Beogram 5500 the tonearm isn’t moving forward.

[gpv]

My Beogram 5500 has an issue.
After I fixed the tonearm—which used to get stuck halfway across—a new problem has emerged: when a record starts playing, the tonearm tracking doesn’t work; it stays in place, causing the stylus to remain in the same groove and skip.
Essentially, the tonearm isn’t moving forward.
What checks should I perform?
Where are the sensor and the light bulb for the tracking circuit located?

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