Cambridge 640P Pre Amplifier Repair

Fault
Unit powering up, but no Audio output.

Internal inspection of the power supply section confirmed that C3 330uF 35V smoothing capacitor had vented and there was also corrosive damage to R42 150 ohm resistor.

Cambridge Audio use a glue during manufacture to provide additional support to larger electronic components.

The problem is the glue becomes highly corrosive over time.

The video shows the power supply section and the brown glue covering large parts of it.

R43, R42 150 Ohm 1/4 Watt removed
C5 &C3 330uF 35 V removed
C4 & C2 1000uF 35 V removed

The brown glue was removed and the board cleaned to remove any trace of Electrolyte.

New components and the plus and minus 18 Volt supply rails checked.
All good and the output relay could be heard to change over.

The MC/MM switch and the Filter switch on the rear were cleaned with De-Oxit as well as the input and output RCA sockets.

Unit fully tested , working correctly.