So you're out there on the hunt for an older G-Shock, you find one at a decent price and receive it... only to find something odd--it doesn't function the way you expect it. It's been modded!
I know most of the mods talked about on the boards are cosmetic, with only a very few about swapping out modules. But most of the module swaps are done with 5600 and 5700 series.
In my search for an older MRG-220, I was lucky to have been outbid on an example that, unbeknownst to me had been modded.
Here's what was done:
The 1829 module that comes in the MRG-220 provides a city/location field, as well as a secondary time to swap between (the little square in the upper left will show "1" or "2"). The 1673 module doesn't have these functions, and includes a contact field and ID field, with time digits resting along the bottom. My watch is inset in the middle, which has the correct module.
Someone must have discovered that the MRG-200 and MRG-220 modules are a perfect swap, due to the shape of the module overlay. I prefer the 1829 module... although both of these have the horrible omission of a CDT! That really surprised me, given they were made in 1997 and 1998. For a top of the line MRG model no less.