I plugged it in after opening it up in the hope to see the location of the smoke should any develop...;-). No smoke, but no tracking either. Pretty much nothing worked, no tone arm lowering etc...also some traces of amateur repairs.
I determined that the light bulb in the tracking sensor was out, and I decided to replace it with an LED since the bulb cannot easily be replaced since it is glued into the sensor housing, i.e. cannot be separated. I also am a fan of LEDs since they have a much better long-term stability, especially should the unit be shipped at some point.
On to the dead sensor arm!