My book for the 3T for this fault says = The alarm occurs if a parity error is detected when reading data from RAM which stores parameters and programs on the master PCB.
The first thing said to try is depress the delete key while turning power on, this clears all part program areas, if the alarm dissapears, reload programs.
If the alarm does not go away with the previous procedure, turn the parameter write switch and push the DELETE key and RESET key while turning on the power.
This clears offsets, programs, and parameters, which requires that all parameters etc have to be re-loaded, if this does not cure it says that.
1/It could be a memory problem.
3/Power Supply Unit.
CHeck the power supply voltages especially the 5vdc.