Still looking for a couple of answers to questions for the Heath H-27 floppy controller

OK... so I got this H-27 that locks up the Qbus when it is in the grant chain and works ok (except for interrupts) when it is past the end of the granted devices (one or more blank Qbus slots in-between). I've pulled and tested each and every TTL chip, but can't use the auto chip tester on the Nat'l Semi parts. My questions are this: What are the three jumpers for? (E-1 through E-3, between U11 and U12, and U7 and U8) What bus drivers/receivers directly interact with the interrupt grant chain? If I'm lucky, it's U11 and U7 - I have plenty of 8136 chips. What can I substitute for DS8837 and DS8839 chips, if one of them is at fault? __________________________________________________ Do You Yahoo!? Yahoo! Auctions - buy the things you want at great prices http://auctions.yahoo.com/