Nicolet 526

The Nicolet 526 is a signal averager that is used in a modified OEMed Tektronix 5110 (5103N/D10) mainframe. The modifications to the mainframe performed by Nicolet include

adding a perforated panel for fan cooling via the bottom panel of the scope,
adding a 12-pin connector on the rear panel of the scope
connected the 12-pin connector to the interface board, connector J604.

The 526 has its own +5V regulated rail. An external source of +7V unregulated DC is routed from thee 12-pin rear connector to the mainframe interface board, and into the plug-in. An LM323 +5V three-terminal regulator is the source of the +5V rail within the Nicolet 526. (Even though the input is marked "+7 UNREG" on the board, it should probably be +7.5V minimum, per the LM323 datasheet.) Since the LM323 is rated for 3 amperes, it is unlikely that the plug-in sinks more than that from the "+7 UNREG" input.

How does the Nicolet 526 get the horizontal signal to the scope if it only plugs into the right vertical plug-in interface connector? In a standard, unmodified 5103, there is no signal path from the right vertical connector to the horizontal amplifier.

Mechanically, the Nicolet 526 is a three-bay 5000-series plug-in. It mates with the center-bay plug-in connector. The Nicolet 526 is made of four boards and a backplane which has a 40 position two sided edge connector for each board. Connection to the Tektronix mainframe is done via the backplane. The four boards are:

ADC and Register: The SIGNAL wire from pin 23A on the plug-in interface goes to the inverting input of an LM301 opamp via a resistance of around 165 kΩ. The noninverting input of this opamp is grounded.
Address
Control
Memory

The design makes heavy use of 7400-series digital logic in DIP packages. The printed circuit boards are two-layer. The memory is an array of Fairchild 2102DC MOS 1k x 1 static RAM ICs, DIP, soldered in place.

The wires connecting the backplane board on the 526 to the mainframe interface connector on the 526 are labeled:

H LOCK TRIG (white w/ black stripe), pin 27B of the plug-in connector
TRIGGER (light violet) 26A
RO TRIG (violet) 26B
Y LOCK IN (blue) 25B
FID SIG (green) maybe "FID" stands for "Free Induction Decay" in NMR? pin 24B on the interface connector, wired to pin 33 of the board #2 (address).
SIGNAL (brown) 23A
RO STUS (yellow) 23B
+7 UNREG (black), pin 22A and 22B of the plug-in connector
+7 UNREG (black), pin 22A and 22B of the plug-in connector
GND (white) 14A and 14B (standard 5000-series pinout)
GND (white) 14A and 14B (standard 5000-series pinout)
-VERT SIG (white w/ red stripe) 13B (standard 5000-series pinout for vert CH2)
+VERT SIG (white w/ brown stripe) 13A (standard 5000-series pinout for vert CH2)
-HORIZ SIG (white w/ orange stripe) 11B
+30 (red) 5A (standard 5000-series pinout)
-30 (orange) 5B (standard 5000-series pinout)
11A is jumpered to 14B at the male plug-in connector of the 526.