Ultra 60 NVRAM

Hi all,

Not strictly a NetBSD question, but I imagine someone here must know the 
answer to this...

Trying to revive my Ultra 60 for NetBSD purposes, I found that the NVRAM 
battery had died.

I ordered a M48T59Y-70PC1 chip to replace it with, but after I changed 
it the machine refuses to boot (even the power LED doesn't come on).

The new chip is a -70PC1D rather than a -70PC1U. I don't think I've 
fried anything - the machine still boots fine with the old NVRAM chip.

So, is the D rather than U significant? Is the chip just defective? 
Should I do something to reset the NVRAM? (I tried Stop-N at boot, but 
that doesn't seem to have any effect)

any light shed on this appreciated,

   Jaap