A Trimble 5000A timer by another name?

[foxops]

I've got a unit that might be relevant to those interested in early Trimble hardware: an "FTS 8400 Satellite Timing Receiver," rebadged by Frequency and Time Systems, Inc. (Beverly, MA) — an atomic frequency standards company later absorbed into Datum/Symmetricom/Microsemi/Microchip.




It has the same front panel layout as the Trimble 4000SX, but powder coated instead of brushed aluminum - and FTS branded. The guts seem to be a mix of Trimble boards for GPS and FTS hardware for the rubidium oscillator and clock distribution.



Three primary boards of interest:
11457-00 REV D "SIXTEEN BIT PROCESSOR"
10882 REV E "CLOCK BOARD"
11236 REV C "CHNL/4000S"



The EPROMs have stickers over the windows with "5000A+ / REV 2.00" printed on them - which as far as I can tell references the Trimble 5000A Timer. I haven't been able to find a manual, schematic, or even a photo of a 5000A anywhere, so if this is genuinely 5000A lineage firmware sitting inside an OEM chassis, it might be one of very few surviving examples.

I have high level photos and full ROM dumps if anyone wants to dig into the firmware or compare part numbers. Would love to know if anyone recognizes the 5000A lineage specifically, or has run across other OEM-rebadged 4000-series units from this same window (1985-87). I feel like I should be building a museum around this thing, but for now the best I can do is this handcrafted html:

https://sdf.org/~sjj/fts_8400.html

I'd like to get it into an operational state, so reverse engineering the firmware is gonna have to happen in order to address the GPS rollover bug (and maybe WGS72 related problems?), as well as component level testing before powerup. I'd welcome any suggestions on the matter, and will update the placeholder site with any progress.

[foxops]

ROMs dumped and merged. The smaller bank seems to contain bootstrapping for a virtual machine, the bytecode of which is found in the larger bank. I would have expected such an instrument to have firmware made obtuse by dirty optimization tricks focused on speed, but it seems like they were more worried about ROM space...