My soap holder doesn't open during the wash cycle. i use the prewash side, but the cleaning is not as good.

i have the same issue

Check for the right amount of water in tub. In this unit close to the lip of the tub after fill. If water fill is correct check movement of lower spray arm. Other possibilities delayed action of dispenser from defective wax motor. Most probable is wash motor. Start unit after fill and when was starts, open door and see if water is being pushed to the top rack and dripping from the top of tub. Motor is easy to install.

Inside the soap holder there is a small spring and sometimes that comes under causing it not to open during the wash. If that is fine and you are using liquid soap try pulling a cople glasses of hot water on the latch and give it good clean because it soemtimes gets jammed up. Anymore questions give me a shout.

We went through the whole "clean the soap dispenser" deal and results were the same. Exploratory surgery revealed that the Prewash hose (for lack of better term), which connects from the top of the drum housing to the right side of the dispenser drawer (facing the machine)was completely clogged with gunk. Especially strange since we don't prewash hardly anything, ever. The hose that connects the bottom of the detergent dispenser with the side of the drum housing did have a lot of buildup, but I do not believe it was the cause because this was only happening on the rinse cycle. I also found the flow meter was frozen up.

These rely on mechanical timers and springs on the soap dispenser. They get a bit gunked up after a while. Don't prewash and run the the dishwasher for a few cycles with the dispenser open (put the soap tablet in the cutlery basket). If you listen to the machine you may be able to hear the click when the dispenser should open which at least tells you that it should be working

remove the door panel and replace the wax motor on the dispencer

its either the dispenser or the timer/pcb.

According to my information the dispenser drawer has four separate compartments for adding laundry products to the wash load. These compartments are:
1. Prewash Detergent Compartment
2. Main Wash Detergent Compartment
3. Bleach Compartment
4. Fabric Softener Compartment

Laundry products are diluted and dispensed automatically
at the proper time during the wash cycle. The separator in the Prewash and Main Wash Detergent Compartment can be moved to accommodate either liquid or powdered detergents.

water is getting past the gasket during the start up cycle. by the time the door opens, the water has caked up the soap. also, its not clear when in the cycle the door is opening.
try using liquid soap.
also, take a peek just after the machine has finished filling and starts washing to see if the door is opened on the soap disp.
good luck
mark

Something simple you can check is to make sure the spring that flips open the door is not broken or caked up with detergent.

As for the soap not dissolving, I've had similar problems and the only solution I've found is to make sure you are not blocking  the spray jet on the bottom from hitting the soap drawer.