[wkand]

You do need the schematic, but while you are waiting...

The waviness suggests electrolytic filter caps in the power supply, but depending on where in the circuit the melty squarish cap is located, if it is a bypass cap to ground, you could get minor ripple in the picture like you are describing.

Change that cap that is getting hot or melting, but if you can, check voltages first on either side of the cap that is melting. It does not matter what the values are supposed to be for this test, so long at they are not identical or nearly so. That would indicate DC leakage. Also, remove the cap and check voltages after it is removed if you find that the voltages are the same with the cap in circuit. if they change after removing it, that is more confirmation that the cap is leaking.

the other thing to check for is a major difference in the DC voltage on either side of this cap. if, say the working voltage of the cap is 100 volts DC, and you measure a 250 volt difference between the two leads of the cap, that's a problem you need to check out, else the new cap will end up doing the same thing.

Replacing it is a matter of carefully reading any markings on it and deciphering them using the web or this group.