I had an issue with the power antenna not moving (it's a new mast), which I traced to the headunit supplying a constant 12V to the antenna circuit at all times. I got the antenna retracted and then disconnected the plug.
Around this time, I also had an issue with parasitic battery drain starting around the same time.
These symptoms to me suggested something along the lines of a power transistor inside the headunit failing in a low impedance state. I opened the HU up to investigate and sure enough we see scorched components.
I'm not going to try and repair it, these SMD components are too small-scale for my soldering equipment. If anyone would like to have a go, you can have the headunit for free. I think I'm going to chalk this one up to buying the cheapest headunit on AliExpress and receiving the cheapest headunit on AliExpress.


M07 according to datasheets is a power diode, and 3407A is a MOSFET.
Either way they have obviously seen too much current. It's possible they are simply undersize for the current draw of the S40's antenna mast control input.