In the first models (ST1 / V1 / V1.1), the power electronics in Stromer bikes for motor support control were housed in the motor. Due to various problems (temperature, water, moisture and thus corrosion), it was first encapsulated and finally packed in a separate module, the controller or MCU (Motor Control Unit) under the down tube or in it (ST2-Belt, ST7).
Control defects are quite common. As the assembly has been cast in epoxy resin since around 2018, it is virtually impossible to repair.
Defects are often, but not always, visible. If MOSFETs "explode", measurement is pointless, the damage is visually obvious.
Even a defect in the charging section does not require further forensics.
For error E210012 & 210109, Stromer provides instructions on what to check visually before inserting a new battery. However, this is only possible for MCUs with a transparent seal.
If there are no visible problems, it will be difficult to diagnose the fault. However, an electrically simple test of the MOSFETs (if not visually visible) is possible. I link here to a document from the company 'GRIN Technologies' (ebikes.ca) "Testing for blown mosfets"which illustrates the procedure with a multimeter very simply.
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