Removing SCSI Drive from 7600 - termination questions

[ziggy29]

I've added a much faster ATA/IDE drive to my 7600 and would like to remove the SCSI drive from the unit.  I remember from the old days of this stuff that SCSI chains have termination issues at times.  My understanding is that the internal chain goes from the SCSI card to the internal CD-ROM to the SCSI HDD.  The HDD should be terminated.  If I remove it, I believe the CD-ROM needs to have termination, whereas it shouldn't have it now? 

So, question is -- what, if anything, do I need to do or set on the CD-ROM in order to properly terminate it once I pull the SCSI HDD out? 

[DieHard]

Here is some info I posted in the past...

A few quick notes on SCSI termination and term power...

Always OVERLOOKED, check Term POWER first
Make sure your SCSI controller or at least one your devices provides "Term Power' to the SCSI Bus.
Term Power is NOT the same as termination, term power is a voltage  (+5 VDC, or LVD requires a 3.3 VDC) that travels down the SCSI bus used to power the SCSI terminator. So check the settings of your SCSI controller and enable Term Power. You need at least 1 device supplying term power... and I personally recommend only 1 device supplying Term Power unless your  SCSI chain (all cables together) are longer that 9 feet. (Having more than one device on the bus providing term power often desirable to reduce problems of voltage "droop" caused by IR losses in long SCSI cables). But remember, some devices have a  Termpwr fuse (PTC Resistor) which goes to high resistance if too much current flows while providing Termination Power to the SCSI devices. FOR MOST SETUPS, Turn on the Term Power of your SCSI controller and turn it off on all other devices.  If your controller does NOT supply temp power, turn it on via a Hard drive or other device(s).
Quote

    For the SCSI Bus to work properly with controllers that do not supply termination power, the device itself, would have to provide Term power to the SCSI Bus. You will need to check your SCSI device documentation on how to set term power for the specific device. Most SCSI devices provide termination power, but not all. To ensure, please check with your product documentation or check with the device manufacturer.

Most of Adaptec SCSI controllers do supply termination power (Term power) to the SCSI Bus, but you must research it !

Now that we have that done... let's review Termination rules again

TERMINATION RULES:
1) As stated in another post, the last PHYSICAL device in the EXTERNAL SCSI chain Must be terminated, makes sense, think of the SCSI chain, like an old coax Ethernet, you don't want SCSI signals to attempt to shoot past the last device, hence termination is needed.... duhhhh

2) As stated in another post, the last PHYSICAL device in the INTERNAL SCSI chain Must be terminated, makes sense, think of the SCSI chain, like an old coax Ethernet, you don't want SCSI signals to attempt to shoot past the last device, hence termination is needed.... duhhhh

3) Obvious, but sometimes overlooked, If there are External and Internal devices present, make sure the SCSI card is not Terminated (sometimes requires jumper removal or a dip switch set, or a SCSI BIOS setting).

4) Also Obvious... If your internal SCSI Cable has a big square block on the end of it that is a SCSI terminator and NO device should be terminated.

5) Problems... if any device midway in the external or internal chain IS terminated, then you will have all sorts of issues and shit will not function correctly... if at all; Check Hard drive jumpers and or remove long red terminator blocks (if present)

6) IDs in any order are OK as long as ther are unique (per channel), but try to number the card as SCSI ID 0 and increment starting from the card outward, so the first connected device is ID 1, next ID 2...and so on... since the internal channel and external channels are separate, you can use the same method for each channel without a problem or you can use a different starting point for external stuff to avoid confusion.... for example, a system with 2 internal HDs and 1 external Jazz drive...
Card is ID 0, first internal HD is ID 1, 2nd HD is ID 2 (Terminated or end of cable terminated)
Jazz is ID 6 and terminated.
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« Last Edit: August 28, 2014, 12:32:42 PM by DieHard »

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http://macos9lives.com/smforum/index.php/topic,1712.0.html