I have a 1986 SE with a dead internal HD (original 40MB Quantum).
My plan is to pull a rarely-used Maxtor 120MB HD which is currently in an external SCSI case using an external terminator. Works perfectly.
Does this Maxtor drive need to be internally terminated to work as an internal drive in the SE? How can I tell if the Maxtor drive is internally terminated?
Also, the SE is missing the PRAM battery. Will it work without a PRAM battery installed?
Yes, the drive needs to be internally terminated. Both physical ends of the SCSI chain need to be terminated. The hard drive, at the end of the internal SCSI cable is at one end of the chain. The other end of the chain is the last device on the external SCSI chain of cables.
We usually cheat a bit when there are no external devices installed and leave the external end (which is now located at the external SCSI connector) unterminated. This works because the internal SCSI cable is very short and one end of the chain can be left unterminated if the overall cabling is very short. Technically, we should install a DB25 terminator on the external SCSI port when there are no external devices connected.
Termination on the hard drive itself is set using one of two methods. Either there is a jumper which you install which turns on termination on the drive, or there will be two or three resistor packs which must be installed to enable termination. If the latter, you are probably out of luck because it is unlikely that a drive in an external enclosure has the resistor packs included somewhere.
If you don't know what jumpers are, post a follow up question.
Resistor packs are multiple resistors built into one package. I've seen them in black, green, red, yellow/orange and blue. They look like a axially squished tube about 1" long with several wires/pins coming out of one edge. On hard drives which use them, there will be a row of holes into which the pins should be inserted to install the resistor packs.
The location of the jumper and the type, size and location of the resistor packs vary from drive to drive, although the resistor packs are usually located near the SCSI connector and parallel to it, in my experience.
So, you usually need to find a user's manual or datasheet for the specific hard drive you have to identify the termination method.
If you are fortunate there will be a pair of pins on the drive for a jumper which is clearly labeled TE, which stands for Termination Enable. TP is different and is for Termination Power.
Another alternative to enabling termination on the drive is to use a terminator on the internal SCSI ribbon cable. This can take one of two forms. There are pass-through internal terminators and there are terminator blocks.
A pass-through terminator has a connector at each end. One end plugs into the end of the internal SCSI ribbon cable. The other end/connector of the pass-through terminator plugs into the hard drive. Hence the terminator provides termination right at the hard drive connector.
A terminator block simply plugs into the end of the SCSI ribbon cable. To use an internal terminator block, you need a SCSI ribbon cable with one extra connector. You plug in the cable, attach your hard drive(s) and leave the connector at the end of the ribbon cable empty. Then plug the terminator block into the connector at the end of the ribbon cable. Voila. Termination is now present at the end of the SCSI cable.
Internal terminators which go on ribbon cables are not as easily found as external terminators, but they are available.
