Without a schematic it's sort of tough from just a picture .
Semi educated guess .
The bottom right in your image appears to be PS.
It looks like 4 diodes with caps across them .
So I'd guess the 5 caps in that corner.
Looks like a voltage regulator in that area too.
Also wondering about perhaps a cold joint on a ground causing your hum .
Also a guess.
Really hard to tell just by a picture of the insides. I would need to see a schematic to say for sure. I doubt that changing the filter caps would solve the problem when and if you find out which ones they are. More than likely the filter caps are the large electrolytic caps I can see. Be sure all your gear is hooked up to the same wall outlet. If not you may have a ground loop problem. You could short out the inputs to see if the noise is internal or from an outside source.
Without a schematic it's sort of tough from just a picture .
Semi educated guess .
The bottom right in your image appears to be PS.
It looks like 4 diodes with caps across them .
So I'd guess the 5 caps in that corner.
Looks like a voltage regulator in that area too.
Also wondering about perhaps a cold joint on a ground causing your hum .
Also a guess.
I understand. Right now I searched for schematics of qinpu q2 but there is nothing available online.As technicians always say, working without a schematic is like working in the dark. Especially when the circuit is on boards. Point to point tube circuits are pretty easy to figure out but it always helps to have a schematic even with them.
Assuming that's AC power and a fuse holder looped around in that box? can't be good from hum standpoint... Try checking/cleaning input cables and jacks... Can't offer more without a schematic...
There's really only a handful all told. They're less than 50 cents a piece. You could change them all for a few bucks.
Pay careful attention to polarity.
Double,,triple check!
Just so we're clear I'm talking about round ones.
The green one's are films.
They should be ok.
Leave them be
Use a micrometers . Measure the diameter of ones you're changing.
Make notes of values (uf) and voltage rating
There is a simple way to test to see if it is a ground loop. You can get one of those cheap plugs that convert a 3 prong to 2 prong. That eliminates the ground to the equipment.
If the equipment is on a power bar or conditioner, you can use that 3-2 plug on that, and the equipment rack will be ungrounded. If you try that, and the hum goes away, then you need to figure out which components are contributing to the problem.
I am not recommending that the plug be the ultimate solution to your problem, or that you run your rack long term that way. It is a very cheap, fast way of eliminating ground loops as the source of the hum. Ground loops are very real, and often hard to resolve, even with 'good' equipment.
It might be a very sensible thing to try before you rip into your equipment. If it is a ground loop problem, it will likely still be there when you are done rebuilding your equipment.
Good point!
Is It possible to flip those wires to the outside edge as far from the board as possible.
You could also try a tube shield.
Assuming that's AC power and a fuse holder looped around in that box? can't be good from hum standpoint... Try checking/cleaning input cables and jacks... Can't offer more without a schematic...
Sorry for sounding like an idiot sir...! but what you mean by perfect is that i ticked the right caps on the image right?Perfect