Conference 7.286::atarist

1287.0. "SCSI bus locks up after replacement of drive" by BERN01::RUGGIERO (Markus from Switzerland) Wed May 27 1992 04:19

    Friends, I have a problem!

    In my MegaST I have a DEC RZ23 disk with SCSI address 0. The SCSI
    adaptor is a german product (LACOM LAADAP2). I also have a SQ550 44MB
    removeable cartdrige drive. This is on the same SCSI bus on address 1.
    Everything worked fine until I had to replace the SQ550 (badly mounted
    head, replacement under warranty).

    Now I have a new SQ550. Hooked it up to the bus (address set to 1!) and
    tried to boot...

    There seams to be a serious problem on the SCSI bus. The system
    sometimes boots from the RZ23 but does not recognize the SQ550,
    sometimes comes up with both devices, sometimes with none or crashes
    during boot and loops between reset and boot.

    Yes, I checked bus termination (the RZ is terminated as it is the last
    device on the bus, and btw I did not change anything, just replaced the
    SQ!!)

    Somehow I managed to boot from the RZ. Various SCSI tools (the one that
    came with the SCSI adaptor and others) can see both devices but as
    soon as I make a disk access to one of them, the bus locks up, the busy
    LED on the RZ goes on (description of how to add this LED is somewhere
    in this notesfile) and stays on. Bus locked, Atari complaining about
    "output device does not respond".

    Has anyone seen this sort of problem? Remember I only replaced a faulty
    SQ550 with a (apparently not so) similar newer mechanism.

    HELP

    Thanks

    ---markus---

1 - Be sure you are only terminating the bus once - make sure the
terminators are removed from the Syquest drive.

2 - Do you have instructions on the Syquest jumpers?  Is it set to
ignore parity?

I don't have a Syquest, but these are things that come to mind with
other SCSI things I have done.

    Last night I found the time to investigate further...

    I can get everything to work perfectly when I set the SQ555 to SCSI
    address 0 and the RZ23 to 1 but not the other way round. This used to
    work with the old SQ555. I now can not any longer boot from the RZ23
    and use the SQ555 for backup and scratch purposes.

    No problem with bus termination or cables. Just changing the jumpers
    for the address on both mechanisms and the problem is there.

    And still: both drives work perfectly well with address 0 when
    connected to the bus only one at a time.

    To me it looks as if the RZ23 tries to be owner of the bus when it is
    the boot device - but this did not happen with the old SQ555 before
    replacement thus being an indication that it is NOT the RZ23
    that causes the trouble.

    Darn strange...

    Any ideas out there???

    ---markus---