DO you really want to try to replace the MCU if it's "blown"? How, without an oscilloscope, can you figure out which component it is that's "blown"? I have to agree with Erik ... if you have only one board, and no oscilloscope, you'll never know what's wrong. You'll always wonder if that last "foolish" thing you tried did some damage.

I'd suggest that you reconsider what I previously mentioned, and acquire a used TEK 475A with DM44 which provides you with the oscilloscope and multimeter, and even a thermal probe if you need it, and then proceed.

I'd suggest you might want to try a non-Atmel MCU for which the serial-port programmer circuit is well defined, e.g. one of the MAXIM/Dallas DS89C4x0's, of which you can probably get a free sample or two just for the asking, or a NXP or or other series not as widely divergent from a programming standard as the ATMEL series. Once you get established, you can deal with supply chain issues. It's seemingly foolish to buy things in India, as they're usually vastly overpriced and supply issues frequently arise, as the vendors don't know what they're selling.

To get started, I'd recommend you stay away from parts in other-thanDIL-40 packaging, as the surplus market still contains many of them, though they're not popular for production any longer. If, for some reason, you can't find such a thing anywhere, even online, then email me and I'll send you a couple, perhaps even including an old standard 8751. With those you can do anything that's documented in their datasheet, can program them in ASM, or in 'C' if you prefer and have the tools, and can rely on the datasheet. That's not always possible with ATMEL.

RE