[SunHELP] CD v NVRAM - what is happening?

[sunhelp at sunhelp.org]

I have developed a problem with external SCSI devices which is causing me 
much gnashing of teeth and wailing - especially since I need the external CD 
to load the OS onto a larger hard-disk.

System
------
SPARCStation IPX with external SCSI tape and external SCSI CD-ROM. Both have 
been running 100% correctly, first under Sun.OS.4 and lately RedHat Linux 6.2.

Recent changes
--------------
The only change made is a replacement NVRAM - which has all settings restored 
to the same as the original (to the best of my knowledge). Unfortunately this 
was done several months ago and I do not know if this was the cause - I 
haven't used the CD-ROM since then until now - but I HAVE used the tape with 
no problems.

Problem
-------
I am now unable to get data over the SCSI connection from the external SCSI 
CD, although no problem is apparent with the internal SCSI hard-disk.
The tape unit operates as expected, writing and reading data down the SCSI 
cable to and from the internal SCSI hard-disk.
The CD behaves as follows:-

Power up external SCSI devices.
    No activity - as expected.
Power up IPX.
    SCSI devices activate briefly as system checks them during POST.
Force to OpenBOOT monitor ok prompt
    probe-scsi - all SCSI devices report correctly (when connected!)
    boot cdrom - nothing happens, no CD activity, no boot,
        but.....
    boot disk - boots correctly.....
Into Linux as root....

dmesg shows the following boot-time messages:-

    various messages - no problems.....
scsi0 : Sparc ESP100A (NCR53C90A)
scsi : 1 host.
  Vendor: SEAGATE   Model: ST1480   SUN0424  Rev: 6266
  Type:   Direct-Access                      ANSI SCSI revision: 02
Detected scsi disk sda at scsi0, channel 0, id 3, lun 0
  Vendor: EXABYTE   Model: EXB-8200          Rev: 263H
  Type:   Sequential-Access                  ANSI SCSI revision: 01
  Vendor: SONY      Model: CD-ROM CDU-8012   Rev: 3.1d
  Type:   CD-ROM                             ANSI SCSI revision: 02
Detected scsi CD-ROM sr0 at scsi0, channel 0, id 6, lun 0
scsi : detected 1 SCSI cdrom 1 SCSI disk total.
Uniform CDROM driver Revision: 2.56
esp0: target 3 [period 200ns offset 15 5.00MHz synchronous SCSI]
SCSI device sda: hdwr sector= 512 bytes. Sectors= 843284 [411 MB] [0.4 GB]
    various messages - no problems.....
Detected scsi tape st0 at scsi0, channel 0, id 5, lun 0
    various messages - no problems.....

[disconnecting external SCSI prior to boot drops devices - as expected]

mount will NOT mount CD-ROM - reporting "no medium found"
but TCD 1.0.51 will happily read and play audio CDs.....
    .....whilst ignoring data CDs as one would expect.
Also, the caddy can be ejected by software.

Having attempted to mount a data CD, the following error messages are logged:-

kernel: sr0: CDROM not ready.  Make sure there is a disc in the drive.
kernel: cdrom: open failed.
kernel: sr0: CD-ROM error: Info fld=0x40, Current sr0 b:00: sense key Illegal 
Request
kernel: Additional sense indicates Illegal mode for this track
kernel: command was: Request Sense 00 00 00 10 00

Having attempted to play a data CD as audio, I get the following:-

kernel: CD-ROM I/O error: dev 0b:00, sector 64
kernel: isofs_read_super: bread failed, dev=0b:00, is o_blknum=16, block=32
kernel: sr0: CDROM (ioctl) reports ILLEGAL REQUEST.

Attempting to read directly from the drive as follows:-

    dd if=/dev/cdrom of/dev/null bs=512 (correct block size!)

.....produces nothing - not even drive-light activity.
This intimates that the kernel is not able to communicate with the device.
/dev/cdrom is linked to /dev/scd0 - both have read and write permission.

/etc/fstab has the appropriate entries for iso9660
The kernel is the correct version (ie the compile that used to work with the 
CD)
The compiled devices are as follows:-

Character devices:
  1 mem
  2 pty
  3 ttyp
  4 ttyS
  5 cua
  7 vcs
  9 st
 10 misc
 11 kbd
 14 sparcaudio
 29 fb
 36 netlink
128 ptm
136 pts
162 raw

Block devices:
  1 ramdisk
  2 fd
  8 sd
  9 md
 11 sr
 65 sd
 66 sd

.....and I presume sr is the CD-ROM, sr0, as shown during boot-up.

Also - the iso9660 filesystem was compiled correctly, /proc/filesystems looks 
like:-

        ext2
nodev   proc
nodev   nfs
        iso9660
nodev   devpts

.....which seems OK.

So - what the !*#~@ have I done wrong, and how do I extricate myself?
Some of the faq pointed me in useful directions (as you can see from above) 
but I am now banging my head against a wall!
N!k