Section 2 - Drawing/Data Elements & Management - Reviewing Drawings of Electrical and Electronic Systems

2.40 Reviewing Drawings of Electrical and Electronic Systems. 

2.40.1 General.  Reference ASME Y14.100 and ASME Y14.5M-1994. Review all drawings of electrical and electronic systems for the following information:

1. Ensure that wires are properly identified by size, specifications and coding.
2. Sleeving must be properly identified. Sleeve should cover connections to ensure adequate protection where a possibility of shorting exists.
3. Check notes for correct soldering specifications.
4. Check that floating connectors are used only where necessary.
5. Check for conformal coating, where required, to provide adequate resistance to leakage.
6. Check that the drawings show the polarity of diodes and crystals.
7. The orientation of transistors and other parts must be specified with respect to a fixed reference point.
8. Check for hermetic sealing of connectors, where required.
9. Check to see that requirements for lacing, sleeving or wrapping are identified.
10. Analyze and evaluate assembly drawings, wiring diagrams, printed wiring board drawings and schematic diagrams for compatibility. Each drawing or diagram should refer to all related drawings or   diagrams. All reference designators must be consistent.
11. Analyze and evaluate the service rating on all connectors. Ensure that all connectors are compatible.
12. Analyze and evaluate all components for safety.
13. All levels of electrical or electronic assembly drawings must adequately describe the test requirements for the items they depict.

2.40.2 Wiring Diagrams and Wiring Harness Drawings.

1.  Wiring diagrams and wiring harness drawings should be used where appropriate. Reference ASME Y14.100.
2. The physical arrangement of wire routing components should be consistent with their layout in associated drawings.
3. Ensure that component terminals are identified in wiring diagrams. Drawings must conform to IPC-2221A & IPC-2222.
4. Ensure that the use of reference designators is consistent with related drawings.
5. Ensure that wiring diagrams identify all input and output signals.
6. Ensure that wiring diagrams identify the functions of all test points.
7. Ensure that the unit or subunit designator is noted on the drawing and is consistent with related documents.
8. Ensure that the drawing identifies grounds and shows their location.
9. Wiring diagrams must refer to associated assembly and schematic drawings.
10. Make sure that the drawings detail the use of wire numbers or color codes and that their use is consistent with that of related drawings and associated lists.

2.40.3 Schematic, Logic and Interconnection Diagrams.  Check the following:

1. Ensure that diagrams are prepared for each subunit.
2. Diagrams must identify inputs and outputs and show their tolerances.
3. Ensure that parts are shielded where grounded.
4. Ensure that diagrams show the directional alignment of all components, and that it is consistent with what is shown on associated documents.  This is especially important for components which are affected by polarity, such as batteries, diodes and rectifiers.
5. Ensure that all components are identified by reference designator and type number.
6. Ensure that schematic drawings show the capacity ratings of safety devices such as fuses and circuit breakers.
7. Values, ratings and tolerances must be shown for all components.
8. Ensure that schematic drawings identify the functions of test points.
9. Logic symbols must be used per IEEE STD 91 (X-Ref: ANSI Y32.14).
10. Reference designators must be used per ASME Y14.100.
11. Ensure that electronic symbols are used per ASME Y14.100.
12. Ensure that schematic drawings refer to associated drawings.
13. Ensure that terminals of relays, plugs and other connections are identified.

2.40.4 Printed Wiring Board Drawing.  Check the following:

1. Analyze and evaluate the printed wiring design for conformity to applicable specifications.
2. Printed wiring fabrications must conform to applicable specifications.
3. Ensure that drawings depict wiring boards in detail and identify all components. Drawings must conform to IPC-2221A and IPC-2222.
4. Drawings must be laid on a grid system.
5. Both sides of wiring board, including reduction dimensions, must be shown on the same wiring board dawing.  Ensure that front-to-back registration points are defined, precisely located and adequately controlled.
6. Ensure that marking information depicted on the wiring board drawing is consistent with what is shown on associated drawings.
7. Ensure that the wiring board makes reference to the corresponding schematic and assembly drawing.
8. The board and assembly number must be the same as the numbers shown on the corresponding assembly drawing.
9. The drawing must specify and depict conformal coating, when required.
10. Reference designators shown on the board drawing must be consistent with those shown on the assembly drawing and associated lists.
11. Ensure that plug keys and terminals are identified.
12. Wiring board drawings should not contain subunit numbers.
13. Ensure that wiring board drawing notes include the subunit prefix.
14. Ensure that masking is not used a guide for hole locations.
15. Make sure that the dimensions and tolerances for all holes are shown.  Reference ASME Y14.5M-1994.
16. Ensure that the master pattern drawing is laid out per ASME Y14.100.
17. Ensure that multilayer boards are depicted per IPC-2221A & IPC-2222.
18. When wiring board drawings are produced in digital form, ensure that their description and format are in accordance with ANSI/IPC D-350.
19. Separate views must be shown for double sided and multilayered boards.
20. Ensure that wiring board drawings include adequate Quality Assurance (QA) provisions for the manufacture of items they depict.
21. Ensure that the circuitry pattern agrees with the schematic drawing.
22. Ensure that fixed points on printed wiring boards are used as references to define the locations, width and dimensions of conductors.
23. Ensure that jumper wires are eliminated on production drawings.