HP 41C Video interface test. Howto?

[tribidouille]

Well, to sum it up,
-The video converter sends an image to the TV, clear enough, full of triangles.
-The problem of this 82163 seems to be in the HP-IL communication part of it.
-The tests Sylvain kindly posted show the HP-IL is working (empty closed loop is ok) but printer is not detected by the 41: flag 55 and 21 are "NO".

I should try to find schematics to understand where to investigate further.