Of course it would be helpful if we knew the cause affect of Wooo back problem(s); muscle, spine, joint, nerve damage, etc. Lower, middle or upper back? And does overhead pressing cause back pain? But anyway I'm going with the idea that's it's the lower back causing trouble.
Might consider chins as opposed to pulldowns. With chins you are moving a body through space. Allowing, for the most part, less stress on the lower back. With pulldowns you are forced to anchor down the lower body. That pivot point on the lower back is receiving unneeded stress. Even those bench/incline rows (pictured) can affect the lower back of some people by the simple act of holding the body/back in a firm position (like in the DL where the back is holding the body in position while the legs are doing the actual lifting from the floor). For the time being you might want to avoid any form of bent over rowing until the back is normal.
Another benefit of chins is that they can help stretch the whole back, helping with a natural alinement. Rope climbing ( leg straight out) is an excellent back (and bicep) exercise, though few men have the opportunity to do this exercise. Chins are a mass builder when done right, with experimenting with different hand spacings. And adding weight when ever possible.
Pullovers are also a excellent back exercise, with less stress on the lower back when the knees are drawn up during the movement. This position also give a better stretch to the lats/back/rib box because the ab's are more relaxed (less pull from them) than when the legs are stretched out. GM'ing are also good, but just use the bar for higher reps to start with. Probably a couple sets of 50's. May seem like sissy stuff, bar only, but you want to bring more flexability and more healing blood to the lower back area. In fact I would doubt that not too many men who come to this site could do a 100 rep set of GM'ing without stopping. But do add weight as the lower back becomes stronger.
Might try chins follower by pullovers (bent or straight armed). Or a set of pullovers before chins. Pullovers are one of my favorite exercises and have gotten some good results with a set of straight are pullovers (lighter weight..7-10 reps) immediately followed by a set of bent arm pullovers (heavier weight...7-10 reps). Either BB or DB's with pullovers. DB's seem to give me a better stretch. Good Luck.
Side Bar: if the injury lingers, staying about the same, than rest would be advised. That and seeing a sports doctor.
