CLI 5476 with 2720 -9406 compatibility

Hello,

I recently acquired a 9406-170 with a 2720 twinax controller and am
attempting to use it with a CLI 5476 terminal, but no success with the
terminal connectivity.

IPL (01 A M - M as in Mary) shows C6004031 on the front panel after a few
minutes. A little while later the amber LED lights up and another result
appears on the panel and some searching indicates the server gave up trying
to reach the console. The console cursor stays in the upper right corner
and never moves. If I use "01 A N" the machine appears to boot properly
(takes about a half hour for the disks to settle down). I use the white
power button to perform a graceful shutdown (I've never yanked the power
cord).

I have tried 2 4-port twinax blocks, one IBM and one Perle, connected to
the DB9 on the 2720 using RJ45 baluns. I pressed and held the spacebar
while powering on the terminal and set it to use address 0 with 3476
compatibility.

Is the CLI 5476 supported with the 2720 controller? Maybe i'm trying to do
something that will never work but i've run out of ideas to troubleshoot
the issue.

Any help would be greatly appreciated.