I have a concern about cracks on this bike. I got the frame on CL about 3 months ago. It's a '88 Schwinn fixed conversion. The previous owner welded track ends on it and pulled shifter bosses etc off. He seemed like he knew his stuff and didn't just have welding as a hobby. It was painted when I got it and had a few nicks.
I built it up and have ridden it about 200 miles.

I noticed some cracks where the brake bridge meets the seat stays. I don't know if it's just the paint or the frame under the paint. Besides sanding off the paint to see for myself or taking it to someone that knows a lot more than I do, what can anyone tell me.
The bike rides fine but sometimes I think the front wheel does not look like it's going straight when I ride with no hands, like the rear of the tire might be off to the side a bit.

Also it looks like the brake bridge might be a bit higher on the non drive side. Maybe it was built that way since some things are not symmetrical.

its look like cracks in the paint. you might want to sand one to get a closer look. Does the wheel move like cones are loose ? if so yes the frame may be crack, the good news is it can be fix by a welder,and repainted.