Question: How do I graph a solution curve in the phase plane for an OED?

I am dealing with second order linear differeantial equations for RLC and forced RLC circiuts.

I am having trouble with plotting a solution curve in the phase plane.

> restart;

with(plots); with(DEtools);

L := 10; R := 20; C := 1/100;

de1 := diff(x(t), t) = y(t);

de2 := L*(diff(y(t), t))+R*y(t)+x(t)/C = 0;

DEplot({de1, de2}, [x(t), y(t)], t = 0 .. 5, [[x(0) = 10, y(0) = 0]], stepsize = 0.5,

color = black, linecolor = blue)

This works wonderfully and gives me a nice spiral in the phase plane.

When I try to graph for the following two set ups it get ugly graphs with no arrows for the phase plane.

restart;

with(plots);

with(DEtools);

L := 10; R := 20; C := 1/100;

de1 := diff(x(t), t) = y(t);

de2 := L*(diff(y(t), t))+R*y(t)+x(t)/C = 200*sin(t);

DEplot({de1, de2}, [x(t), y(t)], t = 0 .. 5, [[x(0) = 10, y(0) = 0]], stepsize = 0.5,

color = black, linecolor = blue)

And

restart;

with(plots); with(DEtools);

L := 5; R := 8; C := 3/100;

de1 := diff(x(t), t) = y(t);

de2 := L*(diff(y(t), t))+R*y(t)+x(t)/C = 800*exp(-0.5e*t)*cos(8*t)

DEplot({de1, de2}, [x(t), y(t)], t = 0 .. 5, [[x(0) = 3, y(0) = 0]], stepsize = 0.5,

color = black, linecolor = blue);

I have been tweaking the values for t, but I can't get a graph that looks good.

Could anyone tell me where I'm going wrong?