B&W G3, YDL 4, no boot from hard drive after successful install

[EG]

I have a Blue & White G3, 400MHz, Rev. 2, with an Apple 2940 SCSI card
and a 9GB drive.

YDL 4.0 installed successfully as the only OS on this drive, no
dual-booting etc.  

However, after completing the install it will not boot into Linux on
its own.  I can boot YDL CD 1 and at the installer prompt do:

linux root=/dev/sda3

And it boots up fine.  BTW, I have also observed this same exact
behaviour on an IDE disk, removing the SCSI completely.  But now the
SCSI is back in the system and I'd like to know how to make it boot
into YDL.

I am an absolute novice at Mac hardware and Mac OS, but I have lots of
Linux experience.

After sifting thru a lot of the mailing list archives and Apple's site,
I am led to believe that it has something to do with Open Firmware,
yaboot, or perhaps ofboot.b.

The YDL installer offered to partition the disk with sda1 and sda2 for
the reserved Apple partitions and then:

sda3 /
sda4 extended
sda5 swap
sda6 /boot

Once I accepted this but then thought it strange that /boot be put in
an extended partition like that.  So on the most recent install, I
changed it so that /boot is just part of /:

sda3 /
sda4 extended
sda5 swap

The YDL installer successfully modified my OF boot-device to be:

/pci at 80000000/pci-bridge at d/ADPT,2940U2B at 4/@1:2,\\:tbxi

The SCSI disk is ID 1 and the sda2 partition has yaboot, so that seems
right to me.

However, the machine only boots into the little question mark icon
blinking in the middle of the screen.  I can hear the hard drive
clicking a little bit before this, like it is trying to boot.

After reading a bunch of various things about mac booting, I decided to
"zap the PRAM".  Now the boot-device is hd:,\\:tbxi -- obviously wrong
for my G3.  I've also tried pressing the CUDA switch with the power
unplugged.  (Not that I really know exactly how these could help, but
hey...)

So now I try to go:

boot /pci at 80000000/pci-bridge at d/ADPT,2940U2B at 4/@1:2,\\:tbxi

and OF responds with can't OPEN:
/pci at 80000000/pci-bridge at d/ADPT,2940U2B at 4/@1:2,\\:tbxi

Interestingly, if I run the command again a couple more times, the OF
prompt just hangs and I have to hit the reset button.

I'm hoping that someone can suggest a new thing to try in OF, or
perhaps shed some light on whether or not I need to modify yaboot.conf
or ofboot.b.

I have also tried running ybin -v (after booting via the CD), and it
appears to be working correctly, modifying the sda2 partition,
blessing, etc.

Thanks a lot for any help.

EG