The FCV-600L doesn't have charting capabilities thus doesn't use a chart card. Even if it was a chart plotter the lack of a chart card won't prevent a unit from powering up. The true test in checking voltage is to measure it on the back of the power connector as you are trying to power up the sounder, but the FCV-600L uses a molded plug so that is not an option for you. So making sure there is no corrosion on the power plug pins and connector will be the best you can do. If this looks OK and it still won't power up, I would take into a Furuno dealer to have them bench test it.