41CL Strange Behavior??

[Neve]

Hi all,

I reset my 41CL today (aka Memory Loss). I disabled the MMU (MMUDIS), and cleared it as well (MMUCLR).
This is when I noticed a very strange behavior. I don’t know if it’s normal, but, to me, it doesn’t seem to be.
Here is what I noticed:

When the MMU is disabled and nothing is plugged in to the calc, a CAT 2 responds perfectly. Same thing with a Card Reader plugged in —> Cat 2 is fine.

Now, when an HP-IL is plugged in (still with MMU disabled), CAT 2 returns a nasty and blurry “DATA ERROR”. See attached picture. At that point the HP41 freezes, and I have to remove to battery pack (not batteries, the rechargeable pack) to turn it off and reset it.

On the other hand, when the MMU is enabled (even with nothing virtually plugged in), everything works perfectly as they should. I mean that it works with no error just by enabling the MMU after a hard reset. This weird behavior doesn’t happen with a Card Reader plugged in. Just the HP-IL unit.

The unit works fine when the MMU is enabled, and it also works fine with my other 41CX unmodified machine. It also works perfectly with the PIL-BOX.

Is this normal?? Should I be worried?
If it’s not normal, how do I fix this issue?

Regards