Difficulty with flashing an HP20b

[mivok]

I had the same issue (with a 30b) and a mac. I was never able to get flashing working with the mac utility.

My solution was to use MySamBa (windows version) with wine. If you have homebrew (http://brew.sh) you can do 'brew install wine'. You also have to link your serial port to ~/.wine/dosdevices/com1 using something like 'ln -s /dev/tty.usb..... ~/.wine/dosdevices/com1' so com1 maps to your actual serial port.

In addition, I found I had to really press hard with the pins (resistors in the instructions you linked to) to make a connection, or it wouldn't work at all. You can tell when you're pressing hard enough because both lights (send and receive) on the ftdi cable light up (assuming you have send/receive LEDs).