Last month a customer presented a nicely preserved Musical Fidelity Elektra E100 integrated amplifier for repair - the fault was that there was considerable mains hum audible from the loudspeakers on all inputs.
Further investigation in the workshop showed that the mains reservoir capacitors on the main circuit board which feed the power amplifiers were bulging and well past their sell by date. These were replaced fairly easily with modern equivalents which were physically much more compact than the originals.
Here is a pic of the main amplifier printed circuit board to allow the removal and replacement of the main power supply capacitors.
Here are the bulging resevoir capacitors that have seen far toom much action. Now that the main PCB is removed, we can easily change these four tired electrolytic capacitors for modern equivalents, which are incidently quite a bit more compact.
This is the reverse side of the main power amp PCB, ahowing star earthing technique and overheated parts of the PCB.
The pre-amp power supply capacitors at 220uF/ 35V were also found to be dried out and bulging and these were also replaced. The repair was effective and all mains hum removed, hopefully this Musical Fidelity amplifier will continue on for another 15 years good service without issue. Here is a link to a pdf file of the schematic circuit diagram for the Musical Fidelity E100 amplifier.
