Parasound HCA 2205AT - Modications / Upgrades

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Yes indeed some of the 15,000uF power caps are a bit sweaty so I was planning to replace all 10 of them (though by itself this couldn't be causing the standby issue). I've got my sights on some Elna caps (100v instead of 80, 105C instead of 85) in China (just hope they are actually Elna's).
1pc ELNA 100V 15000UF Capacitor 4-Pin 35*80mm #J2445 | eBay

Now I'm on it I am looking as possibly upgrading some caps in the signal path due to its age. Do you have some experience with this? I heard some change a bunch of small yellow parallel caps but they don't seem to be in the signal path but rather power supply.
 
So I've measured all 5 amps before the relay. Once the amp was stabilized they all measured around 0.5-2mV DC. Some started at +100mV DC, another started at -100mV DC, but they all end around 0.5-2mV DC.

Next step is to check the control circuit. Visually it looks to be ok ..
 
Although everything is working fine there is still one thing left and hope you guys can help to find a solution.


When the amp is switched on there is an annoying hum, we think it is originating from the giant transformer but don't know what to do to tackle/let the hum stop.



Can you help?
 
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