Can't get Quadra 650 SCSI set up.

[trag]

As long as the terminator is within (IIRC) 3" of the end of the cable it is within specification. So a passthrough terminator right before the SCA adapter will be fine, provided that the SCA adapter/hard drive.

Depending on the cost of a pass-through terminator, consider getting a good SCA adapter, which can provide termination, instead:

http://www.ebay.com/itm/111035026224?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

Then all you need is the SCA adapter, and no additional pass-through terminator.

I'd really like to find a SCA adapter like the one I just listed for less than $10. There's not that much difference in component count between it and the $3 ones, but for some reason, the ones which can actually let you configure your SCSI chain properly cost seven times as much.

"Single-Ended" has nothing to do with termination. SCSI went through several versions, starting with just SCSI, then SCSI-2, which included the enhancement Fast SCSI-2, then Ultra-SCSI. After Ultra-SCSI, came Ultra2-SCSI and everything was LVD SCSI, which stands for Low Voltage Differential.

Everything which is not LVD SCSI is Single-Ended (SE) SCSI. Only, we never called it that, because we didn't really need a special name for it, until LVD became common. Until LVD came along there was nothing to distinguish early SCSI from (except early differential SCSI of HVD SCSI, but everyone has happily forgotten about that).

The reason why SCSI is separated into early SE SCSI and later LVD SCSI is because the analog method of sending the digital signals changed. In single ended SCSI each signal just has one wire. The electronics compare that wire against GND and determine whether it is low or high (0 or 1). But low and high are kind murky. Low might be anything under 2V. High might be anything over 3V. The range in between might be uncertain, or different for each wire.

In low voltage differential SCSI, each signal has two wires. For a 1 one wire is high and the other low. For a 0 the previous situation is reversed. There is no GND, which just sits at 0 all the time, involved in the signal. The electronics have a much easier time comparing these two wires, and just deciding which is higher in order to determine 0 or 1.

So old SCSI is Single Ended. Only 1 wire changes to indicate the data value. Newer SCSI is differential. Two wires are compared (the difference is found) and their relative state determines the value of the data. Newer SCSI is usually built so that it is capable of using the old signaling method. The second wire for each signal just becomes a GND wire and the signal wire is interpreted the old way.

Newer SCSI is also called "low voltage" because it uses a lower signaling voltage for its differential signals than the older and mostly forgotten, original differential SCSI. If we had never had old differential SCSI we'd probably just call the new stuff "differential" and leave off the LV.

There's a wealth of information here: http://www.scsifaq.org Or, there used to be. I haven't read the site in a long time to see if it is still good. But these old UseNet derived FAQ sites don't usually change much.

Strangely, the Wikipedia article doesn't reference it. But then the Wiki article gets a few other things about SCSI wrong too.

 

[KieranD212]

I ended up buying a 50 pin passthrough terminator, it worked out cheaper. Well just got to wait now, I've retrobrite by keyboard and adb mouse so i might do the case next while its not in use. I used creme peroxide to do the "retrobrite".

 

[tecneeq]

How does one harvest UV radiation during this time of year in the UK? :lol:

 

[KieranD212]

Hehe yeah we're known for dull weather. The peroxide doesn't dry out because its not hot, but theres plenty of light recently between the rain lol. Since it doesn't dry out easily i can leave items out longer.

 

[KieranD212]

I'm really annoyed with this, the 50 pin pass through terminator i bought came in the mail today and so i installed it. It does F**K all! Really i have no idea why this thing wont boot from CD now. The HDD not being apple or formatted at the moment should not be a problem for the CD drive to boot.

What next?

EDIT: Okay so i'm thinking it has to be the SCSI cable itself. I swapped the hard drive and cd drive around, just the same. I can't have them set up that way as they don't fit in the case like that, HDD cage is on top of the CD drive.

 

[KieranD212]

If i make sure the last and first device are terminated could i leave a connector free (no device)? or am i better to buy a 2 device cable for the HDD and CD Drive. I know the first connection is to the mobo and its already terminated.

 

[trag]

It's fine to leave empty connectors on the cable. Leave middle connectors empty. Always have terminated devices on the connectors at the two ends.

If I was you, I would try just the CDROM drive with the pass-through terminator on the last connector on the cable. See if you can boot at all. Once you get that working, you can look at adding the hard drive into the mix.

 

[KieranD212]

Battery was not burst, but it was rusted and dead so i took it out; glad i found it so no damage can be done. STILL I HAVE NO IDEA about why it wont boot from CD. My drive ejects but doesn't read discs.

Ive tried just the passthrough adapter on one end, tried a brand new cable. Bought a new CPC Lithium battery on ebay, 1/2 AA 3.6v so waiting for that to arrive.

Im going to try the cable again just to make sure, but im only getting the flashing ? logo unless i use a disk.

I held the key combo to boot from a specific SCSI ID and it did nothing.

 

[KieranD212]

Okay the new battery i dont even know if it did anything but its fitted.

Thanks for all the help guys i appreciate it, but i think im going to give up on this. The only things left i think are to get a new CD drive or try another terminator and SCSI cable with only the terminator at the end.

 

[KieranD212]

I need a boot disk image that has CD drivers so i can test to see if the CD Drive is working. The Macintosh might not even be able to boot from CD at startup, this is why i need a floppy to test.

 

[KieranD212]

Better late than never. Finally got it set up, i just installed OS 8.1 because it was easier than 7.6.

What happened is that i bought a Macintosh Classic II and a 500gb Apple hard drive 25 pin ect, never used it in the Classic II so i stuck it in the Quadra 650.

LOL first time i booted the CD i got 7 drives because it thinks i had set 7 scsi devices, so i had to go back and change the jumpers. The CD drive works perfect so it must have been a SCSI problem with termination with the 80pin drive.