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Posted Thu Sep 10, 2020 5:38 pm

I have a stock 25mhz A3000 with a fixed/updated WD scsi chip.

I have a question about the terminators on the motherboard. I have removed them to get my internal drive to work. Everything works fine when I have my internal drive and external DAT drive connected. However if I connect a second internal drive to the same ribbon cable, I often get hangs on the scsi bus. If I disconnect the DAT drive, everything returns to normal with the 2 internal drives.

Do the terminators on the MB terminate the internal or external SCSI bus?


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New Orleans, LA, USA

Posted Fri Sep 11, 2020 7:09 am

I am pretty sure both ends of a scsi chain need to be terminated, so that means you need to leave the terminator in place on the motherboard. The SCSI controller is the first end of the chain, and the very last drive in a linear chain from there will need termination.

In section 4-12 of the A3000 owner's manual, it says this:

"If both internal and external add-on SCSI devices are present, the termination resistor packs must be removed from the original hard disk for proper SCSI operation."

Also, make sure each device has its own unique SCSI ID, and keep in mind that the controller takes 7 and by default the first internal drive is set at ID 6.

There's more information in section 4-23 of the user manual.

EDIT: after re-reading the post, I believe you have a termination issue. There is an additional terminator somewhere that needs to be removed and then moved to the last physical device on each end of the chain. The last device on the external connector needs a terminator and the last device (think linearly -- the very last one on the ribbon cable) needs termination.

If you are using internals only, the terminator should stay on the motherboard OR you can take it off and place an external terminator on the external SCSI and a resistor pack terminator on the last internal device.

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Posted Fri Sep 11, 2020 1:41 pm

I think you may be right about termination. To further complicate matters the internal SCSI drives and DAT drive both have a jumper labelled "term power" which is vague at best. I don't want to double terminate of course.

I'll experiment to see if I can get it all working reliably. It works fine with DAT and ONE internal scsi drive, just not TWO internal scsi drives.

Thanks all!


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Posted Sun Sep 13, 2020 5:41 pm

Please share the model numbers of the drives (the two hard disk and the DAT drive). Also, the order in which the internal drives are connected - i.e. which one is closer to the motherboard connector and which one is at the end of the cable.

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