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AuthorTopic: A3000 external scsi termination  (Read 1410 times)

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Offline T3000

A3000 external scsi termination
« on: July 18, 2007, 08:33:13 PM »
Hmmm...   Not to hijack theHelp needed from A3000 users ! thread, but...

Quote
Boot_WB wrote:
The a3000 has two "caterpillar"-like terminator resistor packs on the motherboard.
If these are missing, then you will need to have an additional  terminator attached to the external 25-pin scsi port.
Quote


Does an external 100mg ZIP drive have active or passive termination? Would I need to terminate the Zip on the end of the external scsi chain? Also the inline terminator that goes on a scanner at the end of a scsi external chain, is that active or passive?

My A3000D has been experiencing random scsi locks and checksum errors with the CDrom, ZIP and scanner on an external scsi chain. The internal 4gig HD has the shortest available cable and the drive is terminated. I'm not sure the mobo has the resitor packs, will have to look now that the cover is off due to many scsi locks on boot up after unpacking and cabling the system after recent household move. My A3000D never liked being moved around, even from one desk top to another...

Whats the deal on scsi chain lengths? 7ft? with each device counted as one foot worth?

To get the HD to boot, couldn't get to the early startup, I unpluged the external scsi cable and installed the 25 pin terminator pack. Fired up. Next added the Zip drive and terminated it. Fired up. Then inserted the cdrom into the chain and the system once again booted properly. So far any way. The scanner is currently out of the chain and would be last in line with a centronics type terminator that plugs on the end of the cable and then onto the scanner. Could this length of external scsi units be too long?

Once this problem is sorted, the next step is to getting the warp'40 scsiII header to function...

Offline amiga92570

Re: A3000 external scsi termination
« Reply #1 on: July 18, 2007, 09:07:29 PM »
If you have an old WD33C93A -02, or - 04 SCSI chip it is not uncommon to experience random lockups with external scsi devices. Best to upgrade to WD33C93A - 08.
Amiga92570
==========================
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Offline T3000

Re: A3000 external scsi termination
« Reply #2 on: July 22, 2007, 04:48:57 PM »
Thanks for the reply amiga92570.
The WD scsi chip is version -08
There are no termination resitor packs on the MB
The 4gig drive is terminated on the drive
And currently there is only a CDrom and a 100mg zip drive on the external scsi chain with the zip being terminated with it's own termination switch. The scanner is out of the scsi chain but uses a passthrough centronics type terminator.

However, no one is able to answer any of the questions in the initial post?

Offline Boot_WB

Re: A3000 external scsi termination
« Reply #3 on: July 22, 2007, 05:38:29 PM »
Is the zip termination active or passive? Don't know, but it is probably active. The specsheet on the IOmega website does not specify which it is.

Would you need to terminate the zip on the end of the chain? Only if it is the last device. Whatever the last device is, this is what you need to terminate.

Is the scanner terminator add-on active or passive? Who knows - post some specs or a part number and someone will try to find out. Or just google it.

Is the length of scsi external units too long? I don't know, but in my experience there aren't any hard and fast rules, just general guidelines. If it works, great. If not, reconfigure and try again. :-)

Regarding your current issues I can see a couple of possibilities:

1) Perhaps the termination power is insufficient with so many devices attached. You could activate the TERMPWR jumper on your harddrive or you zip disk (probably a good idea anyway with so many devices attached.

2) Re-reading your original post, it sounds as if you haven't tried with just the scanner attached. Perhaps this will shed some light on the weak link in your scsi chain.

3) In post #3 you state that the scanner
Quote
uses a passthrough centronics type terminator

It sounds as if this is not a terminator - there is no reason for a terminator to have a pass-through, as by definition the terminator marks the end of the chain. Perhaps it is just a centronics <> d-sub adapter, or a male <> female adapter



Just to reiterate the obvious: TWO devices shall be terminated, and the number of devices terminated shall be ONLY two - no more, no less (five is way out, etc).

1) If you have only internal devices this should be:
a) The last device on you internal chain
and
b) EITHER the motherboard terminator packs OR a 25-pin terminator on the external SCSI port.

2) If you have only external devices (weird, but possible) this should be:
a) The last device on you internal chain
and
b) EITHER the motherboard terminator packs OR a 50-pin terminator on a cable attached to the internal SCSI port.

3) If you have internal AND external devices this should be:
a) The last device on you internal chain
and
b) The last device on your external scsi chain.

In any of these configurations any or all devices on the chain can supply additional TERMPWR if required.





EDIT: edited several times for clarity, to repair typos, and to answer all questions in order :-P
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Offline Zac67

Re: A3000 external scsi termination
« Reply #4 on: July 22, 2007, 06:02:11 PM »
There were lots of passthrough terminators around; when a device features only one port, you have little choice. However, terminating the bus like this should only be done when it's the only option. Make sure there's not another terminator inside the device; double termination doesn't work well.

BTW: When the terminator doesn't say 'active' it's passive.
 

Offline T3000

Re: A3000 external scsi termination
« Reply #5 on: July 22, 2007, 08:12:54 PM »
Heya Boot_WB. Thanks for the information.

Boot_WB --> Is the scanner terminator add-on active or passive? Who knows - post some specs or a part number and someone will try to find out. Or just google it.

There are no numbers/specs on this device. The terminator came with the scanner, bought new. Instructions (can't find the manual at the moment) indicated that the scanner is to have this terminator installed if the scsi chain is being used. The scanner is last inline as there is only one scsi port on the unit. There is also a parallel and a serial port on the scanner.

Boot_WB --> Is the length of scsi external units too long? I don't know, but in my experience there aren't any hard and fast rules, just general guidelines. If it works, great. If not, reconfigure and try again.

I'm using the shortest scsi cables that I can find. Also swapped cables, cdrom and zip drive around dozens of times. with the zip and cdrom and cables, the cahin is 6ft.  2ft cables and 1 foot each device.  Adding the scanner pushes the length to 9 feet.

Boot_WB --> Regarding your current issues I can see a couple of possibilities:

1) Perhaps the termination power is insufficient with so many devices attached. You could activate the TERMPWR jumper on your harddrive or you zip disk (probably a good idea anyway with so many devices attached.

Would have to tear the system down and check the HD. System works great without external devices attached and the external scsi port terminated with the block.

Boot_WB --> 2) Re-reading your original post, it sounds as if you haven't tried with just the scanner attached. Perhaps this will shed some light on the weak link in your scsi chain.

System works great with just the scanner on the external port.

Boot_WB --> It sounds as if this is not a terminator - there is no reason for a terminator to have a pass-through, as by definition the terminator marks the end of the chain. Perhaps it is just a centronics <> d-sub adapter, or a male <> female adapter

It is definetly a scsi terminator. It came with the scanner packaged in a bag labled scsi terminator.

Zac67--> Make sure there's not another terminator inside the device; double termination doesn't work well.
BTW: When the terminator doesn't say 'active' it's passive.

Terminator doesn't say anything.

Thanks for the input.
I'll be looking into the TERMPWR on the HD and try to locate even shorter scsi cables. For now I'll just have to swap out the cdrom/zip chain when I need to use the scanner. Also, this A3000 has a Warp engine in which I'll be eventually adding a scsiII drive to the warp scsi device. Will be hunting for an external scsi header and hopefully bypassing the stock A3000 scsi device all together.

Offline Boot_WB

Re: A3000 external scsi termination
« Reply #6 on: July 22, 2007, 08:31:26 PM »
Quote

Zac67 wrote:
There were lots of passthrough terminators around

@Zac67 Thanks - I didn't know that :-) SCSI always has something new to teach.

@T3000
BTW - The IOmega website suggests 5 feet as a maximum scsi chain length. Methinks they're being a bit cautious there.
Given the testing you've done it does sound like the cable length is probably the issue though. Do you have a spare 5.25" bay to install an internal scsi CD rom in your a3KT? might save you a vital few inches, even a foot.
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Offline Zac67

Re: A3000 external scsi termination
« Reply #7 on: July 22, 2007, 09:20:04 PM »
And yes: total cable length is limited to 6m (A3000 internal is SCSI-1), slightly more modern Fast SCSI (like on the WarpEngine) is limited to 3m.

The WarpEngine's SCSI is faster and - looking at the 53C710 - probably more reliable anyway, so I'd rather go that way. You can also split up the devices to avoid lenghty cables - but don't forget to change termination accordingly.
 

Offline T3000

Re: A3000 external scsi termination
« Reply #8 on: July 23, 2007, 06:11:35 AM »
Quote
Boot_WB wrote:
Given the testing you've done it does sound like the cable length is probably the issue though. Do you have a spare 5.25" bay to install an internal scsi CD rom in your a3KT? might save you a vital few inches, even a foot.


Unfortunately, the scsi problem is with my A3000 Desktop system. So there is no 5.25" bay to install an internal cdrom. The situation with my A3000T is far more severe than scsi problems...

Quote
Zac67 wrote:
And yes: total cable length is limited to 6m (A3000 internal is SCSI-1), slightly more modern Fast SCSI (like on the WarpEngine) is limited to 3m.


6 meters? that would be over 18 feet.  :-?

Offline Zac67

Re: A3000 external scsi termination
« Reply #9 on: July 23, 2007, 07:14:39 AM »
Well, the (crap Mac style) 25 pin port eats away some of the signal quality - I wouldn't exceed 3 or 4m and take care that only active terminators are present.