Yeah, I understood your problem, this is why I asked about the other displays. There is a low battery protection mode that shuts down all the VFDs on the car (the IPC is the one commanding them off trough the data bus, shuts down his own and command the others). This happens when the IPC sense the voltage dropping below 9.? Volts.
In your case seems to be a problem with the IPC.
Read
this basic information about VFDs so you have an idea in what you are getting into.
Unfortunately I haven’t study the IPC circuitry enough (especially the ‘98+ models) but you might get by replacing boards from a used working IPC and keep the odometer (that in case you really want to keep your IPC). Probably you will get by easily with completely replacing the IPC and had the odometer reprogrammed.