Just tried with your kernel, still fails at exactly the same point. Damn :-(

>>boot

NetBSD/pmax 1.5.2 FFS Primary Bootstrap

NetBSD/pmax 1.5.2 Secondary Bootstrap, Revision 1.3
(root@medusa.thistledown.com.au, Aug 19 15:12:41 EST 2001)

Boot: 3/rz1/netbsd
1942808+61104+367740 [89+76464+62853]=0x26631c
Starting at 0x80030000

[ preserving 139984 bytes of netbsd ELF symbol table ]
Copyright (c) 1996, 1997, 1998, 1999, 2000, 2001
    The NetBSD Foundation, Inc.  All rights reserved.
Copyright (c) 1982, 1986, 1989, 1991, 1993
    The Regents of the University of California.  All rights reserved.

NetBSD 1.5.1 (DS5k240) #0: Fri Oct 26 13:09:45 PDT 2001
    root@zerberus:/usr/src/sys/arch/pmax/compile/DS5k240
DECstation 5000/240 (3MAXPLUS)
total memory = 24576 KB
avail memory = 19876 KB
using 332 buffers containing 1328 KB of memory
mainbus0 (root)
cpu0 at mainbus0: MIPS R3000 CPU (0x230) Rev. 3.0 with MIPS R3010 FPC Rev. 4.0
cpu0: 64KB Instruction, 64KB Data, direct mapped cache
tc0 at mainbus0: 25 MHz clock
ioasic0 at tc0 slot 3 offset 0x0
le0 at ioasic0 offset 0xc0000: address 08:00:2b:2a:2d:65
le0: 32 receive buffers, 8 transmit buffers
scc0 at ioasic0 offset 0x100000
scc1 at ioasic0 offset 0x180000: console
mcclock0 at ioasic0 offset 0x200000: mc146818 or compatible
xasc0 at ioasic0 offset 0x300000: NCR53C94, 25MHz, SCSI ID 7
scsibus0 at xasc0: 8 targets, 8 luns per target
px0 at tc0 slot 0 offset 0x0: 2D, 5x1 stamp, 8 plane
^C
>>