Beogram 4002

12th February 2009

A Beogram 4002 (the later type with a DC motor for the turntable) would change speed from 33 to 45 RPM within the first minute of play of an LP record. The 33 RPM key could be used to set the speed back but it would not remain set for long before the problem recurred. These models use a relay to switch different resistors into the speed regulator circuit, the resistors include the panel controls and some extra trimmers inside. Measurements showed that the relay control circuit was unstable, before the speed change occurred rattling and screeching could be heard from the relay itself.

As well as changing the speed control resistors the relay is also used to control the lamps that illuminate the variable speed controls. The lamps also form part of the latch circuit that holds the relay in the correct position for the selected speed. In the case of this Beogram 4002 the indicator lamp for 33 RPM was open circuit, so as well as not lighting up the display this upset the operation of the latch by leaving the base of the relay control transistor almost “floating” and therefore susceptible to picking up noise. A replacement lamp cured the fault, the symptoms were considered to be unusual as whilst it is not uncommon for the lamps to fail normally this does not cause other problems. [Beogram 4002]