I'm coming into soldering PCB work with nearly zero experience. After contacting a couple console repair shops in the area, getting no responses, I decided to get the tools myself. Videos made it look like a simple process. I made a mistake, and hoping the community here can help. (I don't know how I missed the existence of this site before. I would have asked for help here first.)
Hiya! Welcome to the forums. I'm sure if I'm saying anything wrong I will be corrected by the other techs. Glad you posted detailed photos to make the process smoother on all of us.
1) My obvious mistake: C122 in the lower right of the picture. While trying to remove an old cap leg I accidentally pushed it a little too much too early, and the entire pad came off the board. I nearly lost it. Thought of putting the pad threads through hole and soldering it there (small bit of solder primes below it), but realized I had no idea what I was doing and stopped. Looking for advice on where to attach the negative leg of the new cap.
Ok, so you lifted the pad. I've done this quite a few times, but like anything practice will make this easier the second time and you will be more careful and more aware of the pressure you're putting on the board and the heat of your iron.
Look on the bottom of C122, right below where you lifted the pad. See how there is a hole right there? That's called a "via". Its where the electrical signal passes through. You can either solder a cap leg into that hole (it will fit), or scrape a bit right below the hole with an X-Acto knife to reveal the copper trace. solder your other cap leg directly to that trace. I know. It's tiny, but it looks as if there is a little solder blob currently covering part of it. If you clean it with a copper braid you should be able to reveal a bit more of the trace. I would personally just solder directly into the hole if the copper is still visible there. Or, its a ground, so anywhere you can find a ground.
2) The negative pad on C102 looks deteriorated, but still attached. As long as it's attached, it should be good to solder too, right? How can I test this?
Yes. just be careful. It's definitely a little krinkled. You can test this with a multimeter or test light with the system powered on. If you end up lifting the pad, follow where the copper trace goes (usually connected to one corner of the pad), and again scrape away a bit of the green with your knife to reveal the copper trace, and solder to that. There also may be another via (hole) close to the pad you lift, in which case you can repeat the above process and solder to the via.
3) The negative pad on C322 was completely corroded away, and came right off as I cleaned off the old solder. Again, where should I attach the negative leg of the new cap?
See the hole directly to the right of C322? there is a little trail from the neg. pad right to it? The first hole, on the right perimeter of the box right next to the white line, at 3:00. Solder the cap leg into that via.
4) C612 had a lot of corrosion under the cap, but the pads still look good. I'm worried that the corrosion may have damaged the board. Looking for an experienced opinion on that area, and how to test the lead.
Clean it with a q-tip and alcohol, directly below where the cap was. My bet is that you will reveal a lot of copper once the electrolytic fluid and flux are cleaned up. Solder directly to the pads and test. If the pad is still there use that, otherwise if the pads are lifted:
The positive side will go to the via, a hole right below the (+) on the left of the pad.
The negative side will go pretty much anywhere on that thick copper trace right below the pad (you can follow it all the way to the left if you need to). Try to orient it as close to the pad as possible so you don't get confused. After you clean the board it will make more sense. I don't think its as bad as you think.
5) C306 was difficult to remove, and it seems that the metal surrounding the hole on the negative side may have been compromised (pulled away from the board?). How can I test that the connection is still good?
It looks fine. that area that looks narfed is a ground (negative), so just try and install after you clean it up good with alcohol. Unless I'm mistaken the positive on that cap is at 12:00 (top).
I haven't added new solder to any of the pads as I knew I wasn't ready to put all the new caps on yet. Hoping to get the console in working condition soon.
Just go slow and be careful when you reinstall. If you feel yourself getting pissed dont force it. Unplug the iron for a minute, have a coffee and take a 5 minute walk and then come back to it. You don't want to get caught in a gumption trap.
You're almost there! Good luck!