Onkyo M-505 Recap Project

20 seconds is too log, on the size of soldering pads like the ones in that amplifier I usually count 1-2-OUT in my head (making less than 3 seconds).
Also with 12 EUR irons...

What made you work so long and why multiple attempts on the joint?
You need to solve this problem before continuing (either on this amplifier or any other equipment) - tehse amps are "the easy ones" from soldering point of view 😉
 
tehse amps are "the easy ones" from soldering point of view 😉

I have been soldering for 50 years. This is the hardest to service amplifier that I have ever encountered.

If I decide to service it again, I will be completely disassembling it.

But for now I will be purchasing a BGW, which is actually designed to be serviced (unlike the amp in question), with the proper soldering station.
 
20W seems to be not enough.
Before buying a "weller" I used Vellemann TVTSS6 30/60W iron for years. Once you get used to it and do not leave it idle at 60W for long I do not see it as a "problem". 30W I used for resistor leads etc, 60W worked with larger planes (but with very large areas it was not cearly enough).
Also the soldering tip cannot be too sharp in cases when the soldering pads are larger rather than small.
 
I decided that I am going to purchase a station that I can precisely control the temperature to the tip.

I have been successfully using such stations since the '70's.

The modern ones appear to be unreliable, so I am looking at vintage models. My main concern is finding readily available tips and heating elements for them.
 
My main concern is finding readily available tips and heating elements for them.
Heaploads of tips and probably elements are available "anywhere" - starting from eBay/Aliexpress and ending with Mouser.
The practical problem is that the unbranded "Hakko" (just as an example) tips may be ca 0,5 mm too short or too long and you have to start mechanical adjustments. So my advice is to buy only branded/original tips ignoring the fact that others are way cheaper.