Mega R3 doesn't show up in device manager, not even unrecognized device

So I have this Arduino, it was working about a month ago – I swear I didn’t do anything to it, and now it doesn’t seem to work.

When I plug it in, nothing happens, no sounds, no “looking for drivers”, not even an unrecognized device in windows device manager.

If I use ICSP with my stk500v2 and avrdude, I can flash the bootloader onto the main AT MEGA 256 chip.

It looks like there is another ICSP header near the ATMEGA 16u2 chip, and I tested it with a multimeter, it seems to have VCC and GND in the correct places. – I tried grounding the reset pin to see if it would do anything (while it was plugged into USB), nothing happened.

I found this “Arduino-COMBINED-dfu-usbserial-atmega16u2-Mega2560-Rev3.hex” hex file and figured I would try to upload it, but, I just can’t make the damn thing work.

For a while the device signature was coming up with completely random and unique signatures every time, and now it just comes up with 0x000000 every single time, and additionally now it comes up with unknown status codes:

avrdude.exe: stk500v2_command(): unknown status 0x80
avrdude.exe: stk500v2_command(): unknown status 0xc9
avrdude.exe: stk500v2_program_enable(): cannot get connection status
avrdude.exe: initialization failed, rc=-1
avrdude.exe: AVR device initialized and ready to accept instructions
avrdude.exe: Device signature = 0x000000
avrdude.exe: Yikes!  Invalid device signature.
avrdude.exe: Expected signature for AT90USB162 is 1E 94 82

I’m really not sure what to do here. Is the 16u2 bricked, or is there something else I can try?

Even if the 16u2 is bricked, the rest of the board works, and can be programmed with my ICSP programmer… – but I plan to use it as a RAMPS board for a 3D printer – so it will need serial communication – is it possible to hook up an FTDI board somewhere and bypass the 16u2 all together?

It seems that the ATmega16U2 is broken. Perhaps there was a static electricity voltage spike when you connected the usb. You could try to replace the crystal of the ATmega16U2, I don't think it will help though.

Is it an official Arduino Mega 2560 R3 board ? or a cheap clone with bad quality components ?

When you are willing to upload a sketch via the programmer, you can use it. But you can't use pin 0 or 1. There are three other serial ports that you can use and connect a usb-serial module to. The bootloader uses the first serial port at pin 0 and 1. If you want to upload a sketch via another serial port, you have to build a new bootloader.

It's a clone. "Iduino Mega R3".

Weirdly, it's working now... kind of at random.

Here's what I did (in the hopes that maybe someone else with the same problem will be helped by this).

I uploaded a Marlin firmware for reprap (from the Arduino IDE using the "Upload using programmer" option), and then I disconnected it.

I connected it to 12v+ power on the barrel jack -- nothing to USB. (I don't recommend this, it eventually got really hot and I had to unplug it, but who knows, maybe the board is so flakey that this was part of the solution.)

I hooked an FTDI up to RX/TX pins 0 and 1 (the ones you said won't work -- and you're right they totally didn't work) -- I also hooked the FTDI up to GND, and hooked DTR up to the reset pin, and tried to play around with getting it to talk in the Repetier Host program. -- It never really did anything, but I screwed around with it a bit. -- I may have connected a few things wrong at some point.

When I noticed the board was getting really hot (from the 12v supply, whoops), I unplugged it from everything, waited a few minutes, and switched it to USB power, and then windows was all like "beep beep boop!", and then I was all like "O.O".

To be on the safe side, I switched over to a 5v supply, and hooked the ICSP up to the 16u2 and flashed the latest combined firmware anyway (I wonder if the existing flash had like a bad byte or something somewhere, and it was causing it to be flakey).

Man, I am never buying a knock off board again, I wasted a whole evening to this piece of crap. $40 more dollars on the real deal would have been well spent. :roll_eyes:

One question : To which pin or connector did you connect the 5V supply ?

For the 5v supplies I used both regular USB cables, and the barrel jack. For 12v (which I should not have been using, but did anyway), I only used the barrel jack.

EDIT: Rereading my earlier post, apparently, I wrote "power shield" instead of "barrel jack" -- I've updated the original post to make it more clear -- I can totally see how that could be misleading, since "shield" means something specific to Arduino folks. As a point of clarification: I performed all of the above steps on the lone Arduino board, with no actual shields connected to it, not even the RAMPS shield.

5V to the usb connector is okay. 7.5V or more to the power barrel jack is okay. If you apply 12V to the power jack, the voltage regulator might get hot. If you can't keep your finger on the voltage regulator, it is too hot.

Be careful when using 5...7.5V to the power jack. When it is below the 7.2V, the usb power is not switched off, and current from the power jack could flow into the usb to the computer. It will not be above 5V, but it still is not recommended. When it is 5V to the power jack, the Arduino Uno doesn't get enough voltage. The analog values will be wrong, if the default 5V is used as reference.

For some of my projects I have a single 5V for the complete project. I apply the 5V to the 5V pin. A protection diode is added from the 5V pin to VIN pin. The applied 5V is not extremely strong (less than 1A). When I turn off my computer, the current flows into the computer. That might damage things, so it is not recommended at all.

Interesting, is the voltage regulator just a regular 7805? -- that would match up with the 7.5v figure you mentioned. -- I figured there was an smd voltage regulator on there somewhere but wasn't sure about it.

I wonder if the 5v on the power port is what confused it. I'm pretty sure it was confused / not working before when I had only plugged in the USB cable, but now I'm not sure... I'll try powering it with 7.5v from now on.

It is about the mosfet that switches on or off the usb 5V power.

The schematic is on this page : https://www.arduino.cc/en/Main/arduinoBoardMega2560 A mosfet switch is used to enable the usb 5V power. At 6.6V of VIN, this is switched off. The power jack has a diode to VIN. I assume the diode has a 0.6V voltage drop. So the minimum safe voltage at the power jack is 6.6 + 0.6 = 7.2V.

Some Arduino boards have a 7805, others have a LDO (low voltage drop regulator). The Arduino Mega 2560 version 'R3' seems to have a NCP1117, that is a LDO.

I don't think most official Arduino uses 7805. The Nano uses a version of 7805.

If has a clone, "Iduino Mega R3", the schematic won't be at the Arduino Mega page.

Same problem after one day of resetting, reinstalling, restarting I found the problem: I was using a USB power cable (with no data wiring)! ... .. . :disappointed_relieved: :'(