upload, reset, loopback trouble on mega2560

Development Tools IDE 1.x
1

hi all!
i'll explain some trouble i'm having with mega2560, trying to summarize as more as possible!

uploading the first sketch about stepper, the board worked, UNTIL once i saw some strange codes in the serial monitor window! After that, i can't upload anything on my 2560 :~

the loop-back test, doesn't work but i think there is something bad with reset, because when i connect a reset pin with a ground pin nothing happens but led flash once.

in few days, i'll got another 2560 (that i bought before these trobules XD) and i will try to:

  1. reburn bootloader
  2. reflash 16U firmware

Do anyone understand something more than me? :smiley:

PS: i hope my english is quite decorous :.

2

no idea? :frowning:

3

UPDATE:
i succesfully burnt the bootloader with another Mega 2560!

but now the L led is always blinking, and i can't upload any sketch!

someone can help me? =(

4

UPDATE 2:

following this thread [SOLVED] Sketch upload failed after (maybe) shorting pins to 12VDC - IDE 1.x - Arduino Forum, i checked the resistor value (resistance and voltage) and it is good.

However, I found something strange in the resistors between USB and ATMEGA 16U2 (attached image): the first one on the top, with USB power disconnected, has a "normal" ohm value, 220 ohm. With the USB plugged, it says 920-930 ohm!

I thought i can try to shortcircuit that resistor with another 220 ohm...what do you think about??

resistors.png