Quoted from RobbyIRL5:
YIHUA 939D+ Digital Soldering Station, 75W Equivalent with Precision Heat Control (392°F to 896°F) and Built-in Transformer. ESD Safe, Lead Free with °C/°F display + 5 Solder Tips, Solder & 3 Extras amazon.com link »
Looks like I got the Amazon special LOL. Which I promise was much better than what I had in my toolkit from years ago!
Digital control is important, so you have that, which is good, even if it's mysteriously-named YIHUA powered. You want to use the fine tips only.
What solder are you using? You want fine electronics (thin gauge), rosin core solder which has the flux built into the center of the solder. Flux is the magic that facilitates the smooth flow/melding of the solder. You can buy it separately, but by using rosin core solder in the first place that's not usually necessary. I use 60-40 rosin core solder because it works better than the awful all tin stuff - just puff little "candle blowing" breaths out as you're soldering to keep the smoke away from your eyes and nose.
Once you have the right solder, the temp is very important. You want to only need the tip on the target for a short period of time. I do most of my soldering at 650F. Some people recommend lower at like 600-615F, but I've found that for me 650F works well and doesn't have me holding the iron on the target too long, which can raise pads or traces and kick off a bad day.
There are a bunch of soldering tip videos on youtube, but this one's pretty good for beginners:
A good soldering station and a good multimeter (Fluke 107 for ~$105, or better, Fluke 117 for ~$200) are the two best things you can buy for a new pinball machine. If you don't have those, forget mods and save up to get those FIRST. If you're going to be in pinball for any length of time, you will need them.