Beomaster 5500

20th October 2008

This receiver would switch itself off a second or so after being switched on. The usual cause of this is an excessive DC potential at the loudspeaker outputs so and further tests must be made with the loudspeakers disconnected. In this case -37V was found at the midpoint of the two right hand channel output transistors, normally the voltage should be zero, give or take a millivolt or two. In all B&O amplifiers that use a BF423 transistor this is the first thing to check and sure enough TR205 showed considerable leakage when tested with a meter. A replacement failed to cure the fault however. TR206 (BC547B) read strangely in circuit so this was replaced too but this also made no difference. The true culprit was C215 (220nF / 63V film type) which was leaky. This capacitor is not shown on all issues of the circuit diagram, making tracking down the fault more difficult than it could have been. [Beomaster 5500]