Model 8500 Controller diagnostics

We have a few old-model 8500 servo-hydraulic controllers and 1331 load frames. Generally, they work just fine, but occasionally a card within the 8500 tower will throw a fault and stop operating. Instron discontinued the machine long ago, and diagnostic/service documentation was never available to end users. I've had some occasional success making repairs when this happens, but I've also been very lucky. Except until now.  System won'tr pass self test, and hangs on "step 3".  Anybody out there ever work on one of these? Any idea how to talk to the 9-pin "diagnostic ports" on the cards to figure out what the "red light #1" fault actually means. Anybody know what happens on the different steps of the 6-5-4-3-2-1 self-test countdown? Anything?