-load-sketch-once/501275/6 "2018-01-10T15:22:04Z")
You should be able to manually reset the board just as the reset is happening but you have to get the timing right because the bootloader is only active for a short amount of time before the sketch starts running. ---
**Author:** ![gobo770](https://avatars.discourse-cdn.com/v4/letter/g/dfb087/32.png) [@gobo770](https://forum.arduino.cc/u/gobo770)\ **Post date:** [January 12, 2018, 4:21pm UTC](https://forum.arduino.cc/t/3-3v-pro-mini-can-only-load-sketch-once/501275/7 "2018-01-12T16:21:17Z")
knowing that the bootloader is in a listening state after flashing was the key. a cold solder joint existed on the reset line coupling cap. once i figured out which one it was, pushing down on it a scope probe and uploading at the same time would allow the upload. don't know if this is due to being a lowest cost board or a result of my hot air pencil removing the cpu. thanks for the suggestions! ---
**Author:** ![system](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/system/32/1140315_2.png) [@system](https://forum.arduino.cc/u/system)\ **Post date:** [May 5, 2021, 10:56pm UTC](https://forum.arduino.cc/t/3-3v-pro-mini-can-only-load-sketch-once/501275/8 "2021-05-05T22:56:17Z")