Automower 450X lightning damage repairs
I’ve been using Husqvarna’s line of Automowers for about six years now. They’re fantastic, versatile, reliable, over-engineered works of Swedish ingenuity. My first was a 315 that I used to maintain myself with a gray-market DVD of their dealer-only Autocheck EXP and a lucky guess of “guest / guest” for dealer login. Added a “Connect” kit and even a wifi connection to it. Upgraded some years later to a 450X, but by this time, Husqvarna had locked out the hobbyist market with Autocheck 3 which had actual security measures to keep unauthorized folks out. So much for any right to repair on these things.
In July of 2022, a serious thunderstorm passed over, and lightning struck the small pond behind my house while the mower was docked. I don’t know if the surge came up through the boundary wire or through the house AC wiring. Either way, the result was a base station with a solid green light, whether the boundary wire is connected or not–the definitive sign of a fried base station board.
No worries! These boards are semi-universal, and I had a spare from a lot of troubleshooting with a 435X before finally going back to the 450X. Replacing the base station board and regenerating the loop signal, everything seemed good.
Or so I thought.
The behavior I saw with it was this: It would back out of the base station, but rather than stop, it would just continue backing out for several yards, before stopping and giving this “Stuck in charging station” message. Somehow, it was never getting the signal that it had left the station and was continually trying to pull itself out of the station without realizing it was clear of it. The lightning had clearly blown something up in the mower itself. Bummer.
I did the tango with my insurance company, and after paying a hefty deductible, I purchased a new 435X now that they’d worked all the issues out of it. The insurance company let me keep the old one, which I had planned to sell for parts or keep for some kind of robotics project at some point.
Cut to Easter Sunday 2023. I’ve been messing around more with electronic components, working on Ben Eater’s 8-bit breadboard CPU project, and generally getting more comfortable in my understanding of how electronics work, at a very basic sort of non-academic tinkerer level. I started thinking I might try to get the 450X working again just by poking around on the main board and trying to suss out what got fried.
I started by tracing where the base station blades connected to the motherboard, and immediately found that the positive blade ran into the drain of this MOSFET (the one right in the middle with all the glare).
I noticed the gate and source were both connected together before heading into the rest of the circuit. Could they be using this MOSFET to tell the logic if the mower is docked or not?
Automower boards get covered in some kind of water-resistant epoxy for good reason. Scraping off this coating, I looked up the part number (Infineon IPD50P04P413ATMA2) and found that it’s a 40-V, 50-A P-type MOSFET. There are a few others on the board. I’m not a professional electronics dude, but I know that they should all behave the same when probed. I got a little resistance from drain to gate/source on the others (after scraping the gunk off to make connections), but the one connected to the base station blades was just shorted straight through. Ah ha! Could it be this is what was causing it to think it was still in the base station? Could I just pop this thing off and it’ll just work? Having nothing to lose, I pulled out my knockoff Hakko hot air rework station and removed it.
And here was the result:
I cannot believe that actually worked.
Okay! But let’s not leave it like that since the next thunderstorm might take out something more important that would be a real struggle to replace. I could have just ordered a replacement board for $$$, but it would still have taken an authorized Automower dealer to reprogram it, and there isn’t one within hundreds of miles of my place in rural Virginia. So instead, I found a suitable replacement at DigiKey.
After replacing it with the world’s worst soldering job, the mower continues to run great. A $3 fix for a $3300 mower! Already having a working 435X, I gifted this one to my step-father rather than sell it. When the universe surprises you with something like this, it doesn’t hurt to pay it forward.