Back is the hardest of all the muscle groups to isolate and work properly without biceps/forearms bearing the majority of the workload.
A few tips on training back to keep the stress on the targeted area:
1. Use a false grip whenever possible (thumbs over) while doing chins and rows. This will keep you from using too much arm power. Also, this is much easier if you use straps which leads me to my second point...
2. Use straps! If you need grip strength and foremarm development, then do wrist curls some other time. You are here to obliterate your back so keep that as priority. 9 times out of 10, someone's grip strength will fail before their back fatigues when doing shrugs, seated rows, T-Bars, DB rows, chins, and even pulldowns. Let the straps do the "gripping."
3. Banana back! A slight curvature (concave) to your lower back will keep the stress in your lats and traps when doing rowing motions. DO NOT ALLOW YOUR BACK TO HUNCH OVER!!! This puts unnecessary strain on the lower back, invites serious injury, and negates much of these exercises' effectiveness.
4. Visualize and mentally connect with your back. Concentration is key when doing back or your missing the point. You've got to feel you lats working...just arbitrarily rowing and pulling without regard to form is totally pointless. When doing chins, imagine "pushing your elbows down" instead of "pulling yourself up." I heard this phrase a long time a go and never forgot it. It has helped me tremendously.
5. It takes practice. I don't know how long you've been training but it takes a while to get back training down just right so that you're really targeting what you want to. Practice getting in the right goove so that you maximize the stress on your back. The reason back is so hard to train is because almost every exercise designed to train it is a compound one. Therefore, ancillary muscle work (i.e. bi's, forearms, rear delts) must be minimized. In truth, I have seen very few people who train back properly due to the aforementioned reasons. I've seen people who have been training for years that still have trouble isolating it just right.
Hope some of these suggestions help.
Good luck.