Problems installing Jessie to Powerbook from USB Stick

[Carlos <powerpc1990@gmail.com>]

Hello to all,

first of, great community. This is my first post but I have read a lot of threads on this mailing list. And I’m a totally noob on Linux.

I would like to install Debian from a USB-Stick, but sadly it fails. 

First off, my system requirements:

Apple PowerBook G4 1.5GHz
Model Identifier: PowerBook6,8 (February 2005)
Model Number: A1104
Boot-ROM Version: 4.9.0f0
OS: MacOS X v10.4.11


These steps I have done so far:

1. Downloaded Debian 8.8.0 non-free Firmware edition from here: https://cdimage.debian.org/cdimage/unofficial/non-free/cd-including-firmware/8.8.0+nonfree/powerpc/iso-cd/
2. I copied the ISO to USB-Stick with this command: 
sudo dd if=/Users/test/Downloads/firmware-8.8.0-powerpc-netinst.iso of=/dev/rdisk1 bs=1m

After I performed this command, I got:
308+1 records in
308+1 records out
323665920 bytes transferred in 27.002575 secs (11986484 bytes/sec)

And the stick appears in the Finder called „Debian/PowerPC_jessie (with lot of folders, e. g. install/yaboot)

The USB-Stick is shown in the disk utility as follows:
File system: MacOS standard (disk1s2)
Partition type: Apple_HFS (Apple partition scheme)

3. Booting the PowerBook in OpenFirmware
4. typed dev / ls and devalias

As described there: https://lists.debian.org/debian-powerpc/2012/08/msg00042.html

But I don’t find the USB-Stick. I also tried this command: „boot ud:,\\:tbxi“ as described there: http://ben-collins.blogspot.de/2010/08/booting-your-ibook-g4-from-usb-stick.html

But only it appears a no stopping sign.  I also have tried a different Stick. The first one with 2GB, the second with 8GB.

Could maybe someone give me a advice, please?

Thanks in advance
Carlos