I have a Marquis Voyage Ultimate Series spa that I purchased in 2000. Today, I checked it and the control panel display is blank. Last night, everything worked properly.
I confirmed that I have power to the circuit board and both fuses have continuity. I am assuming the topside control panel is the problem. Is there anyway to check it or do I just need to replace it?

Remove the door on the same side of the touchpad, then trace the cable back to the control box. Most touchpads use a flat "rj45/telephone-style" cable with a clear latching plug on the end. Others use a mini-din.

Mini din connectors can sometimes have a loose connection if the ground wire (connected to the outside ring of the din plug) looses connection. You could try tapping the end of teh din plug VERY slighty to make it not quite a perfect circle (slightly oval). This can improve the connection and stop the TP going blank.

Assuming the pumps are still coming on to heat the pool etc, then I'd suspect teh topside to be at fault, especially if there is evidence of moisture/condensation in there...

The main fuse beneath the circuit board was bad. The spa works properly now. Thanks for the help.