The digitizer (touch screen) on my WiFi iPad 1 would sometimes stop responding on the lower 1/3 of the screen.
After looking around the internet, it appeared that the problem lay in how the digitizer cable and main board connect. The clip that secures the cable was intermittently coming loose. Other sites mentioned the use of mylar tape to secure the ribbon cable, so I purchased some from eBay. I used a 1/2" wide x (approx) 1.5" long strip of tape to hold the ribbon in place, securing it to the cable, clip, and main board together. I also used a smaller piece of mylar tape to secure the cable for the headphone jack, as it has the same design issue.
Siince I had already opened up this unit before, I knew what to expect, so I prepurchased a set of display clips from ifixit.com
This repair was fairly easy to do, especially since I already had the Pro Toolkit and the display clips. If you are a DIY-kinda person like me, the Pro Toolkit will find a use all over your home and with your devices. It is well worth the upgrade over the basic toolkit.