HP 7970E tape drive woes

Greetings and a question for the list.... My HP7970E tape drive is *sick* (plus I just blew the 30v supply in my HP2100A, but that's a whole other story about me and Murphy's Laws on getting HP2000 Access up and running). Do others find that resurrecting these old systems causes a propensity to drink excessively? *GRIN* On to the question... The 7970E passes all the mechanical tests via the switches internal to the unit (tape speeds & motion basically). It fails the read/write test portion of the diagnostics (but does pass interrupt/DMA tests so I suspect the interface boards are ok). Is anyone particularly familiar with these beasts and can suggest a course of action? I have all the "theory of operation" and "maintenance" manuals (as well as schematics), but they are two 4 inch thick manuals and a lot of it is way over my head. Hopefully someone can point me in the right direction to at least get me started - or better yet, anyone have a 7970E up and running that would be willing to loan me some boards to test mine via boardswapping?? Thanks for any info (or condolences & empathy) anyone can provide! Jay West