............."As to the automation stuff...I was under the impression that JL Cooper had something to do with it, but the previous owner said this was a Tascam system. Maybe thats the difference between a 3500 and a 3700 automation........."
The 3500 had zero automation..just a blank area over there where the 10-key pad, floppy drive, lcd, scroll wheel etc are on a 3700.
You mentioned that the front face plate of your mixer says Tascam M-3500. Take a look at the serial # sticker on the back of the console just above where the power supply umbilical cord plugs in. That says 3700, right?
Back in the old days where one could buy the extended meter bridge, the extension came with a new plastic translucent front cover that covers all the meters. It's the plastic cover itself that has the silkscreen printing on it that says "Tascam M-**** and also the printing for the switches (Aux, group, tape etc).
Since the extended meter bridge kits were available for 3500s and the later 3700's, I bet what's happened is that an owner bought an extended meter kit for the 3700 (since it was not stock with the console) and either ordered incorrectly...or was shipped the wrong version....Receiving the kit for a 3500...which would only be different from a 3700 kit in the silkscreen printing only.
Back to the automation............
The stock 3700 came with dynamic or snapshot automation (you open the little hinge door behind the lcd and flip the dip switches to choose which kind of automation you want..plus a few other settings regarding frame rate etc). The entire use of stock automation is from the console channel vca controls and the right side master automation area. The only way to save a mix on the stock console is via the 3.5" floppy drive.
JL Cooper designed and invented that stock automation system for Tascam. Then JL Cooper went a little further by offering their own, $1000, separate "hot-rodded" add-on kit that would substantially increase the 3700 automation's capability.
The add on kit consisted of a manual, software to run on an external Mac, and a circuit card that inserts into the 3700 (it was user installed, fitted under the lcd...you notice the entire lcd/10-key/scroll wheel area is mounted in a panel. Unscrew the screws to that panel, the entire panel lifts up, revealing the area where the optional JL Cooper card snapped in).
Once powering up the 3700, you had a choice of running the automation in stock mode, or in the hot-rod JL Cooper mode, via dip switch setting.
I installed the option on both 3700s. The additional capability with the hot rod add-on includes being able to tweak your automation in real time via a Mac hooked up to the console. Making it very easy and visual to update mixes ..rather than using the various vca "update" switches/faders. Auto-fade was built in to the software. You could set up any fader as a group master via the Mac...substantially increasing the number of available groups. You could name each fader on the Mac screen for easy reference. You could save your automation mixes on the Mac hard drive, eliminating the need to use the 3700 floppy drive. All pretty cool stuff back in the day. Plus it was pretty cool to hear your mix going by while watching all the faders on the Mac screen bounce around.....almost like having a full daw back there in 1992.