Frequency Standard

Description

I got this item on eBay.  It measures 7 5/16" x 2 3/4" x 4 9/16" tall.  On the bottom is a DB-25(m) connector and on the top there is an access screw to a trim pot.  Inside there are 4 double sided 6 5/8" x 2 1/4" printed circuit boards.

The top of the can has a date of 24 FEB 1994.

The A2 board says "Control Science Corporation"

Note:  When separating the boards it's possible for the socket pins to fall out.  Since all locations are not used it may be very difficult to get them back into the correct holes.

There are two kinds of pins for the Bendix connector, one type solders to the board and has a pin going down and a socket pointing up.  The other type solders to the board and has a pin going down but is short without any socket.  All installed pins make a connection to the PCB & Bendix connector below, but only some connect to the board above.

I've been told that this design includes anti reverse engineering elements and I think that's the case.  Normally after spending the time I've put into this the unit would be functional.  It's like how safes are rated to resist different levels of attack for different times or programming tricks that make reverse engineering harder.

Best Guess as to function

Based on the below observations I think this is an audio tone generator where the tone is selected by digital relay coil logic inputs to the DB-25 connector and the output is on one of the DB-25 pins.  With 11 relays there might be 10 or 11 different tones available.  Or maybe a binary sequence of tones where there are 2E11 possible tones?

The crystal is not ovenized so this is not a very high stability source, but a crystal would provide better stability than an RC type audio oscillator.  The adjustmet pot on the top board is not for triming the crystal which has it's own glass trimmer, unless the pot is for fine trimming and the glass cap is coarse tuning.

DB-25 pins 1 to 11 are relay coil -15 VDC inputs with 12 being the common +ground
DB-25 pins: 15, 17, 20, 21, 24 and 25 are power supply related.
DB-25 pins: 13, 14, 22 and 23 have no connection (nc).
DB-25 pins  16, 18 and 19 have an unknown function, at least one is an output

DB-25 pin 12 is the common for all the relay 1030 Ohm coils.  It takes 12 VDC to jsut trip the relay and abut 15 VDC for solid operation.  With a 1 k Ohm coil they pull about 15 ma.

Best Guess at powering up

The Logic supply appears to be + 7 VDC @ 270 ma on DB-25 pin # 24 and the ground return on DB-25 pin # 25.  This causes the yellow wire on the pass transistor to be at 5.2 VDC.

But the two model 1682 +/- 25 VDC converters are not getting any input, hence they don't have any output.
Maybe one of the 3 unknown pins is some type of enable that activates the +/- 25 VDC converters?

Level 0

The lower Aluminum plate that holds the DB-25 plug also has a metal box with three wires going to it, purple is ground and a purple not ground and yellow, most likely a power supply pass transistor.  There is a Bendix Scintilla 30 pin socket and all the printed circuit boards have a similar socket with both male and female connection so that they can be stacked.  The Bendix part number of this one is 10-299812-30.
 

Pin #	Wire Color	Function	Bendix Pin # all Up	Level 1 PCB
1	White	L4 Relay 500	7u
2	White	L4 Relay 498	8u
3	White	L4 Relay 502	29u
4	White	L4 Relay 497	10u
5	White	L4 Relay 499	16u
6	Blue	L4 Relay 501	14u
7	Blue	L4 Relay 496	17u
8	Blue	L4 Relay 495	12u
9	Blue	L3 Relay far from "A2"	3u
10	Gray	L3 Relay middle	2u
11	Gray	L3 Relay near  "A2" mark	19u
12	Brown	Com all Relay coils	20u
13	nc	nc	nc
14	nc	nc	nc
15	Red	+25 VDC test point	1u	1682 OUPT 1682 +25V
16	Purple	?	21u	L1 IC30 BB
17	Green	-25 VDC test pint	30u	1682 -25V
18	Yellow	?	25u	L1 IC31a
19	Yellow	?	23u	L1 IC31b
20	Black	op amp common	4u	1682 COM
21	Black	Case Ground level 1-2 shield level 3&4 can	nc
22	nc	nc	nc
23	nc	nc	nc
24	Purple	+7 VDC@ 270 ma in PS xistor term	9u
25	Purple	PS xistor case Power Supply  GROUND	11u	TTL IC  gnd
nc	Yellow	PS xistor term + 5.2 V main PS	24u	TTL IC +5V

Bendix connector has no pins in positions 5, 6, 13, 15, 18, 22, 26, 27 and 28.
All 3 erminals of the PS xixtor are floated from case ground.

Level 1

This lowest PCB contains a mix of ICs and discrete analog components.  On the bottom is a MDI Modular model 1682 DC to DC converter with markings, +in, -in, Trim, Oupt, -25V, Com, +25V.

The ICs on this baord are marked:
 

IC#	# Pins	Marked	Commercial
21	14	S8870A
22	14	S8280A
23	14	S8870A
24	14	S8280A
25	14	NA	544121n
26	14	S8280A
27	14	S8280A
28	14	S8826A
29	8 TO5	NA	52710L	op amp
30	8	BB
31	4	Blk Plastic box

Bendix Connector

Bendix Pin #	Description Up	Description Down
1ud	L4 DC module +25 out L1 DC module +25 out	"
2ud	L3 Relay middle	"
3ud	L3 Relay far from "A2"	"
4ud	L4 DC module common L1 DC module common op amp common	"
5ud
6ud
7ud-nc	L4 Relay 500 coil	"
8ud-nc	L4 Relay 498 coil	"
9ud
10ud-nc	L4 Relay 497 coil	"
11ud	"	L0 PS Gnd
12ud-nc	L4 Relay 495 coil	"
13	nc
14ud-nc	L4 Relay 501 coil	"
15	nc
16ud-nc	L4 Relay 499 coil	"
17ud-nc	L4 Relay 496 coil	"
18ud=23		L1 IC31b
19ud	L3 Relay near  "A2" mar"	"
20ud	L4 Relay Coil Common	"
21d=27	open	L1 IC30 BB
22ud	L1 module Output
23d=18	open	L1 IC31b
24ud	"	L0 + 5.2 V
25d=26	open	L1 IC31a
26ud=25		L1 IC31a
27ud=21		L1 IC30 BB
28ud
29ud-nc	L4 Relay 502 coil	"
30ud	L4 DC module -25 V out L1 DC module -25 V 0ut	"
31	nc

ud-nc means Up Down pin installed, but no connection on this level

Level 2

Between level 1 and level 2 is a thin fiberglass board with its ground shield connected by wire to ground.  The Level 2 PCB has a mix of 8 ICs and discrete analog components as well as a crystal marked 1M000000 (maybe 1 MHz).  Adjacent to the crystal is a glass variable capacitor.  There are 8 2N222 transistors each surrounded by a cap, 3 resistors and a diode.  and a couple of metal can op amps.

The ICs on this baord are marked:
 

IC #	# Pins	Marked	Commercial
1	14	S8480A
2	14	S8826A
3	14	S8488A ?
4	14	S8808A
5	14	S8826A
6	14	S8826A
7	14	S8826A
8	14	S8480A
9	14	S8480A
10	8 TO5	NA	52741AL	op amp

Bendix Connector

Bendix Pin #	Dexcription Up	Description Down
1ud	L4 DC module +25 out	"
2ud-nc	L3 Relay middle	"
3ud-nc	L3 Relay far from "A2"	"
4ud	L4 DC module common	"
5d	open
6d	open
7ud	L4 Relay 500 coil	"
8ud	L4 Relay 498 coil	"
9d	open
10ud	L4 Relay 497 coil	"
11d	open	L0 PS Gnd
12ud	L4 Relay 495 coil	"
13	nc
14ud	L4 Relay 501 coil	"
15	nc
16ud	L4 Relay 499 coil	"
17ud	L4 Relay 496 coil	"
18ud
19ud-nc	L3 Relay near  "A2" mark	"
20ud	L4 Relay Coil Common	"
21ud	L4 caps	"
22d	open
23ud	L4 resistors	L2 741 Out
24d	open	L0 + 5.2 V
25ud	L4 Main top Pot	"
26d	open
27d	open
28d	open
29ud	L4 Relay 502 coil	"
30ud	L4 DC module -25 V out	"
31	nc

Level 3 Board A2 CSC p/n C-005

Level 3 and Level 4 PCBs are enclosed in a metal shielding can.  The Level 3 PCB has 3 relays and a number of high Q capacitors, a couple of tublar caps marked .99 MFD 100 V.D.C and a couple of smaller ones marked 9100+/- 1% and others marked 91000+/- 1% and many more smaller ones.  Two glass piston trimmer caps also on the end of this board.

This board only has capacitors and relays, no active components.

The Relay coil common is Bendix pin #20 like on the level 4 board and the three coils are on Bendix pins 2,3 and 19

Bendix Pin #	Description Up	Description  Down
1ud-nc	L4 DC module +25 out	"
2d	open	L3 Relay middle
3d	open	L3 Relay far from "A2"
4ud	L4 DC module common	"
5	nc	nc
6	nc	nc
7ud-nc	L4 Relay 500 coil	"
8ud-nc	L4 Relay 498 coil	"
9d	open
10ud-nc	L4 Relay 497 coil	"
11d	open
12ud-nc	L4 Relay 495 coil	"
13d	open
14ud-nc	L4 Relay 501 coil	"
15d	open
16ud-nc	L4 Relay 499 coil	"
17ud-nc	L4 Relay 496 coil	"
18	nc	nc
19d	open	L3 Relay near  "A2" mark
20ud	L4 Relay Coil Common	"
21ud-nc	L4 caps	"
22	nc	nc
23ud-nc	L4 resistors	"
24ud	L4 caps	"
25ud-nc	L4 Main top Pot	"
26	nc	nc
27	nc	nc
28ud	L4 DC module + IN	"
29ud-nc	L4 Relay 502 coil	"
30ud-nc	L4 DC module -25 V out	"
31	nc	nc

ud-nc means no connection on this level

Level 4 Board A1 CSC p/n C-004

This is the top PCB that has the trimmer pot that can be accessed through the screw in the top outer cover.  There are 8 relays on this layer and by each one there are high Q caps.  It appears that the main purpose of this board is to switch caps.  A MDI Modular model 1682 DC to DC converter is also on this board, +in, -in, Trim, Output, -25V, Com, +25V are the labels. Another of these is on the lowest PCB.

There are no ICs on this board only 1 each RCA 2N2905 and RCA 2N2102 (connected as a diode) transistors.  The DC module -IN connection does not show up on the Bendix connector.

Bendix Pin # all down only	Description
1d	L4 DC module +25 out
2d	nc
3d	nc
4d	L4 DC module common
5d	nc
6d	nc
7d	L4 Relay 500 coil
8d	L4 Relay 498 coil
9d	nc
10d	L4Relay 497 coil
11d	nc
12d	L4 Relay 495 coil
13d	nc
14d	L4 Relay 501 coil
15d	nc
16d	L4 Relay 499 coil
17d	L4 Relay 496 coil
18d	nc
19d	nc
20d	L4 Relay Coil Common
21d	L4 caps
22d	nc
23d	L4 resistors
24d	L4 caps
25d	L4 Main top Pot
26d	nc
27d	nc
28d	L4 DC module + IN
29d	L4 Relay 502 coil
30d	L4 DC module -25 V out
31d	nc

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