Beocord 9000

9th December 2008

This recorder (an early model with the complex Dolby PCB) played back OK but its recordings were spoiled by a faint but regular clicking sound on one channel, between one and two clicks per second was typical. An earthing fault was suspected and upon investigation the earthing arrangements for the deck were found to be odd indeed. The motor can was earthed through the supply cables (returning via P1/12) but the earthed side of the motor supply filter was returned to the deck itself. The only deck earth was via a tag on the combination record / replay head, this was returned to P19/6. P19 is also the connector for the replay head, so the deck earth effectively channeled any surplus charge into the sensitive amplifier circuitry.

The lead between P19/6 and the head was removed, the deck was then earthed by fitting an eyelet tag under one of the three mounting screws and soldering a wire between this and the screened cover of the microphone amplifer. This arrangement removed the clicks completely. It was thought that the capstan belt was becomming statically charged and that the poorly designed earthing arrangement was allowing the resulting dischages to be recorded onto the tape. [Beocord 9000]