One thing I certainly don't want to do is pour cold water on someone's enthusiasm. However, if you're unfamiliar with measuring voltage I would suggest it would unproductive (and maybe dangerous to both you and the machine) to delve any deeper into the diagnosis. Not at least until you've got some more basic electronic knowledge anyway.
This book might help. "Electronics for dummies". It's aimed at the hobbiest who is just starting on this stuff. I THINK you can download it for free here:http://www.ebook3000.com/Electronics-Fo ... 22624.html
Either way, given its rarity (hence scarcity of spare parts), non-standard CPU and lack of a wide body of people familiar with the machine, a HP85b is likely to be challenging to fix even for the experienced technician.