The dishwasher detergent door opens during cycle but powdered soap remains in tray. At end of cycle glasses and dishes are wet. a little water is left undrained at bottom. This is a Frigidaire model FDB510LCS1. Checked upper and lower spray arms and they seem ok and pump seems to be working
I have seen this problem before on a couple of dishwashers.
How are the dishes doing? Are they coming out clean, or do some of them "fail".
If you rinse the dishes before putting them in the dishwasher, it may be hard to detect "failure" to clean. Try not rinsing the dishes once and run them through a cycle. My guess is that the "failure" rate will be high.
The problem I have seen is that the dishwasher water input filter is either clogged or the water-full sensor is "telling" the unit that there is enough water in before it actually fills properly.
So, some water can get in, but not enough to properly wash the dishes and dissolve the soap.
On the appliance repair sites they have parts breakdown details and what you are looking for is an input valve assembly -- the point just after the water line connects to the dishwasher.
Now the valve may be OK, but the feedback system could be bad.
(On a Bosch dishwasher the valve IS the feedback system and the filter.)
Any filtering or "water full" signal will feed back to that valve.
If you get inside that front lower panel, be sure to turn the electricity off first 'cause if you get crosswise in that area you could end up with a 'shocking' experience!