I think I got my VFD working but I also have another issue. Seems the push/pull on/off switch isn't working too well. I have to pull it in and out several times in order for it to turn on. As you might have guessed, that part is no longer available. The switch for the 3520B looks similar but has a different part number. Anyone know if they are interchangeable or where I might find a new Push/pull on/off switch?