Term power mod for TT installed

[Steve]

Hi,

Just sharing a photo of the term power mod for the TT that I installed tonight. This adds term power to pin 26 of the internal header and pin 25 of the external port. By having this I am told that I can actually remove the internal resistors entirely and use an external SCSI terminator instead (Frank tells me)

Hopefully all this will make my TT SCSI more reliable, I will report my findings later.

Diode is a 1N4001 and fuse is an N25j.

PXL_20211210_204003169.jpg (521.71 KiB) Viewed 4233 times

Original diagram (only showing internal wire pin 26 in this picture, I also wired up external pin 25 as per Frank's suggestion)

TT SCSI PORT ACTIVE TERM PWR MOD.jpg (41.21 KiB) Viewed 4230 times

[Steve]

Update on SCSI stability:

This has fixed everything, my drives are all detected, I can partition no issues, Kobold copies no issue, integrity checks are all good, RaSCSI is working perfect!

[mrbombermillzy]

Great to hear you have it all sorted now @Steve .

[exxos]

Might be worth copying to tweaks and fixes section ?

[Steve]

Okay will do soon.

[mikro]

So when you had the resistors in there and (terminated) RaSCSI on the internal SCSI bus it didn't work but as soon as you did this mod + removed the resitors + connected an external (active) terminator it started working?

EDIT: Now I see in the RaSCSI's schematics that it has its own TERM POWER circuitry, basically identical to yours, so perhaps it would work also without this patch, just sourcing from RaSCSI's TERM POWER instead of TT's? (I guess RaSCSI has a jumper for it)

[frank.lukas]

The patch is not necessary when the internal SCSI Drive and the external drive provide termpower to the bus. But standard is that the SCSI Hostadapter (ISA or PCI) provide always termpower to the bus. It is also allowed that several drives deliver termpower. Therefore the diode ...

[Steve]

..

[exxos]

I'm a bit lost now. So you did the mod, and there is no termination now internal or external ? In which case the mod wouldn't be doing anything anyway now ?

[Steve]

So when you had the resistors in there and (terminated) RaSCSI on the internal SCSI bus it didn't work but as soon as you did this mod + removed the resitors + connected an external (active) terminator it started working?

EDIT: Now I see in the RaSCSI's schematics that it has its own TERM POWER circuitry, basically identical to yours, so perhaps it would work also without this patch, just sourcing from RaSCSI's TERM POWER instead of TT's? (I guess RaSCSI has a jumper for it)

I've always had the RaSCSI's term power enabled.

@exxos FYI, with or without the internal resistors, the mod provides term power down pin 26 and 25.