There are two versions of the SCSI2SD - the older one has to be jumpered to self power the onboard resistors if the SCSI bus provides no term power (the TT doesn't). The newer one doesn't need to be jumpered to provide term power to itself. Which version of SCSI2SD do you have, the v5.0 or the earlier revision?
Word has it that the SCSI behaviour on the TT is very dependent on the Rev of the motherboard. There was a lot of rework on the SCSI circuits between the early and later revisions. Mine is a Rev H board and it seems not to care too much whether or not the terminating resistors on the motherboard are fitted. Well, sort of.
When I got it there were none fitted internally but I had no problems with the internal SCSI drive (terminated), just like lp's machine. However, I thought it would be a good idea to terminate the TT / external bus as per the 'rules'. I didn't have any resistor packs so I fitted an external passive terminator. Big problems (of course the TT supplies no term power over the D25 so fitting the terminator to the external branch of the T should have made no difference, but it did -internal drive not happy). Then I tried to use an external SCSI device (also terminated), again I had big problems until I enabled self term power on the external drive. Eventually I got some resistor packs and went ahead and fitted them anyway just for sh*ts and giggles. Now, my external (terminated) device and internal (terminated) drive were still happy. This makes no sense.
With the motherboard terminators fitted and external and internal drives both terminated all drives were happy. Without the motherboard terminators fitted, internal and external drives were very picky when both busses were connected, either a drive or a passive terminator. With no motherboard resistors fitted and only external (terminated) or internal (terminated) drive connected either drive was happy. This behaviour is the complete reverse of what I would have expected. My SCSI busses appear quiet no matter what without the resistor packs fitted but with the terminators fitted they seem ring like church bells after a wedding - Go figure.
TT030 10mb/16mb/1Gb, Coco. Falcon 030 Stock 14mb (Lynxman), 1Gb CF. Falcon 030 Stock 14mb (Atari) 170mb IDE. Mega 1 big button (mash up badged Mega 4) 4mb (home cooked RAM upgrade) ICD ADSpeed ST OverScan. Mega 2 big button (4mb), Mega 1 small button (4mb home cooked 72pin SIMM slot), 520 STe (SIPPs), 520 STFM (4mb using a Falcon 4mb board + Blitter).