Hello everyone, i'm new to this forum so forgive any mistake 
I got an arduino uno R3 SMD, when i plugged it there wasn't any firmware so i put it on with flip. Then i tried to upload a program, RX blinked 3 times (L stayed always on) and got an error (avrdude: stk500_getsync(): not in sync: resp=0x00). I realized that there wasn't any bootloader so i put it on with another arduino board. Now when i try to upload a program L blinks as it does in the other board when uploading, but RX still blinks 3 times and i get the same error. I can upload the program with the other arduino as isp and it get executed but i'd like to use the usb interface. What can i do? Thanks!
This is the complete error:
C:\Program Files (x86)\Arduino\hardware/tools/avr/bin/avrdude -CC:\Program Files (x86)\Arduino\hardware/tools/avr/etc/avrdude.conf -v -v -v -v -patmega328p -carduino -P\.\COM5 -b115200 -D -Uflash:w:C:\Users\ALESSA~1\AppData\Local\Temp\build8783361213569724924.tmp\Blink.cpp.hex:i
avrdude: Version 5.11, compiled on Sep 2 2011 at 19:38:36
Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/
Copyright (c) 2007-2009 Joerg Wunsch
System wide configuration file is "C:\Program Files (x86)\Arduino\hardware/tools/avr/etc/avrdude.conf"
Using Port : \.\COM5
Using Programmer : arduino
Overriding Baud Rate : 115200
avrdude: Send: 0 [30] [20]
avrdude: Send: 0 [30] [20]
avrdude: Send: 0 [30] [20]
avrdude: Recv:
avrdude: stk500_getsync(): not in sync: resp=0x00
avrdude done. Thank you.
Resetting the board during upload didn't solve anything. Also i just noticed that the two RESET EN pins are shorted. Is this the cause of the problem?
Any solution would be appreciated. Thanks.
Firstly if you bought a board it should have had bootloaders and firmware on it.
Secondly the biggest source of these errors is uploading to a not connected com port, as in one that does not have an Arduino on it.
change your laptop to airplane mode then ports will work ....code will be uploaded....
I only have two ports: COM1 (my serial port) and COM5 (the arduino port) so i can't upload to the wrong port.
My pc is a tower with ethernet connection so i think it isn't that the problem (as the other board works).
The problem is in the atmega16u2 but i can't find it out. I tried both usbserial and usbdfu drivers without success.
Can you post a link to where you bought the board from?
I bought it from a guy at the electronics fair, i don't know if he has a website.
What makes you think there wasn't any firmware on the board?
When i plugged the board for the first time, it wasn't seen as arduino uno but atmega16u2 dfu. Now there is usbdfu combined firmware, but i can't upload through the usb port (also tried usbserial).
OK... so what have you done to check the firmware on the Atmega328?
You mean the bootloader? It was missing too because the L led didn't blink when powering the arduino. I burned it using the other arduino as ISP.