I have a Tektronix 067-0589-00 Plug-In Extender for my 7000 series mainframes. I've used it on the Vertical Plug-ins over the years, but don't recall if I've ever tried it on the Time Base slot. I presently have no Internal Trigger from either Vertical Slots on my R7623A.
The Trigger Select Board that is mounted to the Interface PCB between the Right Vertical connector and that for the Time Base has a black Sharpie 'X' on the board. When I bought the mainframe at a TRW Swap Meet back in 2001, I never did a full check-out, so having just gotten the scope's -15V power supply back up and running, while getting burnt smell from someplace in the vicinity of the Interface board/Logic board (until the -15V supply woke up), I was finally getting the scope working. Only to find I don't have internal trigger from either vertical plug-in. Only with Ext Trigger do I get triggering.
Not sure if the Logic Board is involved in this, or it's just the Trigger Select Board that's in control of this. I do NOT have any signal appearing on the Sig Out BNC on the rear panel. Maybe the 155-0022-00 Trigger Select IC U324 on that board was already bad. All the semi's and resistors on that board measure fine.
I see in the Mains Interface schematic of the R7623A mainframe the balanced Trigger Select output feeds pins A20 and B20 of the Horizontal plugin connector so I was hoping I could check on the plugin extender for those signals.
Steven Selberg