Beocord 1700/2200

23rd May 2014

Capacitors 5C1 and 5C4 (both 10uF 16V tant) are inserted wrongly in these machines, correct operation of the headphone amplifier can only be obtained if it is the negative terminal of the capacitors which is connected to the bases of 5TR1 and 5TR2. Note that the circuit diagram is also drawn incorrectly in this respect. It is therefore wise to replace 5C1 and 5C4, fitting the replacements in the reverse direction, if 5TR1 and 5TR2 are found to be overheating and the DC voltages around them are incorrect. Electrolytic types can be used instead of tantalum if necessary.

Hum on both output channels can be due to AC field from the mains transformer being picked up by the power supply regulator. Adding a 10uF 50V capacitor between the base of 2TR23 and a local ground point (e.g. the cathode of 2D3) will eliminate this problem, a similar addition was made in the factory to later examples. [Beocord 1700, Beocord 2200]