DEC BA356 termpwr oddity

Hi folks, I came across weirdness this morning with an 8-bit BA356 shelf and some TLZ09-VA tape drives....hopefully someone here has seen it before. Basically, said BA356 had an RZ disk of indeterminate size (I didn't look :) and 4 TLZ09s; the shelf has a BA35X-MG 8 bit personality module and is plugged into an Alpha 3000-300LX. All well and good. However, while the TLZ's could be seen at the dead sergeant prompt (>>>) VMS 6.2 was having none of it. On swapping one of the tape drives for another spare all of a sudden the whole shelf came to life and VMS was happy. The only difference between this last drive used and all the others was that this drive had the TERMPWR jumper installed (default config I thought) and so was providing TERMPWR to the backplane. Since the SCSI adapter in the 3000-300LX should have been providing this power and the personality module in the shelf provided termination why should this jumper make so much difference to the bus? It's not a length issue since I've duplicated the setup this afternoon using a DS10 and half metre cables. Also I thought too much TERMPWR was a Bad Thing. Interestingly, swapping the shelf for a blue UltraSCSI BA356 and using an Ultra personality module made the problem vanish and the drives were happy whether there was a TERMPWR jumper installed or not. Since these drives are destined for non-ultra environments do I have to crack them all open and fit the jumpers or is there something I'm missing? Ta! -- adrian/witchy Binary Dinosaurs creator/curator www.binarydinosaurs.co.uk - the UKs biggest home computer collection?