All,
at first kudos to @KaFr and @ways_ahead for the 24/7 support via messengers.
Time for a little update on my revival project.
I am member of a german forum
www.GoingElectric.de since almost 10 years. This forum is car-centric but also has a motorcycle section. For my local area there is a forum meeting organized in a cosy little cafe on the outskirts of a smaller city every four weeks - an ideal place to present my charger issues and have the experts look at that thing and come up with suggestions.
Unfortunately, the findings did not really lead to a solution but maybe it might be of interest for you what the experts were concluding on:
I brought the charger electronics for visual inspection and also a Fluke multimeter in case something should me measured. Actually, the inspection showed that there is no suspicious part. Everything at least
looks like it should work perfectly.
I also brought a larger printout of the wire diagram which we analyzed.
When the charger is connected to AC, the signal AC_sense is on high level. This signal goes into the VCU in connector C-01 Pin 15 as
U2C Charger_AC_SENS. We believe (!!no fact, assumption!!) that the VCU has the task to check if charging conditions are valid. Could be done like temperature conditions, undervoltage. See my initial post where I mentioned the dashboard shows
severe undervoltage. It looks like then the VCU signals back to the charger a signal on C1 (VCU connector C-01 Pin 27) - probably HIGH. The charger may start charging. There is also a direct signal between VCU and the Batterie RS485 bus: Pin 26
Charger enable. However I have not yet found a method to tap into that signal to see if it is there or not. But I can perfectly measure the connector C-04 on the disassembled charger.
This is what I have observed (it took me a while to figure out how BBCode works

):
Pin C-04 | Key-Off | Key-On | Charging |
1 - NC | . | . | . |
2 - FanPWR_Out | +1.15V | +1.1V | +1.15V |
3 - FanPWR_in | GND | +12V | +12.5V |
4 - AC_SENSE | +1.44V | +1.45V | +9.4V |
5 - WARNING | +1.5V | +1.5V | +1.5V |
6 - NC | . | . | . |
7 - BATT - | . | closed | . |
8 - NC | . | . | . |
9 - C2 | open | open | +0.6V |
10 - FAULT | +1.5V | +1.5V | +1.5V |
11 - C1 | open | open | +0.6V |
12 - NC | . | . | . |
Ladies & Gentlemen, now its your turn. Please help me! What are the proposed next steps here?