Monitor Speakers repair

  This pair of active monitor speakers just came in. The speakers are the Alp5 set made by Event electronics. One of these speakers was making weird hum noises which led me to a single conclusion: filter capacitors... The electrolytic capacitors(caps) used in their amplifier section to filter out the power supply hum and the EMI (electromagnetic interference), get old and their capacity could be dramatically reduced over time.
 This was the case with this monitor speaker and I decided to change most of the electrolytic caps on its built-in amplifier pcb. The dual amplifier  LM3886 ("gainclone") circuit of the ALP5 is a very nice unit with two large 4700uF/50V filter caps that had to be changed.
 After soldering a new set of psu caps in, I also changed two smaller caps rated at about 10uF to ensure no noise and psu hum is audible. When I finished working on the speaker, there was no hum and noise except a normal hiss at ultra high level settings and no music playing through. Now the speaker's got a really high SNR (signal to noise ratio)!

Here are a few pictures taken during the repair:

 

 

The back side were the audio amplifier connections are

 

Inside the speaker: the psu and amplifier board

The woofer and tweeter units

 

The dual LM3886 IC audio amplifiers and their heat sink:

Both monitor speakers opened for inspection

 

The old 4700uF capacitors

The new capacitors are in!

The new caps are a bit larger than the old ones!