Display outage

This vehicle has been a backup used for about one to two thousand miles a year to make trips to get hardware and other large items, sometimes pulling a 5'X8' trailer. For about two years, the speedometer has not been working correctly, and then the gas gauge stopped working. However, the digital display has shown reliable data proving that the inputs are still working and it is a problem at the actual gauges or the lines to them. Just recently after starting it, all gauges read 0/minimum as appropriate and the digital display was filled up or all lit. The engine ran fine and drove the same as previous experiences. Is this because the computer broke or is there a separate display chip that failed? What is the best way to check and fix?