I didn't replace my thermo/hygro chip yet, and I don't need to right now because I fixed the issue of the humidity not going past 93% at night. What I did was take a soldering iron, and heated the 4 wire ribbon cable on the very top board when you take the black cover off. It says on the board "test" I believe on the 4th connection. You may have other issues with the wire, but I would start there. Inspect the connections for poor connections and heat up the end of the wires and solder them over if needed. The wires are very frail and mine were so brittle that they broke away some.
You can get a solder iron cheap at harbor freight, and it has a nice tip to it. You want a small pointed tip. It can take some practice to solder like a pro...
Nincehelser recommended cutting off the white push down on these replacement sensors and soldering them...