Next level:

Thanks, Joerg

Now that didn't help a lot :/

At least it is obviously a "Fr" - that's a start.

I think I'll just crack open a CT and have a look at it, maybe it looks similar.

All CT based calculators I have as spares use a plastic casing, no lids, I didn't check the non-spare though. That would require a pro to chemically dissolve the casing.

(I have another idea - maybe I'll try to replace a Fr-chip by a CT-chip and see what happens. Not the easiest way...)

Hi.

Please, forgive me if I am trying to teach a prayer how to pray, but... If possible, measure the pin voltages and, if available, check the waveform (scopemeter or logic analyzer) on each pin prior to exchange one with the other.

Success!

Luiz (Brazil)