Frequency Standard

FSN 6625-00-165-5773
1549-4010-A546-A
RANAD
U.S. Army Part No 1115/116
©Brooke Clarke, N6GCE


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.

Audio Frequency Standard
Audio Frequency Standard


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.
Audio Frequency Standard
Audio Frequency Standard

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.

Audio Frequency Standard
Audio Frequency Standard


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.
Audio Frequency Standard

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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