VAX 750 tbuf machine checks

[RSanders at USGS2-MULTICS.ARPA]

I've been mostly ignoring the stuff about mchk 2's on VAX 750s because
mine rarely showed more than 2 per week.  However, last week we added a
TC7000 Massbus tape controller, so I genned a new kernal to talk to it.
Magically, this new kernal (not currently being used), generates mchk
2's roughly every 2 minutes - quite unacceptable.

Now, the question is, can I avoid the Rev 7/load microcode upgrade and
still talk to my new tape drive?  Obviously, something about the new
kernal is really pounding on the tbuf parity problem.  Any suggestions?
What was the final resolution to the discussions, anyway?

-- Rex

p.s.  config files available on request.

p.p.s.  obviously, we are running 4.2 BSD.