SCSI Success
SCSI Success
I've now connected the disc to the Beeb via the Akhter host adapter. As you can see, this disc has had a previous life as an MDFS disc. It's blank, this was one of my BeebShop stock of ready-formatted MDFS hard drives, but it's now about to be re-assigned as a BBC Micro hard drive.
A couple of important points here. Although you can't see it in the picture, pin 34 of the SCSI 50-way ribbon cable is something of a problem. In all SCSI implementations, pin 34 is connected to ground. In 1981, or thereabouts, Acorn decided it would be fun to shove 5V down this pin for powering test equipment. The end result is that if you connect a BBC micro host adapter to a SCSI disc via a 50-pin ribbon cable without doing anything, the cable will overheat and begin to melt.
This has happened to me many, many times over the years - even leading to the Great FileStore Fire of 2003, when it really oughtn't to have happened - so I now adopt the practice of cutting through pin 34 of the SCSI ribbon cable so it isn't connected.
One more thing - the Acorn SCSI implementation is extremely fussy about termination. If the termination isn't to its liking, ADFS will ignore your disc just as if it was a SCSI-2 disc without the change defnition command applied. Both ends of the SCSI bus must be terminated. As you can see, terminating resistors are fitted to the Akhter host adapter board. The disc end also needs to be terminated. For some reason, it appears that "double" termination is required - here I've got an active SCSI terminator plugged into the back of the Seagate drive, but in addition, the drive's own termination is enabled.