Model Number: GU1500XTLQ1
This unit was completely inoperative and had stopped in the middle of a wash cycle leaving water in the tub. Knowing that power heads up to the board first, I went straight to the control panel to look for the problem.
Follow the Circuit
If we take a look at the circuit diagram for this machine (and excerpt is below) you will notice a thermal fuse (labeled TCO or Thermal Cut Out) that is connected directly to the 120vac L1 line. The fuse is in place to protect the control board in the event of excessive current load, or from excessive heat. A thermal fuse is used because a high current draw will generate heat so this fuse will respond to both over current or over heating conditions. A quick voltage check between the fuse terminals indicated 114vac (remember you will read source voltage across an open fuse) so this fuse has failed.
Why it Fails
In many cases, the fuse doesn't fail due to an actual problem, but more likely due to a loose terminal connector to the fuse. The loose connector will increase the resistance at the connection resulting in unnecessary heat being generated. And when the unit is in the middle of the main wash cycle with the pump and heating element operating, the current draw generates just enough heat to test the limits of the fuse. After the fuse is subjected to this heat one to many times, it finally opens up the circuit, and cuts power to the board.
Fixed with a Kit
Fortunately, Whirlpool has created a fuse kit designed to replace the original fuse and comes with a new set of connectors that when installed, provide a more secure electrical connection and reduce the possibility of further nuisance failures. It is important to replace the kit in it's entirety or you will most likely be doing it again some day soon. I installed the kit in this dishwasher and now it's back washing dishes again. When doing this repair, make sure and turn off the power to the unit before you touch the fuse or it will hurt.