SCA Drive on a "Narrow" Cable

Electrical Interface: --

SCA drives often use "balanced" or "push-pull" drivers and receivers, sensing the difference between the + and - wires as the actual signal. You can get it to work on a 68-pin ["Wide"] bus by setting the Drive or the Bus or both to "Single Ended". Many adapters set the appropriate signal for you by grounding a pin on the connector. Your Drive has a jumper to set it to Single-Ended, labelled "Force Single Ended".

Wide-68 to narrow-50 --

Sometimes this is very difficult, but in this case, your adapter should be doing the pin-swapping part of the conversion for you, and your drive has a jumper labelled "Disable Wide Negotiations". This tells the drive just to give up and go narrow. IBM specifies in other documents that you should "float" the high 8 data bits Bus signals. Your adapter may terminate them, but it looks like the drive is prepared to ignore them.

Termination, which is not the same as Term Power --

Single-Ended termination is about the same as Active termination. It can be done with a "Regular" SCSI terminator, or with another drive on the bus. But this drive is NOT prepared to do termination itself, no matter how you set the straps. The terminators for LVD drives are non-trivial in size, so the manufacturers of LVD drives almost always omit the terminators, and leave it as an exercise for the end-user.

You can set the drive to supply Term Power, but this just squirts extra 5 Volts from the drive onto the cable pins reserved for it. Wherever the terminator is actually located, it picks up the 5 Volts from the cable pins reserved for it, and uses it to power the terminators.

You need a terminator at the {Last device/end of the cable}, or another drive at the end of the cable with a termination [not just Term Power] strap setting.

Misc strap settings --

That drive has a Disable Unit Attention strap, which should be set. Unit Attention has not been a serious problem since the Mac Plus, but things work better without it.

Spin up and Spin Delay --

Many of these drives use a lot of power when they spin up. So some of them have a feature to wait ( n seconds * SCSI_ID) before they spin up. If a cabinet full tried to spin up all at once after a power failure, they would draw so much power the fuses in the cabinet would blow.

IBM likes to let the software command the drive to spin up, but the Mac likes it to be already spinning. So I think you set the strap to Spin up.

Cables --

SCA drives should be used with a backplane or a small card that accepts the data cable and a regular 4-pin Molex Hard Drive Power connector and some straps for the SCSI ID and drive spin up. They should not be used with 80-pin cables, because the wires in those cables are not big enough to supply all the power the drives need.

This drive can transfer 40 MB/sec. At that speed, the cables must be short. Total Cable allowed for all devices at those speeds is about four feet. When Apple uses these drives, they use a cable made of special plastic to control the capacitance between adjacent wires. Your internal SCSI can only transfer data at about 5 MB/sec, so "regular" gray ribbon cable should be OK. But there is only one internal/external bus in a beige G3, so you need to count all the cable, and keep it as short as possible.

I hope this helps and is not just word-salad

What are you using for a terminator?

Have you tried the excellent free utility, Mt. Everything?

http://www.overnet.de/hhp/mte/

Is it possible that the on-the-adapter terminator just takes care of the [unused] High byte, and lets the rest float, i.e., does not provide proper termination for the main [low] byte?

To provide termination, the adapter must have the SIP Resistor packs in place, in all locations referenced as CN4.

One telling diagnostic of any drive is whether it will tell you BOTH its Make & Model, and its SIZE. If it will not, it is likely the drive is dead.

Mt. Everything has some diagnostics in it. I have had it tell me that a drive was not terminated. If it is NOT telling you that, then termination may not be the issue. Can it determine the drive's SIZE?

It does not have to mount to tell a disk utility/formatter its capacity.

Most manufacturers use the same controller for several different models. They put the list of bad blocks and the size parameters in a convenient place, which is, ... well, ... on the platters, in a section reserved for such stuff but outside the data area they tell you about.

When a drive cannot tell you its Make & Model AND its Size, it has suffered a failure that prevents it from accessing the parameters (like size) and the bad blocks information.

Unfortunately, this means it has died.