Atmega2560 Pro Embed no sketch upload possible (timeout)

Using Arduino Avrdude, stk500, Bootloader issues
1

It's this board.

Things I tried: Serial loopback test checks out okay.
I can read fuses (which are the standard setup for the Mega 2560), I can program the bootloader (newer bootloader double flashes the LED, old bootloader flashed just once per second). I used an USBASP for both.
I'm using Arduino 1.8.13.

I can't seem to program it directly through serial either.
Nanos using the same serial chip work fine, so it's not the driver.
Tried multiple cables, multiple ports. I can see that it resets the atmega to program since the LED freezes until timing out.

Error is always

avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_getsync(): timeout communicating with programmer
An error occurred while uploading the sketch

Any ideas on how to program these guys? Is there some sort of test hex I could try to flash directly via ISP?

2

what old and new bootloader? there is only one bootloader for Mega 2560 in Arduino AVR boards packages.

you can upload any sketch over ISP with "Upload using programmer" in Sketch menu

3

Old and new relative to the one that was originally on there and the one I flashed via the Arduino IDE.

4

arakon:
Old and new relative to the one that was originally on there and the one I flashed via the Arduino IDE.

new boards have Blink sketch uploaded. that blinks every second.

how did you burn "the one that was originally on there"?

5

I didn't, that was just that was on there. I assumed the blinking was caused by the bootloader already on there.

I just uploaded the blink sketch with the addition of a serial output, over ISP.
It uploads and runs. Serial output is there too. I also checked the connectivity with a multimeter and all pins check out for serial.

I did however also run a sketch that should take input from the serial monitor and send it back (while also changing the blink speed of the LED) and that doesn't seem to work. It outputs, but doesn't take inputs.. same sketch is fine on a nano.

I suppose that means the RX pin is blown on the Atmega itself. Just my luck.

6

please make sure that your rx tx pins have nothing else hooked up during upload process

7

They don't, it's just the blank board with nothing attached at all.