Replacing a fried preamp, Five String MM

Aloha…I recently had my bass ruined by a hack ‘repairman’. It functioned great before and now I am working with some that appears far more competent. The bass is from 1990 and as a bass player, with zero knowledge on how to source parts/repair a bass, I really need help to find a preamp-motherboard that will get my bass back in working shape. I’m so bummed. Hopefully someone can help. Thanks in advance!