You also need to remove the other threaded bits over the exposure control. I will try to take some pics of my disassembly, but I didnt take it far enough to get inside all the way, I was only interested in getting some electrical probes to confirm charging current.
I got to the point of removing the perspex cover. I was not able to take out the electronic part. I assume the dial at the back is holding the electronic module. Do you know how do take this apart?