Assuming you are referring to the FW on the adapter board (i.e. U202), yes, I am certain I burned it correctly.
That's assuming the U202.bin file from the Ko4bb web site is good in the first place (just to check, the MD5 hash of the file I have is 79cebebdf156a9b1219a6c9f26da09e0).
Just to be on the safe side, I burned the FW once again, this time on a different 2732 IC.
I also bought an AT28C64B, burned it and tried with that.
In fact, I also burned the U222 FW again (on another 2732 IC).
I tried with these new ICs in their corresponding places, but the result is exactly the same.
Another thing I did was to order another batch of UB8840M, this time from a different seller.
I put in one of these newly arrived ICs but, as expected, the behaviour is the same.
In terms of shorts, I very much doubt it as I did both a visual inspection and continuity checks.
Also, I now have 3 boards that behave the same way, so it's unlikely I shorted them the same way.
To summarize:
1. The rest of the 8840A meter is working fine (confirmed with using an original Fluke CPU IC & associated U222 IC - true, those are FW 2.5, but I don't think that matters).
2. U222 IC (i.e. 2732 burned with corresponding U222 FW 2.3) is fine.
3. On the CPU adapter board:
3.1. UB8840M IC is good.
3.2. 2732 IC with U202 firmware is good.
3.3. I checked the adapter board connections are according to the schematics and it all checked out.
The only remaining parts which are left are really the 3 capacitors on the adapter board (I am using 1 x 10 uF electrolytic, 1 x 100 nF film and 1 x ceramic cap whose value I don't remember now, this last one on the 2732 IC power rail), but I doubt it they have any influence in this.
Any other suggestions, please?