Programming Arduino Mega 2560 USB-Serial

Okay, some time ago, I posted about a Mega 2560 which was giving me some grief. I've since purchased a few more of these boards, but want to see if I can resurrect the dead one by attempting reprogramming the USB to Serial

I do see the programmer interface on it, and am assuming that the interface the same pinout as the one for the bootloader programmer.

What I don't know is where do I get the firmware for it, and what do I use?

I had ordered a USB programmer, it should have been here by now, but isn't. I think that there's been a problem with the post (or maybe seller forgot to actually ship it, who knows...) Anyway, if the board can be made useful again, that'd be great.

To recap the original problem:

Arduino Mega 2560 r3, using RAMPS 1.4 shield for 3D printer, was working, then stopped. unable to load sketches, with avrdude reporting:

avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_getsync(): timeout communicating with programmer

Attempted loopback test, fail result. (Have since done loopback test on a new arduino mega 2560, and (no surprise) passed, so I'm quite certain that I performed test correctly. Re-ran test on failed board, still failed.

I'd been give the advise of reprogramming the 16U2. can I use the functional arduino as an ISP programmer to attempt this, or will I need a different ISP programmer? the Amtel "flip" software was recommended, but before downloading it, I'd like some foreknowledge of chances of success. I don't know if "arduinoISP" is a supported programmer for the serial controller.

I'm also not 100% certain that anything can bring back the arduino, but if the risk of destroying ANOTHER arduino is minimal, or at least less than the chances of restoring the unusable one, I'll give it a shot. Forewarned is forearmed after all.