Problem with Nat Semi ICM-3216

I recently picked up a couple of ICM-3216s and am hoping the following might make sense to someone more familiar with them. There are two systems comprised of a CPU board, one 4MB memory board, and an ICM-SIO-M-08 board with its own 32016, 32201, and four 2681 DUARTs for 8 serial ports. The SIO board in front of me is a 980600014-001 Rev D (the 001 and D are hand written) The EPROMs in U5 and U6 show Rev B on their labels, and I can give the full P/N if it will help. When retired from service several-many years ago, these machines were timesharing hosts and used all these serial ports. Now when I try to power up either system with the SIO board in the stack, the system won't initialize. If I remove the SIO from the stack the system will initialize and I can boot Unix on one box, or talk to the monitor on the other (disk won't spin). Does this make sense to anyone familiar with these systems? I suspect someone else has seen this, given the way it's impacting both systems... I suppose I'll start checking out the third box, which lacks an SIO, and see what it does with it. Thanks for any thoughts, or even unrelated reminisences about the ICMs or the 32k in general. --Steve. Steve Jones spamfree.crash.com!smj Arlington, Mass. CRASH!! Computing (any spambots parse bang paths?) +1 781 xxx yyyy "Chaos will ensue if the variable i is altered..." - SysV Programmers Guide