This is not really something you can do yourself (been there, tried that!). The machine has to be almost completely disassembled to get to the timing mechanism. Trust me, it's worth the 30.00 to have it timed.
I think http://www.allbrands.com
has a generic timing explaination for sewing machines (use the drop in bobbin one)...I found it easy to follow...but once I realized I had to unplug all the components for the computerized functions... I took it in to the dealer. If you contact Brother & your machine is under warranty, they will pay for the repair (they paid for my first two re-timings). Now I know you HAVE to use BOBBIN thread that is 60 WT only in the bobbin. You will continue to have problems if you don't. Also, this machine uses the class 15 bobbin, but make sure its model number SA156A, which is a hair taller than the SA156 bobbin..both are class 15, but the tiny difference is very important.