I fried my ATmega328p (Fixed thanks to KI6NAZ's story)

[TangoBravoMike]

Probably most people who have damaged their boards did it by zapping them with electrostatic discharge. The ISP pin header is said to be very susceptible. When I read about that I got an anti-ESD mat to work on, and I ground the mat and have the wrist strap on whenever I’m working with the boards. 20 bucks at Amazon.

But even so, I found another way to kill it. I was probing the board, under power, looking for voltage at U4 pin 26. That’s the ATmega328p ‘brain’. I was trying to figure out how the pushbuttons signal the 328p, because both my radio and [call sign deleted] The Man From Pennsylvania’s radio often don’t respond to button presses. His is worse than mine and I’d like to fix the problem. I was messing with my board, trying to see how the better one behaved.

My hand twitched a little, and my probe bridged pins 26 and 27. I'm pretty sure that's what killed it; immediately the radio was broken. The OLED display went black. VCC dropped to 0.7 volts instead of about 4.8. U4, the 328p, heated up a lot, so that’s what was pulling current. No magic smoke, but it was dead.

I’d already heard that Josh Nass KI6NAZ (YouTube “Ham Radio Crash Course”) had problems with his board and had fried his 328p. ATmega328p microcontrollers are Unobtainium everywhere (see Octopart.com) but KI6NAZ found that you can scavenge the processor from a development board
https://www.amazon.com/dp/B07X2JGS69
where you get 3 boards for about $25. Clone chip? I dunno.

Time for a brain transplant . I don’t have (or want) a hot air rework station, so I used desoldering alloy
https://www.amazon.com/dp/B00OOBIJ6I
to remove the truSDX bad chip and the donor board’s chip. Clean everything up with solder wick after heavily re-tinning the donor chip and the board to get the weird alloy off. Drench everything in flux and solder the hopefully-still-good chip onto the truSDX board. Doing this was right at the limit of what my hands are capable of accomplishing. Very small soldering.

I crossed my fingers and tried installing the bootloader and firmware to the truSDX board. It worked, and the radio is alive again, so the repair was a success.

Lesson Learned: Don’t even try to probe a fine-pitch SMD device under power. I just can't do it. Solder on a temporary test point (maybe a resistor lead clipping), preferably away from the chip – wherever the trace goes – and hook your test point with an alligator clip. Only then power up the board and take the measurement.

Lesson Learned: When you’re soldering an SMD component which is so lightweight that you can’t touch it with the soldering iron without moving it, solder paste is your friend.
https://www.amazon.com/gp/product/B08KRB2J11
I’ve tried weighting the device down to the board using a toothpick clamped in a hemostat, where some of the weight of the hemostat is applied via the toothpick to the device. Clever, but I still move SMD capacitors, resistors, etc all too often. With solder paste you can apply the tiniest amount possible to one pad, then get the device positioned correctly, and touch your (smallest, sharpest) soldering iron tip to the pad, not touching the device at all. The solder paste flows and now the device has one pin soldered on. Yay!! The rest of the pads can be done with extra-fine wire solder. I’ve tried soldering the first pin by pre-tinning one pad using wire solder, but the resulting mound of solder makes positioning the SMD device much more difficult. I know some people hold the device with tweezers, flow the pre-tinned pad and position the device in the molten solder. I haven't had much luck with that. Solder paste is the winner, for me anyway.

Lesson Learned: The ATmega328p chips on those development boards are said to be clones. The second post on this topic
viewtopic.php?t=461 Broke my radio, part II
says the indication of a clone chip is a certain serial number which you'll see during the programming steps. I got that exact same serial number when replacing the chip on two truSDX boards, so it looks like I went to all that trouble, only to install clones. Whether that matters and will cause problems in our radios I cannot say, but I'd like to install genuine Microchip microcontrollers if I can.

Very luckily, on 6/27/2022 I found inventory at Mouser for ATmega328P-AUR and bought several of them at normal prices of $2.72 each. Mouser took my order and hopefully will be able to deliver the parts. They're hard to find; I started at
https://octopart.com/
and entered 'atmega328p-au' into the search box. I don't know what that 'R' designation means so I'm hoping these parts will be compatible with our radios.

Comments and better ideas are very welcome.

And THANK YOU to Manuel DL2MAN and Faraaz VK4JJ and all the others who help everybody here to build these little radios!

Rich AE8AA

[I have no financial interest in the products mentioned or Amazon.com. I paid retail.]

[G0UJA]

I also had to replace the microcontroller in my main board and for the removal I used the solder alloy method with a 25w Antex standard iron and it worked perfectly and was pretty easy to clean up with wick and flux afterwards.

The new chip was installed with ease using a low power iron similar to an Antex C15 with a fine tip.

[af7ux]

Since you had to buy a 3 pack of the dev boards, do you want to sell me one of the other 2? I was probing around and I believe I applied vin (c3) to the audio connector when I had a probe slip...

[TangoBravoMike]

@af7ux: Sorry for this slow reply; I don't come here often.

Thanks for the offer, but no. I've already used the second of three boards, harvesting another ATmega328 microcontroller for someone else's project.

Buying these development boards from Amazon is a good way to obtain the MCU chip quickly and at a reasonable price. They're hard to find and are selling for $8 to $10 each -- when you can find them.

UPDATE: See above; these are apparently clone chips.

[TangoBravoMike]

I've updated my story to say that the chips I found on development boards at Amazon are presumably clone chips, not the authentic Microchip ATmega328p.

Mouser currently has a small inventory of ATmega328p-aur parts which I'm hoping are compatible enough. It's hard to figure out what the subtype letters all mean.