Hi and welcome to Beoworld !
Generally, three issues count for the vast majority of faults in these decks;
1. Cracked solders from millions of micro-vibrations from the mechanics, especially in the power supply and rectifier areas and at the connectors along the edge of the main board. Resolder the lot.
2. Aging capacitors. They dry out with age. A convenient kit is available for this.
3. Tachodisc pattern disintegrates. New tachodisc is available.
Your Beogram will have 1 and 2.
Check 3 while in there. Replace the tachodisc with a new stainles steel one if yours is of the photographic type.
Other things to check; The muting relay and the connections to the DIN/relay board, depending on the type of relay it can have oxidated contacts so the muting fails (you will hear the needle land on the record etc.). Cleaning and relubricating of the servo motor threaded shaft. Check the servo motor belt for slippage (new belts are available), replace if it's still the original triangular type.
Martin