MOSFET switch won't switch

Actually, now I think I may have been incorrect above about a depletion mode FET inherently sitting in the linear region.  I found a couple of useful discussions of the topic that make me think they in fact are inherently in the saturation region with zero gate to source voltage (though neither explicitly states that fact, just seems to imply it).  I'm not positive about this anymore, my uncertainty comes from the fact that depletion mode MOSFETs can be (and I have seen them) operated with gate to source voltage swinging not only negative to cutoff the drain to source channel but also positive to turn them more "ON."

This EETimes article authored by a technical writer from Advanced Linear Devices is well written and states the following within it.

Unlike enhancement-mode transistors, which are "normally-off" devices, depletion-mode MOSFETs are "normally-on".

A completely unique feature of depletion-mode MOSFETs is that they can  also be made to work in the "enhancement-mode". This is achieved by  making the gate-to-source voltage (V_GS), slightly positive by  a volt or two for N-channel, or slightly negative by a volt or two for  P-channel devices. This allows increased current levels beyond the  normal I_DSS point.

This page on learnabout-electronics.org gives a less thorough but still good (and with pictures) explanation.  It seems to imply that there are variations of N-channel depletion mode devices based on the physical geometry of the gate relative to the channel.  One that can be turned more "ON" and one that is already fully "ON" at zero volts gate to source.

 

Depletion mode MOSFETS are also available in which the gate extends the  full width of the channel (from source to drain). In this case it is  also possible to operate the transistor in enhancement mode. This is  done by making the gate positive instead of negative. The positive  voltage on the gate attracts more free electrons into the conducing  channel, while at the same time repelling holes down into the P type  substrate. The more positive the gate potential, the deeper, and lower  resistance is the channel. Increasing positive bias therefore increases  current flow. This useful depletion/enhancement version has the  disadvantage that, as the gate area is increased, the gate capacitance  is also larger than true depletion types. This can present difficulties  at higher frequencies.

Either way, it might be a little off topic from your original question (unless of course that was your issue after all), but I thought it would be a good idea to clarify nonetheless in case what I stated in my previous post is in fact in error.