Weird SCSI problem!

[Gurm]

Ok folks,

This is the oddest thing EVER.

I have an Adaptec 2940UW. For plugs, it has an internal 50, an internal 68, and an external 68.

On the internal side, I'm running my DVD drive (a Toshiba SD-M1201) and my burner (which WAS a Ricoh 7060S, and is now a Plextor PX-W124TS). Both are on the 50-pin ribbon.

On the external side, I'm running my scanner (HP ScanJet 4p) and my Zip 250. This is accomplished by an active 68->50 converter plug, into which an HD50->Centronics cable is plugged. This runs to the scanner. I run out of the scanner with DB25->DB25 into the Zip, which is terminated.

Here's the problem... when I upgraded to the Plextor drive, I started getting intermittent problems with it. The first drive was definitely 100% defective, but this new one isn't. It works fine... but ONLY when the external chain is disconnected!

How weird is that? There's no overlap of SCSI ID's, and it doesn't make any difference how the drives inside are arranged or terminated.

If I plug in the external chain, the burner just doesn't work.

Well, a caveat - it burns. It just doesn't READ. How unbelievably odd is that?

Any ideas? I haven't begun to check the settings yet, and I also haven't tried an active terminator on the internal chain. Anyone think these might make a difference?

Also, it's not the SCSI card, I swapped it for another one just like it and it's fine.

And remember - my Yamaha 4x and Ricoh 6x burners both worked flawlessly on this exact rig.

- Gurm

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Listen up, you primitive screwheads! See this? This is my BOOMSTICK! Etc. etc.

[dZeus]

I think i have read about this:

because of the 68 -> 50 convertor, and the 50 -> 25 pin convertor, de SCSI bus is not properly terminated any more...

My advice is to put all the external non-68pin SCSI devices on a separate controller which has a 50 pin external connector

[Gurm]

So why is it only manifesting when the faster CD burner is installed? I understand the concept, it's one of the reasons the 2940UW Pro was introduced (it had completely reworked termination circuity).

Is it because the faster burner requires better termination, etc.?

I _might_ be able to get another SCSI card... in fact I have an ISA one here somewhere... hmm...

- Gurm

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Listen up, you primitive screwheads! See this? This is my BOOMSTICK! Etc. etc.

[Brian R.]

Sorry Gurm, I can't answer your question, but I have a similar setup and I have no terminator on the external chain. Also, I use a cable with a 68-pin socket on one end and a 50-pin socket on the other for the scanner. Works fine (at least it's stable. Maybe you can try that.

[This message has been edited by Brian R. (edited 08 June 2000).]

[Gurm]

Yeah I'm gonna try it both ways. I had feared at one point that I would have problems going SCSI3->SCSI2 then SCSI2(db50)->SCSI1(Cent50) then SCSI1(db25)->SCSI1(db25) then terminating. Prolly not enough juice on the line at that point. Maybe I'll try an active terminator and see if that helps, but it prolly won't since it's a (db25) connection.

It might help to get a cable that's (HD68)->(Cent50) or (HD68)->(db25), but it might not, too.

Worse comes to worst, I've got an ol' ISA SCSI card, and an empty ISA slot.

- Gurm

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Listen up, you primitive screwheads! See this? This is my BOOMSTICK! Etc. etc.

[SCompRacer]

I had a similar problem when I installed a Plextor CD ROM drive with a scanner installed on the external connector, a P2B-LS with onboard SCSI. I was using an Adaptec 68 to 50 pin adapter that terminated the high byte of the external wide connector.

Turned out I needed to install an Active terminator on the scanner. Most all ship with passive one. Plextor finally told me that months after I sent both drives back and called them by chance. Other drives are fat dumb and happy with passive termination, but not Plextor's.

I see you have your ZIP 250 at the end of the chain so my question would be is that active termination or passive? I would guess active but it's worth finding out.

[Gurm]

Ha ha, active termination on a Zip drive? You must be mad! Actually I think that Jaz drives do have active, but this zip is most certainly passive. I'll try that first, it would certainly save me putting in this shitty extra ISA SCSI card.

- Gurm

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Listen up, you primitive screwheads! See this? This is my BOOMSTICK! Etc. etc.

[SCompRacer]

Nope, I never knew what kind of termination was enabled when you flipped the switch on the ZIP.

Your problem should be solved with active.

[The PIT]

It would be useful if manufacters told you what type.

[SCompRacer]

I agree with The PIT. When I called UMAX to ask them about what type of termination they shipped with scanner, was on hold for quite a while till he got an answer that it was Passive. Then I knew I had to spend the bucks for the Active one.

[Gurm]

'Course I have to make the problem worse to make it better...

Nobody carries active terminators for DB25, so... I'm running...

HD68->HD50 (adapter)
HD50->db25 (cable to zip)
db25->db25 (cable to scanner)
cent50->HD50 (adapter on second scanner plug)
HD50->TERM (active HD50 terminator)

*sigh*

Wish me luck.

- Gurm

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Listen up, you primitive screwheads! See this? This is my BOOMSTICK! Etc. etc.

[Scytale]

I just did

[Brian R.]

Gurm - A couple of comments:
Is it recommended that your zip be the last drive on the chain? Some external removables are like that.

Is your external chain too long? Sometimes this is an issue, depending on the cable quality. You may be shorter than the maximum allowable, but if one of the cables is of lesser quality...

Are your cables of high quality? I've heard of people having trouble with a cheap cable anywhere in their external chain.

Brian

[This message has been edited by Brian R. (edited 10 June 2000).]

[Taz]

I know this is kind of obvious but have you turned termination off in the Adaptec's BIOS?

[SCompRacer]

My bet is still on termination.

Passive termination simply provides impedance close to the impedance of the cable and it relies on the interface card to provide steady power.

Active Terminators control the impedance at the end of the SCSI bus by using a voltage regulator, not just the power supplied by the interface card.

Without active termination on my scanner, the Plextor would be erratic in operation.