BA356 shelves and TERMPWR

[Adrian Graham_1]

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 a couple of RZ disks 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, everything spun up when the Alpha was powered up.

However, while the TLZ's could be seen at the dead sergeant prompt (>>>)
VMS 6.2 wouldn't configure them so $show device mk produced nothing. On swapping one of the tape drives for
another spare all of a sudden the whole shelf came to life even when the Alpha was off, 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 (with KZPBA) 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 tape 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?

Thanks in advance.

Adrian