Oh boy, that reg. is old, older than my Ample. Crusiing Equipment disappeared into Heart which disappeared into Xantrex years ago.
You have several boat electrical companies in the Seattle/Everett/Tacoma area. Have you contacted any of them? If lucky they may guide you to an electroncs repair shop. I expect they tell you it will cost more to repair than simply replace.
Take the cover off and see if the board components are potted. Many were potted which makes boards like that difficult/expensive to repair.
If not potted it may be possible to ask around for an industrial electronics repair co.
Those shops often have some extremely good technicians who can figure out repairs without drawings. Nothing to do with boat stuff but I dealt with some stuff like this where the mfgr. were long gone and we needed the mach. to run. I asked around the machine suppliers [machine tools] about who did their electronic repairs.
But be carefull as it may cost more than a good replacement.
I just realized you may be near Anacortes. Have no idea if a suitable co. is in the area but it may be worthwhile asking around there.
E-bay for a used one hopefully.
Unfortunately that's all I can suggest as I do not live in the area.