PDP-11/73 boot issues

Hi all, My PDP-11/73 has started misbehaving after several years of being very stable. It is showing symptoms similar to when I've forgotten to enable the LTC in the past, except this time, it is enable. Power supply seems good - +5V, +12V, all seems there and appears to be stable. I've probed the LTC going onto the backplane and I'm getting 50Hz. It looks a tad noisy, not sure if this is a problem. I will see if I can get a picture of it, but it has very distinct rises and falls, so hopefully that's ok. Looks to be about 50% duty cycle. I've attempted several builds of the kernel, including the out-of-the-box build from 2.11BSD distribution. I've also compiled a shrunk down kernel without a bunch of devices I don't have, but it still fails to work. I am using a SCSI2SD so it's easy for me to copy images and test them in SIMH - they all boot fine in SIMH with a similar setup (mscp, tmscp, 11/73, 1MB-ish RAM). Does anyone have any ideas what might be causing this? I've run out of ideas unfortunately. I'll stick a dump of the boot below, with debug flag passed showing output from autoconfig. I've also tried it without the tmscp card - just CPU, RAM and Emulex UC07 in MSCP mode for scsi disk. I have tried it with less memory, and I've tried removing the halt jumper from the 11/73 board (W5 if I remember correctly) Cheers, Aaron --------- ^C BOOT> DU 0 73Boot from ra(0,0,0) at 0172150 : ra(0,0,0)unix -D Boot: bootdev=02400 bootcsr=0172150 2.11 BSD UNIX #116: Wed Dec 31 18:01:57 CST 1969 root at localhost.2bsd.com:/usr/src/sys/GENERIC ra0: Ver 5 mod 13 ra0: RA81 size=1216601 phys mem = 1179648 avail mem = 959040 user mem = 307200 _hkprobe = 0 _hkattach = 143330 _hkVec = 0 hkintr = 120 _htprobe = 0 _htattach = 143550 _htVec = 0 htintr = 150 _raprobe = 0 _raattach = 34270 _raVec = 34200 raintr = 100 _rkprobe = 0 _rkattach = 144650 _rkVec = 0 rkintr = 130 _rlprobe = 0 _rlattach = 144770 _rlVec = 0 rlintr = 110 _tmprobe = 0 _tmattach = 143610 _tmVec = 0 tmintr = 160 _tmsprobe = 0 _tmsattach = 143740 _tmsVec = 143730 tmsintr = 200 _tsprobe = 0 _tsattach = 143660 _tsVec = 0 tsintr = 170 _xpprobe = 0 _xpattach = 0 _xpVec = 0 xpintr = 0 endvec = 1000 _conf_int = 16124 CGOOD = 14 CBAD = 24 _nextiv = 5500 trap = 4150 _version = 17400 KERN_NONSEP = 0 Grab 177440 = 36556hk ? csr 177440 vector 210 skipped: No CSR. Grab 172440 = 36556ht ? csr 172440 vector 224 skipped: No CSR. Grab 172150 = 0Grab 156 = 240Grab 154 = 100Stuff 14 @ 154 Stuff 340 @ 156 probe ra: return conf_int:Stuff 100 @ 154 Stuff 240 @ 156 ra ? csr 172150 vector 154 bad probe value 224. Grab 177400 = 36556rk ? csr 177400 vector 220 skipped: No CSR. Grab 174400 = 36556rl ? csr 174400 vector 160 skipped: No CSR. Grab 172520 = 36556tm ? csr 172520 vector 224 skipped: No CSR. Grab 174500 = 0Grab 262 = 0Grab 260 = 0tms ? csr 174500 vector 260 interrupt vector already in use. Grab 172520 = 36556ts ? csr 172520 vector 224 skipped: No CSR. xp ? csr 176700 vector 254 skipped: No autoconfig routines. At this point it is stuck no matter how long I wait.