David Cook
Well-known member
I bought an external HD on eBay a while back. During restoration of a Mac Plus, I struggled to get a solid-state drive (MacSD) to be recognized, despite using external power. So, I pulled out this old APS hard drive with "DaTerm Digital Active Termination".
Despite flipping the dip switch on the back of the drive, SCSI Probe complained that the SCSI bus was unterminated. Furthermore, the little green LED on the back of the drive never lit up. Attaching an external terminator with status lights -- also resulted in no LEDs turning on. Something is wrong.
To open the case, pull off the four bottom feet and remove the screws. Pull off the top two rear feet and press down on the plastic latches to release the cover. The metal shield is then removed by bending the four tabs on the sides.
Upon removing the cover, I found a cable detached (see purple arrow below). Unfortunately, the cable is not keyed. A multimeter showed an entire row on the SCSI port was connected, which are the GND pins. Powering on the drive showed +5 and GND on the cable. (As expected, the black wire was GND.). A little more multimeter testing showed the bottom pin is connected the GND SCSI pins, so the black wire should be plugged into the bottom pin. Plugging the cable in restored SCSI power on the terminator pin (and thus the external terminator with status lights lit up). However, the green LED on the back of the drive remained off.
Peeling off the DaTerm label reveals two screws. Removing those screws and loosening the internal hard disk allows the rear connector PCB to be removed.
See image below...
And now we see that the green LED wasn't lighting up because it got smashed somehow. It was simple to desolder and replace. After that, flipping the DaTerm dip switch turns on and off the LED (and SCSI termination) as expected.
A couple of closing thoughts.
1. The APS enclosure provides +5V SCSI termination power through a fuse and to the proper SCSI pin, regardless of whether SCSI termination is enabled. So, if you have Mac that doesn't provide termination power (such as a Mac Plus or PowerBook), this enclosure will do the job even for additional SCSI accessories down the chain. If you don't want this feature, unplug the internal cable.
2. The APS enclosure provides active termination on or off through the dip switch.
3. The internal drive is just an ordinary SCSI hard disk. You can swap it out as desired.
4. Although the Mac Plus now recognized the drive and SCSI probe found the bus to be properly terminated, it still couldn't boot from it. Maybe because my Mac Plus has the slightly buggy v2 ROMs? Maybe due to the expectations of the IBM SCSI drive inside the case.
- David
Despite flipping the dip switch on the back of the drive, SCSI Probe complained that the SCSI bus was unterminated. Furthermore, the little green LED on the back of the drive never lit up. Attaching an external terminator with status lights -- also resulted in no LEDs turning on. Something is wrong.
To open the case, pull off the four bottom feet and remove the screws. Pull off the top two rear feet and press down on the plastic latches to release the cover. The metal shield is then removed by bending the four tabs on the sides.
Upon removing the cover, I found a cable detached (see purple arrow below). Unfortunately, the cable is not keyed. A multimeter showed an entire row on the SCSI port was connected, which are the GND pins. Powering on the drive showed +5 and GND on the cable. (As expected, the black wire was GND.). A little more multimeter testing showed the bottom pin is connected the GND SCSI pins, so the black wire should be plugged into the bottom pin. Plugging the cable in restored SCSI power on the terminator pin (and thus the external terminator with status lights lit up). However, the green LED on the back of the drive remained off.
Peeling off the DaTerm label reveals two screws. Removing those screws and loosening the internal hard disk allows the rear connector PCB to be removed.
See image below...
- A self-resetting fuse for the terminator power on the SCSI pin. Nice.
- Capacitors
- The dipswitch labeled '1' is the only switch connected. It logically enables or disables the Dallas chips.
- The Dallas DS21S07A chips provide SCSI termination through voltage regulation -- thus an 'active' terminator.
- The green LED that wouldn't light up.
And now we see that the green LED wasn't lighting up because it got smashed somehow. It was simple to desolder and replace. After that, flipping the DaTerm dip switch turns on and off the LED (and SCSI termination) as expected.
A couple of closing thoughts.
1. The APS enclosure provides +5V SCSI termination power through a fuse and to the proper SCSI pin, regardless of whether SCSI termination is enabled. So, if you have Mac that doesn't provide termination power (such as a Mac Plus or PowerBook), this enclosure will do the job even for additional SCSI accessories down the chain. If you don't want this feature, unplug the internal cable.
2. The APS enclosure provides active termination on or off through the dip switch.
3. The internal drive is just an ordinary SCSI hard disk. You can swap it out as desired.
4. Although the Mac Plus now recognized the drive and SCSI probe found the bus to be properly terminated, it still couldn't boot from it. Maybe because my Mac Plus has the slightly buggy v2 ROMs? Maybe due to the expectations of the IBM SCSI drive inside the case.
- David
