This page is devoted to the electrical and mechanical aspects of the AGC and DSKY, and perhaps eventually to electrical and mechanical aspects of the entire G&N (guidance and navigation) system.

This is an ongoing effort.  The long-range goal — or perhaps "wish" is a more-accurate term — is to provide the following engineering resources:

  1. The complete set of engineering drawings (electrical schematics and mechanical drawings) for AGC/DSKY and other G&N components, in all revisions, in the form of scanned images of the original Apollo Program drawings.
  2. Contemporary Apollo Program theory-of-operation documents for the above.
  3. Electrically and visually accurate transcriptions of those electrical schematics into a modern open-source electrical CAD program.
  4. Accurate translation of mechanical drawings of fabricated parts into reusable 3D models.
  5. Translation of AGC electrical design into Verilog hardware-description language or other standardized languages when appropriate.
  6. Simulation of the AGC hardware, via modern open-source Verilog-simulation software, or other software when appropriate.

Great strides have been made toward the goal, but it nevertheless remains very distant.

Search or Browse the Available G&N Engineering Drawings by Drawing Number or Title

Searching by drawing title is a relatively unrewarding activity, because so many of the drawings have such similar titles ... i.e., there are usually lots of matches.  Nevertheless, I have set up a little search engine you can use that might help, and it will search for drawing numbers as well:

Go to the engineering-drawing title search-engine page

On the other hand, if you want to browse through the drawings by number, rather than searching, keep reading! 

In the table below, "Miscellaneous drawings" refers to alternate scans of some of the drawings in some of the "boxes" in the table, as well as various drawings (or revisions) that aren't in the boxes at all.  Therefore, to find any given drawing, by number/revision, look in the box that covers that drawing-number range first, and then consult the miscellaneous drawings if what you want is missing from the box or is illegible.

Box 431, 102010-1000275 Box 432, 1000283-1002237
Box 433, 1002240-1002323
Box 434, 1002323-1002325
Box 435, 1002325-1002349
Box 436, 1002349-1003081
Box 437, 1003082-1003733
Box 438, 1003733-1005799
Box 439, 1006002-1006898
Box 440, 1006904-1007131
Box 441, 1007141-1007547
Box 442, 1007548-1008271
Box 443, 1008283-1010253
Box 444, 1010254-1010493
Box 445, 1010494-1011399
Box 446, 1011400-1014219
Box 447, 1014221-1014999
Box 448, 1015000-1015739
Box 449, 1015740-1016118
Box 450, 1016122-1019690
Box 451, 1019691-1021200
Box 452, 1021200-1897187
Box 453, 1897190-1900098
Box 454, 1900100-1900712
Box 455, 1900713-1900943
Box 456, 1900943-1901695
Box 457, 1901700-1902397
Box 458, 1902404-2003120
Box 459, 2003121-2005061 Box 460, 2005062-2007114
Box 461, 2007115-2007239 Box 462, 2007240-2010084
Box 463, 2010085-2012508
Box 464, 2012509-2014643
Box 465, 2014644-2015500
Box 466, 2015502-2018632
Box 467, 2018634-2021670
Box 468, 2021971-2900541
Box 469, 2900542-2901129
Box 470, 2901143-6010677
Box 471, 6010678-6015000
Box 472, 6015000-8106098
Box 473, JDC0001-JDC04390
Box 474, JDC4409-JDC10709
Box 475, JDC10710-JDC12621
Box 476, JDC12622-JDC18874
Box 477, JDC19021-MC25922

Miscellaneous drawings

Browse the Available Engineering Drawings by G&N System Component

If you know what guidance-system component (AGC, DSKY, etc.) you want the drawings for, this is the right place!

Various models of the Guidance&Navigation (G&N) system components such as the AGC and DSKY were designed and built during the evolution of the Apollo program.  Those components were then installed into G&N systems (or used for other purposes), and the G&N systems themselves were in turn installed into spacecraft or used for other purposes. The following table allows you to access the engineering-drawing trees for some of those G&N system components.  Beware, though, because there are gaps in the coverage!  In no case is the drawing tree for any given component model 100% complete.  On there other hand, there is so much overlap between these different models, there's little doubt that with some judicious engineering you could nevertheless construct most of these models rather faithfully from the drawings we do have.  With some exceptions, AGC/DSKY models or other components never installed into G&N systems aren't referenced in the table; nor are individual components or minor assemblies.  Moreover, there are additional G&N system components that I haven't been moved to add to the table below. But those additional items, where available, can still be accessed from the numerical drawing indices in the preceding section once you know the drawing numbers for them.

G&N System
G&N System Number
(Spacecraft, Mission)

CDU [4]
Block I CM Systems (Installation list 1014999)
1003186 MD2
1003458 MD1
1003459 MD2
1003469-011 MD1
1003458 MD1
1003495-011 [1]
1003524 MD1
1003553-011 [1] 1015500-011
1003700-011 1003524 MD1 1003540 MD1 1015500-011
-041 12
1003706-051 [2] 1003563-051
17 (CSM-011, AS-202)
1003564-021 [3]
-061 20
1003564-011 [3] 1015500-021
-071 109
1003700-051 1003706-031
-081 110 (Qualification system)
1003577-021 [2] 1003563-041 [3] n/a
-091 111 (Qualification system)
1003700-051 1003706-031
-101 121
1003700-051 1003706-051 [2] 1003563-051 n/a
-111 122 (CMO-17, Apollo 4)
1003700-051 1003706-051 [2] 1003563-051 n/a
-121 123 (CMO-20, Apollo 6)
1003700-071 1003706-051 [2] 1003563-051 n/a
Block II CM Systems (Installation list 2014999)
-021 202 (CSM-098, 2TV-1)
2003100-061 2003950-061 [2] 2010744-091
-041 204 (CSM-101, Apollo 7)
-051 205 (CSM-116, Skylab 2)
2003993-111 [2] 2003994-121
-061 206 (CSM-106, Apollo 10)
-071 207
-081 208 (CSM-103, Apollo 8)
-091 209 (CSM-104, Apollo 9)
-101 210 (CSM-107, Apollo 11)
-111 211 (CSM-108, Apollo 12)
2003993-031 2003994-121 2007222-231
-121 212 (CSM-109, Apollo 13)
2003994-121 2007222-231
-131 213 (CSM-119, Skylab
Rescue / ASTP Backup)
2003993-031 2003994-121 2007222-231
-141 214 (CSM-110, Apollo 14)
2003993-111 [2] 2003994-121 2007222-181
-151 215 (CSM-111, ASTP)
2003993-111 [2] 2003994-121 2007222-231
-161 216 (CSM-113, Apollo 16)
2003993-071 [2] 2003994-121 2007222-281
-171 217 (CSM-112, Apollo 15)
2003993-111 [2] 2003994-121 2007222-281
-181 218 (CSM-114, Apollo 17)
2003993-081 [2] 2003994-121 2007222-271
-191 219 (CSM-115)
2003994-121 2007222-181
-201 220 (CSM-115A)
2003994-121 2007222-231
-211 221 (CSM-117, Skylab 3)
2003993-111 [2] 2003994-121 2007222-281
-221 222 (CSM-118, Skylab 4)
2003993-091 [2] 2003994-121 2007222-271
LM Systems (Installation list 6014999)
-021 602
2003100-021 2003985-051 2010744-081
-031 603 (LM-1, Apollo 5)
2003100-021 2003985-051 2007222-171
-041 604 (Qualification system)
2003200-011 2003950-011
-051 605 (LM-3, Apollo 9)
2003200-011 2003950-011 2007222-221
-061 606 (LM-4, Apollo 10)
2003200-011 2003950-011 2007222-241
-071 607 (LM-6, Apollo 12)
2003200-011 2003950-011 2007222-261
608 (LM-2)
2003200-041 2003994-041 2007222-221
-091 609 (LM-5, Apollo 11)
2003993-031 2003994-091 2007222-261
-101 610 (LM-7, Apollo 13)
2003993-031 2003994-091 2007222-261
-111 611 (LM-8, Apollo 14)
2003993-071 [2] 2003994-091 2007222-261
-121 612 (LM-15)
2003993-031 2003994-091 2007222-241
-131 613 (LM-9)
2003993-091 [2] 2003994-091 2007222-301
-141 614 (LM-10, Apollo 15)
2003993-091 [2] 2003994-091 2007222-301
-151 615 (LM-11, Apollo 16)
2003993-111 [2] 2003994-091 2007222-301
-161 616 (LM-12, Apollo 17)
2003993-061 2003994-091 2007222-261
-171 617 (LM-13)
2003993-061 2003994-091 2007222-251
-181 618 (LM-14)
2003993-061 2003994-091 2007222-261
[1] The drawing isn't presently available.

[2] The latest available revision of the drawing doesn't include the configuration implied by the dash number.

[3] The part is a modification of another part, according to instructions given by a separate drawing that
isn't presently available.

[4] Addition of CDU support to this table is a work in progress, and is presently very incomplete.


The official AGC/DSKY electro-mechanical drawings available to us at the present time are these:

All of this material is hosted locally here at the Virtual AGC Project website, or else at out Internet Archive Virtual AGC site.  The best portal into this mass of available original Apollo Program engineering drawings is through our MIT/IL Apollo engineering-drawing index page.

Besides these primary sources, there are additional (sometimes overlapping) essentially complete electrical schematics available in:
These documents are theory-of-operation documents, which describe the circuits textually and often provide useful information like timing diagrams of what the circuits do.  In the process of providing this info, though, they provide the schematics themselves as figured embedded within the text.  In saying that the schematics provided in the theory-of-operation documents are "essentially complete", what I mean is that the schematics in these volumes aren't precisely in the form of the original drawings, but rather have been redrafted by AC Electronics to fit into the format of their volumes.  Thus, they are subject to mistakes (and potentially, corrections) by AC Electronics, and cannot necessarily be straightforwardly matched to specific drawing numbers or revisions.

Surprisingly, while we have schematics in one form or another for all AGC/DSKY modules, though not necessarily in all of the different forms or versions we like, and we have wiring diagrams for the DSKY backplane into which its modules are inserted, we do not have wiring diagrams for the AGC backplane.  (See this section for a discussion of how the AGC circuitry is partitioned up.)  Nevertheless, we do have enough information about it to be useful, compiled by two techniques:  Firstly, the electrical schematics for the individual circuit modules list "net names" for all of the connector pins going from the module to the backplane, so we do know how the modules were interconnected on the backplane; secondly, physical AGCs can have their backplanes mapped by means of continuity checking with an ohmmeter.  Mike Stewart has put together a helpful sqlite database and an interactive, online form of it, based on mapping out the backplane for AGC s/n 14.

Other useful resources may be available in the "AGC electrical schematics" section of our document-library page.

Besides the AGC Handbook, additional information used for cross-referencing the various drawings to specific AGC or DSKY part numbers and/or serial numbers came from a couple of sources:

Versioning the AGC and DSKY

The AGC and DSKY part-numbering scheme looked like this:

For example, Block II AGCs had PARTNUMBERs 2003100, 2003200, and 2003993, with DASHNUMBERs like -011, -021, -031, and so on.  REVISIONs were letter codes, such as A, B, C, etc., or else a dash (-) for "no revision".  For example,


Given a part number for a particular AGC (or DSKY) model, the part number then relates to a set of sub-assemblies (often represented by electrical schematics or mechanical drawings), many of which are circuit modules, which themselves may have varying versions over time, and have part-numbers like


For example, the AGC with p/n 2003200-011A contained, among other things, an "oscillator module" which fit into a backplane socket labeled B7, and which itself had a p/n 2005003E ... and naturally, we have drawing 2005003E if you want to see it.

In general, those DASHNUMBERs cover different configurations handled within the same engineering drawing.  For example, drawing 2003100 might cover both configurations -011 and -021, and you'd have to read the drawing itself to understand how unit 2003100-021 differs from unit 2003100-011.

With rare exceptions, different REVISIONs of a drawing do not introduce any design changes within a specific configuration, but may be used to cumulatively add a new configuration.  In other words, as long as a particular revision of a drawing contains the configuration you're interested in, it doesn't really matter (usually) that later revisions of a drawing may also exist, because later revisions won't differ substantively as far as any given configuration is concerned.

CAD Files

In addition to providing scans of original electrical and mechanical drawings from the Apollo program, there is an ongoing effort to transcribe these drawings into CAD files.

Such CAD transcriptions are made as faithfully visually to the original as is feasible, given the capabilities of the CAD program involved, as long as there is no compromise of electrical or mechanical correctness.  But realize that transcription is a human effort, so transcribed CAD files may at first contain errors; conversely, they may from time to time correct errors present in the original drawings — naturally, though, with suitable notes indicating that the change had been made, and why.  It has also been possible occasionally to reconstruct some currently-missing drawings from the original Apollo Program.

Electrical Drawings

As far as electrical CAD files are concerned, no community effort has developed to transcribe the electrical drawings into CAD, but it now appears as though one isn't really needed since I'm sure I can do them all myself ... eventually.  You can simply treat the CAD files as resources which appeared from nowhere, but which you are free to use or modify for your own purposes.

To do so, the open-source KiCad electrical-design software is used.  It is available, for free of course, on Windows, Mac OS X, and all of the major flavors of Linux.  The electrical schematics which have been transcribed into CAD, or are in the process of being transcribed, are stored in the "schematics" branch of our GitHub repository.  Also they are typically rendered as PNG images as well, and provided separately for convenient browsing.

There's plenty of online material to help you get started with KiCad, if you're inclined to do anything more with the CAD files as such.  Here's the executive summary of what you need to know if you want to specifically work with our electrical schematics in KiCad:

Though no help in transcription is really needed, help in proof-reading and/or correcting the CAD files vs the original drawings is welcomed, and you can contact me directly at the address at the bottom of this page if you're interested.  Just proof-reading doesn't actually require using CAD or even having expert electrical knowledge.  It just involves comparing two images like the ones below and seeing how they differ from each other (click to enlarge):

Click to enlarge  Click to enlarge

Mechanical Drawings

No mechanical drawings have yet been transcribed to CAD files (insofar as they fall officially under the aegis of the Virtual AGC project), so anything I have to say about it is somewhat theoretical.  However, based on discussions with various parties interested in the topic and/or currently working on the problem for their own benefit, here is the guidance I can offer you so far.

First, there isn't likely to be any concerted effort to transcribe the AGC/DSKY mechanical drawings into 2D CAD form, although doing so would be consistent with the efforts we've made with transcription of AGC software source code and AGC/DSKY electrical drawings.  There are simply so many such mechanical drawings (over 4000 scans at this writing) ... plus, the mechanical-engineering community has really moved past 2D design anyway, if my understanding of what I've been told is correct.  If you would like to make some 2D CAD transcriptions of the mechanical drawings, though, I am happy to accept them for inclusion in the collection.  I would ask that submissions conform to the following:

But instead of 2D drawings, the main thing in which people seem to be interested is the creation of reusable 3D models of the various fabricated parts comprising the AGC and/or DSKY.  If you wish to make submissions of that type, they should conform to the following:

Digital Simulation of the AGC Electronics

Surprisingly, digital simulation of the electronics turns out not to be incredibly difficult.  Nevertheless, discussion of the topic can be rather involved, so to keep this page relatively short (really!), a separate page is devoted to discussing digital simulation.

Basic Partitioning of the AGC Electronics

The Block II or LM AGC contains two trays of electronics, the A-tray and the B-tray.

The trays contain connectors allowing A to be connected to B, or vice-versa, and to the outside world.  Each tray also contains a "backplane" into which electronics modules can be plugged.  The A-tray modules have designations like A1, A2, ..., A31, while the B-tray modules have designations like B1, B2, ..., B17.

Each of these modules has an associated drawing.  For example, in the 2003200-011 AGC, module A1 (the "scaler" module) has electrical drawing 2005259A.  In other words, each module is considered to comprise a single circuit, with a unique (though possibly multi-sheet) drawing.

Modules A1 - A24 consist entirely of "logic": i.e., their electrical drawings consist entirely of NOR-gates and the connectors for plugging the modules into the backplane.    For this reason, I suppose, the drawings aren't called "schematics", but are often given the special name "LOGIC FLOW DIAGRAMS".  But they're schematics anyway.  Modules A25 - A31 and B1 - B17 are entirely analog in nature and are specifically called "SCHEMATICS".

As far as the construction of the circuitry is concerned, three basic techniques were intermixed:

Module with nickel-ribbon logic

Of course, these details don't matter much in modern terms unless you're very enthusiastic about building an AGC re-creation and want to do it absolutely 100% authentically.  If you were, you would be defeated in the end by the fact that the electronic components originally used, such as the dual triple-input NOR gates, are no longer available in precisely the form they were originally used.  And while I haven't priced ferrite memory lately, I expect that it's probably not terribly cost-effective.    Though, surprisingly, you can get junked ferrite-memory systems from eBay; not from the AGC, naturally, but perhaps close enough that they could be made to work if mined for parts.

The pictures in this section, taken by Mike Stewart, are of Jimmie Loocke's model 2003100-071 AGC, s/n 14.

Supplemental Information for the Block I AGC

Some modules in an actual 1003700-011 AGC.  (Click to enlarge.)

Module Description
Related ND-1021041 Figures
A1 - A16: Logic Flow Bit
A17: Logic Flow C
A18: Logic Flow B
A19, A39: Interface
A20, A40: Interface
A21: Logic Flow S
A22: Logic Flow P
A23: Logic Flow E
A24: Logic Flow R
A25: Logic Flow Q
A26: Logic Flow J
A27: Logic Flow D
A28: Logic Flow N
A29: Logic Flow V
A30 - A31: Logic Flow H
A32: Logic Flow F
A33 - A34: Logic Flow G
A35: Logic Flow A
A36: Logic Flow T
A37: Logic Flow L
A38: Logic Flow M
A39: Interface
(See A19)
A40: Interface
(See A20)
B2 - B4: Power Switch Module
B5: Filter
B6: AGC Clock Osc
B7: Driver Service
B8: Current Switch
B9: Erasable Memory Stick
B10 - B11: Erasable Drivers
B12: Power Supply Control
B13 - B14: Erasable Sense Amplifiers
B21 - B24, B28 - B29: Rope Memory
B26 - B27: Rope Sense Amplifiers
B28 - B29: Rope Memory
(See B21 - B24)
B30: Rope Strand Select
B31: Strand Gate
B32 - B33: Rope Driver

Supplemental Information for the Block I Main and Navigation DSKY

Internal views of a 1003563-051 AGC.  (Click to enlarge.

Module Description
Related ND-1021041 Figures
D1 - D3: Decoding
D4 - D6: Decoding
D7 - D10: Relays
D11 - D14: Relays
D15: Power Supply
D16: Power Supply
D17: Keyboard
D18: Keyboard

Supplemental Information for LM/Block II AGC p/n 2003100-021

This is an interesting version of the AGC, in that the logic circuitry was constructed in a very different fashion than later dash numbers of 2003100 (and the later versions 2003200 and 2003993) were.  Those later versions used multi-layer printed circuit boards to hold the integrated circuits, whereas this version interconnected them via a nickel ribbon.  The nickel-ribbon design turned out to have too much capacitance, resulting in excessive signal delay, and the design didn't function in practice.  This is what resulted in the introduction of multi-layer printed circuit boards instead.  That's not to say, of course, that there's anything wrong with the electrical schematics for this design, since the physical construction of the circuitry is basically outside the scope of the electrical schematics.  I'm told that all existing functional 2003100 AGC units are of the multi-layer printed-circuit variety.

In addition to the nickel-ribbon interconnect, the circuitry for the various modules was actually divided into four separate "quadrants" of circuitry, which were mostly rather independent but did have some interaction with each other.  Later designs removed the concept of quadrants altogether.

Besides the reference sources mentioned earlier, AC Electronics document ND-1021043 of March 10, 1966, supposedly relates to AGC p/n 2003100-021 (according to its Tables 3-I and 7-I), and its Table 8-II lists all of the associated module drawings.  But I don't believe there are any differences between the circuitry it presents and that presented by ND-1021042.

Finally, there's the question of "signal wiring diagrams".  These are related to the nickel-ribbon interconnect described above. To understand what that is and how to read one, consult the Appendix.  It should be noted that because of the later reworking of the design to replace the nickel-ribbon interconnect with a multi-layer printed circuit board, the reference designators and pin numbering from later versions is not closely related to numbering of this version of the design.

Supplemental Information for LM/Block II AGC p/n 2003200

Module Description
Related ND-1021042 Figures
A1: Scaler Module
A2: Timer
4-119, 4-120, 4-122, 4-159
A3: S Q Register and Decoding
4-122, 4-128, 4-129, 4-131, 4-132, 4-221
A4: Stage Branch Decoding
4-130, 4-131, 4-132, 4-134, 4-135, 4-136, 4-152, 4-153
A5: Cross Point Generator I
4-132, 4-134, 4-135, 4-147, 4-156
A6: Cross Point Generator II
4-134, 4-135, 4-153, 4-200, 4-207
A7: Service Gates
4-134, 4-143, 4-144, 4-145, 4-146, 4-148, 4-149, 4-152, 4-153, 4-153B, 4-155, 4-175
A8: 4 Bit Module
4-142, 4-153A, 4-208
A9: 4 Bit Module
4-142, 4-153A, 4-175
A10: 4 Bit Module
4-142, 4-153A, 4-175
A11: 4 Bit Module
4-142, 4-175
A12: Parity and S Register
4-122, 4-136, 4-142, 4-149, 4-150, 4-154, 4-155, 4-157
A13: Alarms
4-120, 4-124, 4-159, 4-166, 4-221
A14: Memory Timing and Addressing
4-141, 4-142, 4-155, 4-166, 4-200, 4-206, 4-207, 4-208, 4-218
A15: RUPT Service
4-133, 4-141, 4-142, 4-153C, 4-155A, 4-163, 4-209
A16: In/Out I
4-172, 4-176, 4-178, 4-179
A17: In/Out II
4-155, 4-172, 4-174, 4-177, 4-178, 4-185
A18: In/Out III
4-120, 4-124, 4-172, 4-173, 4-181, 4-186, 4-190, 4-218
A19: In/Out IV
4-120, 4-124, 4-178, 4-182, 4-183, 4-184, 4-187, 4-189
A20: Counter Cell I
A21: Counter Cell II
4-133, 4-164, 4-221
A22: In/Out V
4-159, 4-180, 4-187, 4-190
A23: In/Out VI
4-120, 4-153C, 4-172, 4-175, 4-178, 4-186, 4-189, 4-190
A24: In/Out VII
4-120, 4-122, 4-124, 4-135, 4-153B, 4-159, 4-165, 4-166, 4-171, 4-175, 4-178, 4-190
B7: Oscillator
B8: Alarms

Supplemental Information for LM/Block II AGC p/n 2003993

Module Description
Related ND-1021042 Figures
A1: Scaler Module
A2: Timer
4-119, 4-120, 4-122, 4-159
A3: S Q Register and Decoding
4-122, 4-128, 4-129, 4-131, 4-132, 4-221
A4: Stage Branch Decoding
4-130, 4-131, 4-132, 4-134, 4-135, 4-136, 4-152, 4-153
A5: Cross Point Generator I
4-132, 4-134, 4-135, 4-147, 4-156
A6: Cross Point Generator II
4-134, 4-135, 4-153, 4-200, 4-207
A7: Service Gates
4-134, 4-143, 4-144, 4-145, 4-146, 4-148, 4-149, 4-152, 4-153, 4-153B, 4-155, 4-175
A8: 4 Bit Module
4-142, 4-153A, 4-208
A9: 4 Bit Module
4-142, 4-153A, 4-175
A10: 4 Bit Module
4-142, 4-153A, 4-175
A11: 4 Bit Module
4-142, 4-175
A12: Parity and S Register
4-122, 4-136, 4-142, 4-149, 4-150, 4-154, 4-155, 4-157
A13: Alarms
4-120, 4-124, 4-159, 4-166, 4-221
A14: Memory Timing and Addressing
4-141, 4-142, 4-155, 4-166, 4-200, 4-206, 4-207, 4-208, 4-218
A15: RUPT Service
4-133, 4-141, 4-142, 4-153C, 4-155A, 4-163, 4-209
A16: In/Out I
4-172, 4-176, 4-178, 4-179
A17: In/Out II
4-155, 4-172, 4-174, 4-177, 4-178, 4-185
A18: In/Out III
4-120, 4-124, 4-172, 4-173, 4-181, 4-186, 4-190, 4-218
A19: In/Out IV
4-120, 4-124, 4-178, 4-182, 4-183, 4-184, 4-187, 4-189
A20: Counter Cell I
A21: Counter Cell II
4-133, 4-164, 4-221
A22: In/Out V
4-159, 4-180, 4-187, 4-190
A23: In/Out VI
4-120, 4-153C, 4-172, 4-175, 4-178, 4-186, 4-189, 4-190
A24: In/Out VII
4-120, 4-122, 4-124, 4-135, 4-153B, 4-159, 4-165, 4-166, 4-171, 4-175, 4-178, 4-190
A25 - A26: Interface
4-191, 4-218, 4-225, 4-227
A27 - A29: Interface
A30 - A31: Power Supply
4-219B, 4-220B
B1 - B6: Rope Memory
4-210, 4-211, 4-212, 4-213, 4-214
B7: Oscillator
B8: Alarms
B9 - B10: Erasable Drivers
B11: Current Switch
B12: Erasable Memory
B13: Sense Amplifier
4-204, 4-205
B14: Sense Amplifier
4-215, 4-216
B15: Strand Select
4-210, 4-215
B16 - B17: Rope Driver
4-211, 4-212, 4-213, 4-214

Supplemental Information for Block II DSKY

Module Description
Related ND-1021042 Figures
D1 - D6: Indicator Driver
4-225, 4-226, 4-227, 4-229, 4-230, 4-231
D7: Power Supply Module
D8: Keyboard Module

Appendix: Evolution of Block II AGC Part Numbers

The way different part numbers of AGCs (or DSKYs) are related to one another is that you start with a given assembly with a certain part number (such as Block II AGC with p/n 2003100-011), then you apply an Engineering Change Proposal, or ECP for short, such as ECP 322 (described as "computer wiring changes"), with the result that you now have a different assembly p/n 2003100-021. 

The list below shows how all known Block II AGC part numbers are interrelated according to the principle just mentioned.  Many of these changes clearly are not electrical in nature, or else refer to intermediate or test versions of the AGC.  Sometimes there are multiple paths to get to the same part number, if the ECPs are applied in different orders.  For example, p/n 2003993-061 + ECP 815 = p/n 2003993-071 + ECP 719 = p/n 2003993-111.  I've only bothered to show one such path below in the few cases where that happens.

Note that there is also an ECP 483 for p/n 203993 listed in Table 8-II of document ND-1021042 (from which the information above came), but I haven't been able so far to find out what it is, nor at what dash number of 2003993 it became effective.

Electronics Component Part Numbers and their SCDs

We don't have an official document, in so far as I am aware, giving the Instrumentation Lab's part numbers for electronics components like resistors, capacitors, transistors, and so on.  Many of them are deducible from other documents, like the AGC Handbook drawings.  For example, from drawing 2005952-, we can find out that part number 1006750-32 is a 1/4W 1K resistor with a 2% tolerance, while part number 1010406-7 is an 8.2 μH 10% tolerance R.F. coil.  Mike Stewart (thanks, Mike!) has done a lot of that for us, but the task is still incomplete.

The list above may not be fully up-to-date with respect to the master list, which is actually in our GitHub repository.  If you have corrections or additions to this table, I believe you can edit the table directly in GitHub, though your changes won't go live unless we approve them.

In addition to the raw list of part numbers above, we have the Specification Control Drawings (SCDs) for most of them.  In modern terms you can think of the SCD as being like the data sheets for the components, except that instead of being written by the manufacturers, they are Instrumentation Lab drawings, and serve roughly the same purpose.  We have most of the SCDs in multiple revisions, so if you're interested in that kind of thing, you can see how the specifications evolved over time.  If you want to see them, look on our AGC engineering-drawing index page.

Appendix: Signal Wiring Diagrams for the Block II AGC 2003100 and the NOR-Gate Problem

First, an elementary introductory digression, for anyone who isn't an electronics expert but has persevered in reading to this point.

When designing electronic circuitry, it is customary to assign each electrical component in the circuit a unique "reference designator" (or "refd", pronounced REF-DEE, for short), and to refer to the components by those refd's.  The refd's can be anything, but customarily they consist of a letter to indicate the general type of component — R for resistors, C for capacitors, D (or perhaps CR) for diodes, and so on — followed by a number to indicate which specific component it is within the circuit.  For example, in the typical kind of circuit diagram shown to the right, you see resistors R1 through R7, capacitor C3, transistors Q1 through Q3, and so on.

Integrated circuits (IC's) typically have U as the alphabetical prefix, thus you might have integrated circuits U1, U2, U3, etc.

One thing that happens sometimes is that a given component might actually be a conveniently packaged-together collection of several essentially interchangeable simpler parts.  For example, a "dual NOR gate" integrated circuit would be a device that provides two separate NOR gates, which are independent of each other but are packaged together to save space or cost or for some other reason of convenience.  When that happens, the overall integrated circuit still has a U-based refd, perhaps U3, but the two NOR-gates comprising it each have refd's of their own, which would normally be U3A and U3B.

The example of a NOR-gate wasn't chosen arbitrarily. In fact, since integrated circuits were a pretty new development during the early Apollo Program, and were still suspiciously unreliable and quite expensive, the AGC circuitry originally didn't use any of them.  Eventually, though, the relentless pressure to miniaturize forced integrated circuits into the design.  As it happens, the AGC ended up using a single type of integrated circuit (the DSKY used none at all), though it used lots of them.  As you've probably guessed, that one type of IC was in fact a dual triple-input NOR gate.

(Actually, that's a bit of an over-simplification, though it's largely true for our purposes.  In fact, the Block II AGC used dual NOR gate integrated circuits, as stated, but the Block I AGC used integrated circuits containing a single NOR-gate each.  Besides that, the sense amplifier modules used comparatively small numbers of sense-amplifier integrated circuits, whose internal composition is depicted in the figure to the right.  The sense amplifier integrated circuit was exactly as complex as a dual triple-input NOR gate integrated IC, in that each of them contained 6 NPN transistors and 8 resistors ... which is just an interesting factoid and is neither here nor there.  For the purposes of our present discussion, neither the Block I NOR gates nor the sense-amplifier ICs are of any relevance whatever.)

I won't bore you by telling you about the general properties of NOR gates, but to understand the discussion in this section you do need to know a couple of different things about them.  Firstly, in the AGC schematics a NOR gate is symbolized either as

and secondly, all of the three inputs of a NOR gate are interchangeable, in the sense that if you swapped any two of them, the behavior of the device would remain the same. (I suppose it may also be worth noting that of the two NOR-gate representations above, you can have two of the left-hand kind as the A and B parts of a dual NOR gate, or two of the right-hand kind, but not one of each.)

What this is all leading up to is that some of the early AGC (p/n 2003100 only) electrical schematic drawings:
  1. Do not list any ref's for NOR-gates, so we have no way of knowing from the schematics which individual NOR gate is packaged with any other into a dual-NOR IC; and
  2. Do not list any pin numbers for the NOR-gate inputs, so we have know way of knowing which of the interchangeable inputs any given input signal is hooked up to.

To get a sense of this, to the right there are two versions of a sample (nonsense) circuit consisting of NOR gates, one with refd's and pin numbers, and one without.  In the right-hand version, we know, for example, that pin U1A-J is connected to pins U1B-F, U2A-F, and U2B-F.  In the left-hand version we know that the output from one NOR gate is connected to some input or other on each of the other NOR gates.  Imagine trying to repair or discuss the left-hand version!

As far as the operation of the circuit is concerned, of course, it makes no difference at all whether or not those refd's or pin numbers are there, because all of the NOR gates are interchangeable and all of the inputs to them are interchangeable, so the OUTPUT we get from any given INPUT is still exactly the same.

In the same way, you personally may not care one way or the other which specific NOR gate is used for any given purpose in the AGC circuitry, nor may you care which input pin is which on those NOR gates.  If that's so, you don't need to read any further ... just go back to looking at the schematics presented above on this page and enjoy!

But the truth is that the original AGC developers did care which NOR gate was which and what pin number was what ... it's just that for some reason they didn't find it convenient to put that information directly into some of the schematic diagrams for AGC p/n 2003100, and hence they chose to provide it through some other mechanism.  That mechanism is the so-called "signal wiring diagram", and each of the schematic drawings in the AGC 2003100 containing NOR gates had an associated signal wiring diagram.  Below, there's a "typical" (actually, slightly more legible than usual) portion of a signal wiring diagram:

You may be forgiven for thinking that this makes the situation even more confusing to deal with, particularly since you are quite correct about it, but it helps if you know how to read it!  When you know how to read it, it tells you which NOR-gates are paired into which in the dual NOR-gate IC's, which of the pair is the "A" member of the duet and which is the "B" member, and which pin numbers the signals are hooked up to.

It doesn't tell you exactly how to specify the refd's of the dual-NOR IC's, but we know from other versions of the AGC roughly how they did that, so we'll talk about that later.

The first thing to notice is that one side of the diagram is marked as LEFT and the other as RIGHT.  In this drawing, LEFT is at the bottom and RIGHT is at the top, but in other drawings that's reversed, so try to think only of LEFT and RIGHT instead of bottom and top.

Next, notice the little numbers written along the LEFT or bottom edge (39155, 39145, 39149, ...) and RIGHT or top edge (39156, 19151, 39152, ...).  Those numbers are actually written on the NOR gates in the schematics, in lieu of refd's, and each individual NOR gate is identified uniquely by these numbers.  These are called "gate numbers".  So, a pair of such gate numbers could uniquely specify a dual-NOR gate.  The RIGHT numbers are the "A" NOR gates, and the numbers opposite them on the LEFT are the associated "B" NOR gates within the same dual NOR IC. 

Before talking about the other stuff written on the diagram, let's talk a little more about the dual-NOR ICs.  The AGC's were 10-pin rectangular packages, with the pins on them variously labeled either numerically or alphabetically, depending on the purpose of the discussion.  We might draw it like so, with the "A" NOR gate on the left and the "B" NOR gate on the right:

Ignore the fact that the NOR gates now look like little rocket ships; that may or may not be significant.  Rather, the important things to note are that there are VCC and GND inputs to power the device, that the "A" gate has pins 1-4 (or J, A, B, C), and that the "B" gate has pins 6-9 (or D, E, F, K).

If you look along the bottom (LEFT) edge of the signal wiring diagram, you'll see a repeating pattern (from left to right) consisting of

  1. a small square
  2. an even smaller circle
  3. 3 empty spots
  4. an oval with a number inside
What those represent in terms of the dual-NOR IC are:
  1. pin 10 of the dual-NOR
  2. pin 9
  3. pins 8, 7, and 6
  4. a spot unrelated to the NOR
Similarly, along the top (RIGHT) edge of the signal wiring diagram, you'll see a similar but slightly less regular pattern of 6 positions:
  1. small circle
  2. 3 empty spots
  3. 2 spots with several possible markings
And in terms of the dual-NORs, these are:
  1. pin 1 of the dual-NOR
  2. pins 2, 3, and 4
  3. 2 other things not related to the NOR.
We'll get to what those non-NOR things are later, but the point to understand right now is that 9 of each dual-NOR's 10 pins appear in a regular manner along these edges.  (The 10th pin is always grounded, and we won't worry ourselves about it.)

What about those weird, snake-like horizontal lines running lengthwise along the middle of the signal wiring diagram?  Wires!  Where the wire points downward, there's a connection along the bottom edge of the diagram, whereas when it points upward there's a connection along the top edge of the diagram.  In the image below, I've added some false coloring to just one of those snakelike lines to focus the attention on it:

So according to the description I just gave, the wire makes a connection to the following:

Now, if you know anything about electronics, you may be worried that the outputs of two different NOR gates are tied together.  Don't worry, though, these NOR-gates have open-collector outputs (or more precisely, open-collector with a pullup resistor to VCC), and so they can be tied together to increase their drive capacity (or to effectively increase the number of NOR inputs for a single output) without any problem.

Perhaps I should finally say what some of these non-NOR markings along the edges are:

At any rate, the point is that this red wire represents two NOR-gates tied together to drive connector pin 111.  Now, I didn't mention it before, but this signal wiring diagram happens to be from sheet 1 of drawing 2005061D, and if we look at that drawing, we will indeed find that connector pin 111 is being driven by NOR gates 39107 and 39155.

What is this "inter-quadrant" thing of which I spoke, and for that matter, what is a "quadrant" anyway?

For these AGC modules, the connector from the module to the AGC backplane has 4 rows of 69 pins each (numbered 1 to 71, but with 21 and 51 missing).  Each one of those rows of pins essentially has its own circuit associated with it, and these separate circuits are called "quadrants".  The concept of the "quadrant" was used only for early dash numbers of the 2003100 AGC (such as the one we have schematics for!), and disappeared for later 2003100 versions, and for the 2003200 and 2003993 AGC's, though much of the numbering of components on the schematics remains tied to the quadrant concept even if the quadrants themselves disappeared.

By "separate circuits", I mean logically separate rather than physically separated onto different circuit boards, though apparently that was originally what was tried.  And usually, the circuitry on the quadrants isn't entirely logically independent of the circuitry on the other quadrants, and in that case there have to be one or more electrical connections between the quadrants of the module ... i.e., inter-quadrant connections.

In fact, the signal wiring diagram I've been showing you isn't the complete diagram for drawing 2005061D, but simply the signal wiring diagram for quadrant 1 of 2005061D.  There are three other quadrants, and therefore 3 other signal wiring diagrams for this module as well.  Most modules have a complete complement of 4 quadrants, and thus have 4 signal wiring diagrams associated with them.  But some modules have less quadrants and therefore less signal wiring diagrams.

So now all of the questions are answered except for refd's.  For that, I want to direct your attention just above the row of gate numbers at the bottom edge of the signal wiring diagram shown above, or just below the row of gate numbers along the top edge.  You'll see a row of tiny, tiny numbers going from 1 (at the left) to 180 (at the right) there.  Or more accurately, you'll see rows of tiny smudges that may or may not be numbers, but you can still see that there are 180 of them.  Let's call these things "smudge numbers", for lack of a better term.  The IC's are numbered sequentially, starting at the end with the larger smudge numbers, where we find U01, and moving toward the end with the smaller smudge numbers, where we find U30.

Actually, there's some subtlety involve here.  For example, what happens if there's an open space, as there is in our pictured signal wiring diagram at U23?  Should we just skip U23 in our numbering altogether, or should the next position become U23 rather than U24?  You could argue it either way, but I'd vote for skipping U23 altogether, because it helps preserve IC numbering across different hardware versions.  In other words, if a dual-NOR is removed or added, it won't necessarily cause all of the refd's for the other dual-NORs to change.  But truthfully, we don't actually know what the original designers did in this regard.

Another subtlety in the IC numbering is the quadrants:  The entire circuit module consists of 4 quadrants, and if we followed the scheme just described, there would be 4 IC's labeled U01, 4 labeled U02, and so on.  Not good!  So in our CAD work we actually prefix the quadrant numbers to the IC numbering.  In other words, in quadrant 1, the IC's run from U101 up to U130; in quadrant 2, the IC's run from U201 up to U230; etc.  Thus every IC ends up with a unique number within the module, and we can still use that number to precisely identify where it is located physically.

And finally, one last subtlety:  Some of the quadrants have signal wiring diagrams as shown, with LEFT on the bottom, RIGHT on the top, and smudge numbers increasing from left to right.  Other quadrants are reversed, with RIGHT on the bottom, LEFT on the top, and smudge numbers increasing from right to left.  My descriptions above are all still correct, as long as you keep thinking of LEFT and RIGHT and ordering of smudge numbers as I've urged, rather than thinking of the top, bottom, right, and left edges of the signal wiring diagram as you might otherwise be inclined to do.  The reason for this reversal seems to have to do with some of the quadrants being on the front side, and some being on the back side, with the numbering consequently mirror imaged.

Appendix: Signal Wiring Diagrams and the Block I AGC

For the Block I AGC, problems similar to those described in the preceding section exist, though the problems and solutions are different in detail.  In fact, read the preceding section before reading this one so that you can have some background for the discussion in this section!

One problem that can thankfully be ignored in the Block I AGC is that the NOR-gate integrated circuit contains a single triple-input NOR gate, packaged in a TO-47 can, rather than two independent NOR gates packaged together in a flatpack, as in the Block II AGC.  That simplifies a lot.  You can see both a photo of such a gate (to the left) and a diagram elucidating its pinout and internal circuit (to the right).

A problem the Block I "logic flow diagrams" (schematics containing NOR gates) have that the Block II doesn't have, is that there were apparently multiple hardware generations of the Block I AGC that were mechanically quite different.  In particular, both the backplane-connector pin numbers and the means for identifying the NOR-gate components differed from one hardware generation to the next.  The schematic diagrams, meanwhile, showed the connector pin numbers and gate identification for multiple hardware generations, thus making them a tad more confusing than they might have been otherwise.

We don't actually know much about these different hardware generations, but here's our current thinking on the subject.  We think there were three separate Block I AGC hardware generations, which may have differed as follows:

For example, in the tiny excerpt from one of the Block I electrical schematics to the left, consider the NOR gate with the markings "2G5" and "65129".  "2G5" was how the gate was identified in generation "AGC 4", while "65129" was how it was identified in generation "AGC 5", according to the notes (not shown) written in the schematic itself. 

Similarly, consider the connector pin for the backplane signal "MPO".  It is marked both as pin #94 and as pin #104. The former is for AGC 4, while the latter is for AGC 5.

However, the Block I AGC schematics have the same characteristics as the early Block II schematics, in the sense that they do not display pin numbers for the (interchangeable) inputs of the NOR gates, nor do they indicate what we would think of as reference designators for the NOR gates.  Of course, since there's was a single NOR gate per integrated circuit, the gate-number markings (like "2G5" or "65129) could basically serve double-duty as reference designators, and having a separate reference designator doesn't really serve much purpose, so perhaps there weren't any at all.  Plus, each of the NOR gates in the example to the left has a single input ... but from the figure above, we know that pins 1, 3, and 5 of the NOR gate were all interchangeable, so which input is the one being used?  They probably are not all the "middle" pin, pin #3, since that wouldn't always have been the pin it was most convenient to physically route a wire to. 

At any rate, since the schematic doesn't have this kind of info in it, the information has to come from somewhere else.  It must instead be deduced instead from the so-called "wiring diagrams".  These Block I wiring diagrams, however, though quite similar in concept were quite different in detail from the Block II signal wiring diagrams described in the preceding section.  The image below is a wiring diagram for the Block I "scaler" module, otherwise known as AGC modules A33 and A34.  (Identical modules were plugged into slots A33 and A34.)  The wiring diagram itself is drawing 1006127A, while the corresponding electrical schematic drawing is 1006547G.  The original drawing was in black&white (at least, by the time we got it), but I've added various color notations to it for the purpose of this discussion.

(Click to enlarge)

Perhaps the first thing to note is that there are two separate circuits in this wiring diagram.  There's the "even" half, depicted on the left-hand side of this diagram, consisting of the columns labeled
and the "odd" half (the right-hand side of the diagram), with columns labeled
Of those, 2 and 3 are intended to represent the front sides of the circuits, while 4, 6, 5, and 7 (being mirror imaged) represent the back side of the circuits.

These two halves are independent of each other, in the sense that the only electrical connections between the two are via the backplane.  In other words, if you wanted to connect a signal in the left half of the circuit to one in the right half, the signal would have to go out through the module's connector, onto the AGC backplane, then back up into a different pin on the module's backplane connector.  There is a 142-pin connector (two rows of 71 pins each) to the backplane, with the the even half of the circuit using the even-numbered pins and the odd half using the odd-numbered pins, and in the diagram the connector pins are also depicted as circled numbers like

Each the two halves has 60 NOR gates, labeled in the diagram both by a "CIRCUIT NUMBER" and a "POSITION NUMBER", and are depicted in the diagram as objects like

The former are the normal NOR gates, while the latter are the so-called "expander" or "fan-in" NOR gates, represented in the electrical schematics by the following two symbols, respectively:

As you can see, each of these NOR gates has 4 signals, as it is supposed to, with the open circle being the output and the solid circles being the three inputs.  As as far as which of the filled-in black circles represent which inputs to the NOR gates, we don't actually have enough information about how the wiring diagrams are interpreted to be able to tell.  On the basis of the fact that these circular objects visually represent the bottom side of the NOR-gate TO-47 cans (see the figure at the top right of this section), my interpretation would be:

Of course, a mirror image of this arrangement, or indeed any other permutation of pins 1, 2, and 3 would logically be equally possible.

Note too that some or all of the NOR-gate pins have solid black lines going to them, and of course these represent the wires.  All of the fat, solid, black lines in the wiring diagram are wires.

The final factoid needed to interpret the diagram is to note that each of the circuit halves seems to have wires that exit to the left or to the right, and then just stop in mid-air, so to speak, without actually connecting to anything. Notice, however, that the wires exiting to the left and the right are exactly paired with each other: for each wire exiting to the left, there's one at the exact same position vertically exiting to the right.  This is intended to mean that those two dangling wires are connected together as the same signal.  I've added a couple of blue lines to the diagram to make this point graphically.

Actually, to avoid being misleading, I should admit that it's a little trickier than this sometimes.  The true is that there's not necessarily a unique match between the dangling wires exiting to the left and those to the right, so sometimes you have to work it out using the schematic as a reference.  The figure below is an excerpt from a different signal-wiring diagram that shows this ambiguity.  I can't really give you any advice on resolving such ambiguities, other than to say that if you trace through the wires, you'll (hopefully always) find that one of the possible connections makes no sense with respect to the associated schematic, and that the other one does.

Ignoring complications like that, which are fortunately in the minority, let's work out an example in detail.  Consider the NOR-gate with CIRCUIT NUMBER "--039" at POSITION NUMBER "02" at the upper left of the wiring diagram.  (You'll have to click on the wiring diagram image shown earlier to expand it, in order to understand the description below.)  In the wiring diagram, we see that:

So ... how well does this correspond to what the corresponding electrical schematic drawing, 1006547G, says is supposed to be happening?  Well, wonder no more!  Here's the relevant excerpt from the schematic, and as you can see, it is exactly as our interpretation of the wiring diagram says it ought to be:

But finally, a word of caution:  The match between electrical schematics and their associated signal wiring diagrams is not always as perfect as the explanation above implies.  Of course, the Apollo Program preceded the availability of computerized CAD systems which could have automatically generated error-free signal wiring diagrams (if they were even needed at all!) directly from the schematics.  In other words, both the schematics and the wiring diagrams had to be separately, manually drawn ... naturally, we'd expect occasional errors just on that account.  But it's somewhat worse than that.  Consider the example we've been using, namely schematic 1006547 and associated wiring diagram 1006127.  This block of circuitry has NOR-gates labeled "--000" through "--079", plus additional NOR gates in the range "--301" and above.  The schematic and wiring diagram match perfectly for the range 000-079, but completely differ for the range 301+, as if completely different circuits were being described by the schematic and the wiring diagram.  And that may indeed be what happened, since the wiring diagram was drawn in February 1963, some three months prior to the schematic in May 1963. Possibly there had been second thoughts about the partitioning of the circuitry into modules in the interim. Thus where the schematics and wiring diagrams match, we should feel confident in using the information we find in the wiring diagrams to supplement what we find in the schematics, but we need to be aware that they may not match, and that we must be prepared to work from whichever one of those two is "correct".

All very well and good!  But how do we know which, if either, is correct?  I suppose I'd generally vote for the schematic, if only because the wiring diagram is a much less satisfactory way of visualizing how the circuit works.  This is particular example of drawings 1006547 and 1006127, though, there are lots of circumstantial factors that would make us choose the schematic over the wiring diagram:
  • The schematic was drawn 3 months later than the wiring diagram, and is therefore more current.
  • We have 2 revisions of the wiring diagram vs 8 of the schematic, so gross errors seem less likely to have survived in the schematic than in the wiring diagram.
  • The documentation in AC Electronics ND-1021041 matches the schematic rather than the wiring diagram.

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