68 pin SCSI in Amiga

[BLTCON0]

My GVP A2000-HC+8 doesn't detect Hitachi 73GB SCSI 68pin
I used SCSI 68 Male to IDC 50 Male Adapter. I enabled TP/Force SE but they didn't help.

Since it has a "force SE" jumper (force Single-Ended mode) it means it's an LVD (low voltage differential) drive.
These drives never have onboard termination. The "termination power" jumper is just to provide power to a standalone terminator, plugged at the end of the cable.
This also brings another implication into play:

Wide-SCSI bus (= 68 pin = 16 bit) is conceived as an extension to the older narrow-SCSI bus (=50 pin = 8 bit) standard. Actually, commands are still transferred in 8-bit 5 MHz async mode, regardless of advertised bus speed. The wide transfers (16 bit) or faster transfers (10 mhz Fast, 20 Mhz Ultra) are purely for data transfers.

So a 16-bit bus is more or less an 8 + 8 bit bus, with a low-byte (corresponding to operation in 50 pin narrow SCSI mode) and a high-byte (used in 68-pin wide SCSI mode).

Most 68-pin drives do require the presence of so-called bias-voltage on ALL the scsi lines (both low byte and high byte ones) in order to successfully init. This means that when in narrow mode, they require a special 50-68 adapter with high-byte active termination, which (as a side effect) will provide said bias voltage (assuming Termination Power exists, of course, but this can be set).

Alternatively, in lack of such an adapter, one can place the 68-pin drive with a simple (passive) 68-50 adapter LAST in the chain and enable its onboard terminator, which will have an identical side-effect.

Unfortunately, LVD drives by design don't have onboard termination, so this trick can't be used in your case. Using a wide active external terminator will not have the desired effect. Your safest bet is a (more expensive) high-byte terminated 68-50 adapter, plus (of course) active 50-pin terminators at both ends of the controller's 8-bit bus, with the drive (again of course) in SE mode.

Seagate wide drives were a distinguished exception - they universally worked fine in narrow mode, without requiring bias-voltage.

[BLTCON0]

@LoadWB
Yes indeed, back in the day (when I was all about SCSI) they were about 3x the price of regular ones, so indeed they aren't 'expensive' but just 'more expensive'.
I actually corrected it right away but you posted faster than your shadow :-)

Furthermore, as today SCSI is mostly gone, I guess they can occasionally be found dirt-cheap as stock surplus or whatever - the culprit (most often) being with the seller unable to distinguish between passive and terminated ones.

[BLTCON0]

@LoadWB
Very true. Which brings forward a terminology issue/dilemma, too.

My preferred usage would be "adapter" when only the connector's physical format is changed, but the physical (electrical) protocol/signalling remains mostly unchanged (mild alterations such as voltage level conversion wouldn't the "adapter" concept).
Otherwise it would be "converter".

If such a clear distinction was universally adopted and followed, there would be no confusion.

For example, if someone sold a USB-to-PS2 *adapter*, it would be implied that it's just wire-through and the protocol conversion (or selection) is deferred to the device (e.g. a keyboard or mouse in this case).
Same for S-Video to Composite, HDMI-to-VGA etc adapters (where a subset of the S-video / HDMI connector pins must alter -if supported by the graphics hardware- their protocol/signalling significance at the root level, so only a passive wire-through "adapter" is then needed).

If on the other hand it was sold as a USB-to-PS2 *converter* it would be implied it's an active device meant to convert from a specific protocol into another specific protocol.

But as nothing is explicitly set in stone, the terms are more often than not interchangeable and confusion prevails.

[BLTCON0]

Well, the adapter didn't work with Adaptec SCSI card too:
https://www.amazon.com/Monoprice-100077-SCSI-HPDB-Adapter/dp/B001TIQ8G2

That's a passive adapter. No good for your case as I already wrote.

I'll try to find this next time:
https://www.aliexpress.com/item/SCSI-SCA-80-Pin-To-SCSI-68-Pin-IDC-50-Pin-Adapter-SCSI-80-68-50/293779398.html

Why would you do that? You said your drive is an 68-pin one, not an SCA 80-pin one. Even if you had a SCA drive, the story wouldn't end with this adapter.

For your setup, ideally you should desolder the onboard passive terminator of the GVP card and use dedicated 50-pin *active* terminators at both ends of the cable. It should look like this:

{IDC1}Term1-----{IDC2}GVP 50pin-----......--------{IDC3}[high-byte adapter + your LVD drive]----{IDC4}Term2

- Term1, Term2 are something like this.
- The high-byte terminating adapter is something like this.
-So you need a cable with 4 50-pin IDC (female) connectors.
IDC1 is where Term1 gets plugged.
IDC2 connects to GVP's onboard 50-pin header
IDC3 connects to the 50-pin outlet of the 50-68 high-byte adapter (the 68-pin outlet connects to your LVD SCSI drive itself, the drive must have TP enabled and must be set for SE mode)
IDC4 is where Term2 gets plugged
-Cable segment between IDC1 and IDC2 must be short, the same for IDC3 to IDC4 (about 5 cm). IDC2 to IDC3 length doesn't matter much (well, it still shouldn't exceed 1.5m)
Good custom cables here.

Remember to set TP (this will provide the necessary power for the standalone active terminators Term1 and Term2) and to force SE just in case the drive doesn't autoconfigure itself in SE mode.

If you decide to skip desoldering the onboard passive terminator of the GVP card, then you only need your cable to match the IDC2-IDC3-IDC4 configuration, and of course you skip using Term1. I'm not actually advising against this configuration, it should still work OK.

That's about it.