Top rack wont clean - LG LDF6810 Built-in Dishwasher

Possible that the main pump for the spraying system is not working, you will need to check the INLET valve , remove and check if there is flow when the washer is switched to start, if not the inlet valve is faulty as it does not allow water to the pump.
check this link for tips to check the pump;
http://www.espares.co.uk/advice/dishwashers/a/3/1293/how-to-replace-the-spraying-system-on-a-dishw.html

Check that the top rotating arm jets are not block. These often get blocked by pieces of food or other solid particles, this is the normal problem.

the top spray arms would be clogged for the top rack not to be cleaning but now it sounds like the main pcb/computer has sizzled and needs to be replaced

Your filter/chopper is clogged. You have to clean it out and that will restore water pressure to the top rack.

1. Remove the bottom rack.
2. Remove the top rack
3. Remove bottom Spray arm (turn top nut clock wise)
4. Take off the delivery tube by turning it clock wise over the heating element ( undo the two clips one at the back and one on top)
5. Take out the screw for the top screen and remove top
6. Take one screw out for chopper housing and remove
7. Remove chopper and clean or replace chopper if broken

Reinstall all parts and test.
That should help please rate your experience. Thanks

IF you take the racks out and look at the back you will see a tube that runs from the pump to the upper rack spray bar. The tube has TWO connections that the upperspray bar contacts but it only uses one of them. The other is closed off by a interior flap. If the flap comes loose, it wont allow enough pressure to the top spray bar. If the pump is plugged it wont build pressure either.

Check whether the top rack spray arm main hose sits firmly into the
machine. If there is a leak in this area water pressure may not develop.
Also check the water pump in the machine!

See pictures of how to fix this at:
http://forum.appliancepartspros.com/dishwasher-repair/8174-kitchen-aid-dishwasher-wont-clean-top-rack-items.html#post129837

likely not .....the problem may be how you stack the dishes ....try doing a load with nothing on the bottom rack ....if the top rack items come clean then you may be stoping the water from reaching the top rack with the dishes on the bottom rack ....it's important to keep the center of the bottom rack free this is where the water comes from (on most models). to clean your upper rack .....have a close look at the inside of the machine to try and figure out where the water comes from ...it helps a lot to understand this ....good luck

You'll need to clean the food chopper in the base. Make sure you've got a torx screwdriver.

http://forum.appliancepartspros.com/dishwasher-repair/8174-kitchen-aid-dishwasher-wont-clean-top-rack-items.html

This is one common possibility
It may be the food chopper assembly. Mine broke last year from a toothpick,
the food doesn't get chopped because the blades are broken, then the filter clogs and water wont spray high enough.
Heres a test--turn on the dishwasher and wait until you can hear water running then open the door really fast and look at how high the water is spraying--there should be alot of water all over the top rack running down