Beocenter 7002

8th March 2010

With no loudspeakers connected and the volume control set to minimum the DC voltage at the loudspeaker output should be zero, if it is not the set will probably switch to standby when the loudspeakers are turned on. Assuming that the output stage components (3IC200, 3IC201, 3R226, 3R227) are not defective and 3TR205 (replaceable by a BF423) is not faulty the presence of DC at the amplifier output could be due to poor matching between 3TR201 and 3TR202 (both BC547C or BC550C), even though both may at first seem satisfactory in a simple measurement. Ideally a pair of matched transistors should be fitted as a replacement but if they cannot be obtained two from the same batch (e.g. taken from the same reel) normally yield workable results. The absence of the DC balance control makes the condition of the components in this part of the circuit critical. Numbers refer to the right channel, those on the left are numbered in the 100 series (e.g. 3IC100). [Beocenter 7002]