So, you don't want to check/replace those capacitors.
OK, let's hope they are good. I won't try to convince you any more how a high ESR in filtering capacitor can make the microcontroller clock to not start, or how on the power line oscillations of many hundreds of kHz or even MHz can arise and make the microcontroller to not work.
You just want to know how to download the firmware. Let's say you downloaded it, and you compare with the other working GM328. Then, they are different. Does this means that the other GM328 has a different firmware, or does it means the old GM328 firmware was damaged? Let's say the former. You see byte 74 is differnt on the 4th bit. Now what? What understanding does this bring?
If you are not willing to follow directions, and don't need general advice, then just ask a very specific question, for example "how to download firmware from an ATmega328 using an Arduino nano?". Most probably it won't be possible, because AVR chips, like ATmega328, can be protected against reading the firmware, so one can protect its programs against unauthorized copying.
Go to the github page
blurpy gave you,
https://github.com/blurpy/transistor-tester , click on the "CODE" button, then click "Download ZIP". Save it locally and unzip. Now you have the whole project locally, including the already compiled hex. If you read the readme files you'll find this, as already told:
Original GM328 firmware
The GM328 AY-AT comes with the fuses of the ATmega328P configured in read protected mode,
meaning we can not backup the firmware. Trying to read the chip will only result in files filled with
the value FF. One user was lucky and got an unprotected chip, and uploaded the firmware (v1.12k)
here. The files are also available in this folder
Meaning it shouldn't be possible to download the firmware.
However, it is possible to overwrite another firmware, as advised.
Beware that there are 3 things that can be written in an ATmega328
- the fuses (or fuse bits)
- the program (the executable firmware)
- the EEPROM (the data flash)
You can find them all already compiled in the "transistor-tester-master/firmware/original" folder. The exact location of the avrdude programmer software depends of your OS and your local install path for Arduino IDE. To find it, search on your local disk "avrdude". Usually is in "hardware/tools/avr/bin/". If you are using windows it might be "avrdude.exe" instead of just "avrdude", IDK.
Since the MCU is on a socket, remove it, place it on a separate breadboard, and see if this PDF has enough detail to read the chip.
https://app.box.com/s/ol1z8jjnrpy6wly4w61imt7wcbxk3fcgGood luck with it.