KnowledgeBase | K2500R | Disk Mode, Drives & SCSI


Basic SCSI Guidelines

Question:

What are the basic guidelines in using my K2 with SCSI devices?

Answer:

  1. Never, ever plug or unplug SCSI cables when your equipment is turned on. SCSI cables carry power. The act of plugging or unplugging cables causes momentary short circuits, which can result in damage to the internal circuitry of your SCSI device. The only damage that usually occurs to SCSI hardware comes from static electricity "zapping" SCSI connector pins when the cables are disconnected. The silver colored shell of the SCSI connector on the end of the cable is connected to ground and is safe to touch, but the brass colored pins inside eventually lead to the SCSI interface chip and are vulnerable. One should discharge static from one's body before touching SCSI connectors by touching the 1/4" jacks on the rear of the Kurzweil or another grounded metal object. Any devices connected to the SCSI bus should be turned off when plugging or unplugging SCSI cables.

  2. Including a minimum of 1 foot for internal cabling of each device in the chain, the total length of the chain should not exceed 18 feet. There are some people who suggest that you shouldn't go over 10 feet, but in our experience, if you use good cables and follow the rules of SCSI, you can create a chain up to 18 feet in length (which is what the SCSI specification says is allowed).

  3. No single cable length in the chain should exceed 8 feet.

  4. The first and last device in the chain must be terminated. Poor termination is a common cause of SCSI problems. Having more than two terminators on the bus will overload the bus drivers. This will not cause permanent damage to the hardware. However, poor termination can corrupt the data on your disk. There are two "exceptions" to this rule. If the chain is less than 18 inches only 1 terminator is needed. If the chain is 10 feet or more, the chain may need to be terminated at the 10 feet point, using a pass through terminator. The reason that we say you "may need" to do this is that we have found that some people don't seem to require a third terminator, while others can't get a longer SCSI chain to work without one. The Kurzweil comes internally terminated, and so you will normally want it to be on one end of the chain. The K2000 and K2661 keyboards must be at the end of the chain since they only have one SCSI port. (If you are hooked up in a chain with a computer, the computer will always be the other end of the chain.) If you need to have the Kurzweil in the middle of the chain, the termination must be removed. This should be done by an authorized service center. In the case of the K2000, it involves removing termination resistors. In the case of the K2500, there are several different possibilities - some have termination resistors that must be removed, others have jumpers that get moved. The newest K2500s and all K2600s have a termination switch on the back, so you can disable termination yourself. If you install an internal drive in the Kurzweil, termination must be removed from the Kurzweil. If the Kurzweil is at the end of the chain, termination resistors should be removed from the K2000 and the termination left on the internal drive. This makes the drive at the end of the chain. If you install an internal drive and the Kurzweil is in the middle of the chain, termination must be removed from both the Kurzweil and the drive. If you add an internal drive and the Kurzweil is not hooked to any other devices, termination should still be removed from the Kurzweil. (See the rule about a chain less than 18 inches, above.) External drives may or may not be internally terminated. If a drive is not terminated and is on the end of the chain, you can purchase an external termination clip, which plugs onto the second SCSI port (most drives will have two ports). Some drives also have an automatic termination feature - if you only have a single SCSI cable plugged in, the drive terminates itself, but if you plug in a second SCSI cable, termination is turned off.

  5. Use only true SCSI cables - high quality, twisted pair, shielded SCSI cable. Do not use RS232 or other non SCSI cables. The majority of SCSI cables we've tested were poorly made and could cause damage to data transferred to and from the disk. Nearly all the SCSI data problems we have encountered have been due to bad cables that didn't twist pairs of wires properly. Good cables that use twisted pairs of wires and twist each SCSI signal wire with a ground wire are essential to reliable data transfers to and from the disk drive.

  6. Impedance mismatching between cables from different manufacturers can cause problems. Avoid this when possible by getting all your cables from the same manufacturer.

  7. Each device in the chain (including internal hard drives) must have its own unique SCSI ID. For the SCSI1 and SCSI2 protocols, there are 8 ID numbers (0-7). For SCSI3, there are 16 ID numbers. The Kurzweil is SCSI1 and SCSI2 compatible. If you have a SCSI3 device, it should be backwards compatible with SCSI1 and SCSI2, but you should make sure to set the ID numbers to 0-8 if you want the Kurzweil to be able to access that device. The default Kurzweil ID is #6. Macintoshes use ID 7 and SCSI cards for PCs are also normally set at 7. The internal drive of a computer is normally set at 0. For an external drive, there will usually be an external switch which allows you to choose the ID, although with some drives, it may have to be done by opening the drive and changing jumper pins. Most drives will allow you to choose any ID, although there are some which limit your choices - for example the Zip drive only gives you the choice of 5 or 6. You can change the SCSI ID of the Kurzweil on the MIDI Receive page, but we recommend leaving it at 6 and changing your other devices if needed, since each time you hard reset the Kurzweil, it returns to 6. If you forget to change it after a reset and have a SCSI ID conflict, you can lock up your SCSI chain and forget the reason why. One thing to watch out for if having a hard drive installed in the Kurzweil - many fixed drives come set with their default at 6 (the same as the Kurzweil). Make sure your service tech knows to set the ID to a different number (this is normally done by moving jumper pins on the drive). One curious side effect of this problem - if the internal drive is set to the same number as the Kurzweil and you have nothing else in the SCSI chain, then you will see the drive show up on every ID except for its own (the Kurzweil shows up on that ID, since it is also on the ID). If you do have more than one device with the same ID, the Kurzweil may lock up when you scroll through the SCSI numbers in Disk mode, or if you are in a chain with a computer, it may not boot up at all. If you have more than one Kurzweil, they can be on the same chain and both be able to access any drive in the chain (though not at the same time). Make sure to change the ID on one of them. If you are having problems getting the Kurzweil to see a device on the chain, sometimes just changing its ID to a different number may fix the problem, even there was no device ID conflict before. There is no logic to this phenomenon - it's just another SCSI weirdness. As a general rule, we recommend only changing the ID of a drive when the system is powered off. It is possible (although unlikely) that data could be corrupted if the ID of a drive is changed while it is turned on.

    Theoretically all eight SCSI IDs can be used, however, we often hear of users having problems with more than 5 IDs. This may be more of a result of not following all the other rules (especially concerning cables), but some SCSI devices seem to be picky. We have also gotten reports from users who state that they can only get their SCSI chain to work when their devices are hooked up in a specific order. Other than having the two ends of the chain terminated, order should not matter, and yet it does for some people. This may be due to impedance variations in the various units, varying internal cable lengths, etc. The bottom line is that if you are having problems getting your chain to work and you have followed all the other rules, try changing the order of the devices.

  8. If the Kurzweil is in a chain with the computer, power up the Kurzweil and other devices before booting up the computer. Some people report that they can't get their computer to boot up if the Kurzweil or other devices are turned off, while others are able to do this Your best bet is to have everything turned on.

  9. Like with any disk that is read to and written from many times, the data on a Kurzweil disk can become fragmented. If the disk becomes severely fragmented, there is a chance that the file allocation table can become corrupted and some or all of the files unreadable. For this reason, we recommend that every so often you back up all your data to another drive and reformat your disk. Or, if the disk was formatted in DOS from a computer you can run an optimizing/deframenting a program to maintain disk health.


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