990 vs 993 Remote Differences

the handhelds are the same.  the 993 does not have anything inside to upgrade,

The 993 base is essentially just a fancy looking battery charger.

Actually, this is not true.  I had to send my #993 back for the charger update.  After they replaced the charging circuit, it works flawlessly charging my remotes and they don't get hot like they do in the #990 command base.

Was it an actual update or a defective product repair?

(Our dehumidifier was getting warm to the touch and they said don't worry, after the case nearly melted they said there may be an issue with them but only a few, then they recalled millions of them from nearly every major store brand plus their own brand and required you to send in part of the cord. Seems they were catching on fire We are now a little edgy on "hot" running electrical equipment.)

Well, you can argue the semantics of update or defect, the bottom line is that to get the charger working properly, I had to send it back to Lionel.   The final "fix" for both my #990 and #993 was a new charging circuit.  They both charge properly now, but the #990 still gets the CAB2 pretty warm, so I just charge in the #993.

The reason you do not have to send the CAB-2 in for the update for versions less than 1.2 is that the register that had to be fixed was in the 990 base, there is nothing in the 993 base to repair, it is only a charger and not Legacy parts

I found out first hand when I bought v 1.1 993 set. I called to get an RMA and was told to just upgrade it. They recommend going 1.2, 1.3,1.5 but since I had no blue modules that I hadn't modified, I just went straight to 1.51 and haven't had any problems

I sent my 990 base back 2x for the charger, but the 993 charger has never been an issue. When we asked Lionel about the heat difference at the LUG meeting last year they said it was the Legacy electronics and not the charger that caused the heat. I monitored the heat last year and there is a substantial difference between the two

It obviously is the Legacy electronics that generates the heat, but the fact remains that the heat is there in the #990. 

My #993 would come up with the red light charge failure before it was repaired, now it will charge the remotes every time to a normal charge completion.  The repair order stated they installed a new charging circuit, which is what they did to the #990 as well.

All's well that ends well, I now have fully working Legacy remotes and chargers.

The 993 did not sell very well so there are a number of old ones

around that have V1.0 in the cab 2. The V1.0 Cab 2 will not

find a later version base so just update the Cab 2 to V1.52 and it

will find the later bases.

imo that is just splitting hairs.

I do not believe the op was asking that.

but more info can help others.