Decompile software to fix an old solar inverter

Decompile software to fix an old solar inverter

It is a fact that electronic devices become obsolete after a few years. Sometimes this is because technology has moved on, but it can also happen that a perfectly functional device becomes almost useless simply because the original manufacturer no longer supports it. When [Buy It Fix It] found a pair of used Power-One Aurora solar inverters, he ran into a problem for which he needed access to the service menu, which happened to be password protected. The original manufacturer had ceased to exist, and the current owner of the brand name was unable to help, so [Buy It Fix It] had to resort to reverse engineering to find the password.

Thanks to the Wayback Machine over at the Internet Archive, [Buy It Fix It] was able to download the PC software package that originally came with the converters. However, to access all functions a password was required which could only be obtained by registering the device with the manufacturer. It wasn’t going to happen, then [Buy It Fix It] started dnSpy, a decompiler and debugger for .NET programs. After some searching, he found the section that checked the password, and by simply copying that section into a new program, he was able to create his own key generator.

With the service password now available, [Buy It Fix It] managed to set the inverter to the correct voltage setting and connect it to his solar panels. Interestingly, the program code also had references to “PONG”, “Tetris” and “tiramisu” in various places; these turned out to be easter eggs in the code, containing simple versions of these two games as well as an image of the Italian dessert.

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Also inside the software archive was another program that allowed low-level functions to be programmed into the drive, things that few users would ever need to touch. This program was not written in .NET but in C or something similar, so it required the use of x32dbg to look at the machine code. Again, this program was password protected, but the master password was simply stored as the unencrypted string “91951” – the last five digits of the manufacturer’s old phone number.

The converter actually didn’t work when [Buy It Fix It] got it first, and his repair video (also embedded below) is also well worth watching if you’re into power electronics repair. Hacking solar inverters to enable more features is often possible, but of course it’s much easier if the entire design is open source.

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