6 ms·

I'm pretty sure what makes that stuff so expensive is all the Quality Control for every single part. Its probably quite a linear cost vector they have.

C1sc0cat 6y ago
The failure to a "repaired PCB" stands out just scrap the damaged one would make more sense.
- rckoepke 6y ago
  Being that this was 1971, it was probably more straightforward to repair the botched installation/repair rather than do the whole PCB over from scratch. Features on PCB's were much simpler then, not to mention much larger. Their procedure was to test each component before installation only, in order to prevent any potential damage occurring during post-installation testing. So they evidently couldn't know to scrap it and replace the damaged one. After the Mariner 8 failure, they changed this testing policy to test PCB's/components again after components are installed on the PCB. "A diode intended to protect the system from transient voltages was thought to have been damaged during repairs/installation of the pitch amplifier's printed circuit board, something that would not have been detected through bench tests." - Wikipedia, but I'm having difficulty finding any original sources that validate or expand upon this. P.S. I think you may have responded to the wrong parent comment Edit: "N72-13963" was a report given to Congress in October 1971 on the failure of the Mariner 8 mission, I can't find that report but it may have more details if you're curious enough to track it down. Edit: I found a transcript of the report given to Congress, evidently in June of 1971: https://books.google.com/books?id=7FQVAAAAIAAJ https://books.google.com/books?id=7FQVAAAAIAAJ Dr. Low: The diode was external to this integrated circuit, mounted next to it. I don't have one with me, but the diode is another component about the same size. The integrated circuit which failed is known to be sensitive to electrical transients if it is not properly protected. And electrical transients large enough to damage an unprotected integrated circuit — caused, for example, by engine start, stage separation, et. cetera — are well within the specifications of the Atlas/Centaur vehicle and are clearly possible. Because of this, the integrated circuit was protected with Zener diodes which in effect were designed to act as "safety valves" to prevent potentially damaging electrical transients from reaching the integrated circuit itself. In accordance with standard practice in the Atlas/ Centaur vehicle — as well as in many others — these Zener diodes were checked individually prior to their installations, but were not tested thereafter. This practice of not testing protective devices after they are installed in a system is based upon the conclusion or design philosophy, which we are now reevaluating, that a test of a protective device after installation is not warranted where such a test could possibly damage the component that is being protected. Based upon the detailed consideration of the flight failure records and some very extensive "detective work" of personnel from the Lewis Research Center, which is responsible for the Centaur stage, and General Dynamics, the prime contractor, we developed the following hypothesis which we believe pinpoints the cause of the Mariner 8 failure : (1) One of the Zener diodes which was intended to protect the inte-grated circuit in the Centaur pitch rate gyro preamplifier was either installed improperly, was faulty itself, or failed at some time during assembly, vehicle checkout or powered flight. (2) An electrical transient sufficient to cause damage to the inte-grated circuit occurred some time after T-minus-40 minutes—when the autopilot performed properly--but before Centaur main engine start. (3) This damaged the integrated circuit affecting the gain of the autopilot pitch channel and causing the subsequent fixed engine position. Tests show that all subsequent mission events would be fully explained by this hypothesis. ... To prevent a recurrence of the problem which occured on Mariner 8, we required additional thermal and vibration tests on the Centaur state autopilot and new and special test procedures to ensure that the diodes protection the integrated circuits were properly installed and operative."
  - KineticLensman 6y ago
    > Being that this was 1971, it was probably more straightforward to repair the botched installation/repair rather than do the whole PCB over from scratch As an extra data point I did a contracting gig in early '90s that involved building a diagnostic system for a specialised analogue circuit board that was used in the oil industry. The boards were held in place and an automated probe system took measurements at numerous places. A constraint satisfaction algorithm then modelled failing components in an attempt to match the faulty readings, and thus locate the failed component(s). The algorithm came from a three-year Ph.D project funded by the company concerned, and I was part of a team of five that were implementing it over a six-month period. This was considered a small price by the company, compared with the cost of throwing away a specialised board manufactured in small production runs to high tolerances. The probing system already existed, and was used by electronics experts who were attempting to perform the same diagnostic process using their own (expensive) skill and judgement.
    - rckoepke 6y ago
      Just out of terrible curiosity, was that PCB used in downhole tools?
      - KineticLensman 6y ago
        They were used in a monitoring / comms role at the well head if I recall correctly. Younger me just concentrated on coding the diagnostics, and as a contractor was totally insulated from actual users who might have explained.

C1sc0cat 6y ago

The failure to a "repaired PCB" stands out just scrap the damaged one would make more sense.

rckoepke 6y ago
Being that this was 1971, it was probably more straightforward to repair the botched installation/repair rather than do the whole PCB over from scratch. Features on PCB's were much simpler then, not to mention much larger. Their procedure was to test each component before installation only, in order to prevent any potential damage occurring during post-installation testing. So they evidently couldn't know to scrap it and replace the damaged one. After the Mariner 8 failure, they changed this testing policy to test PCB's/components again after components are installed on the PCB. "A diode intended to protect the system from transient voltages was thought to have been damaged during repairs/installation of the pitch amplifier's printed circuit board, something that would not have been detected through bench tests." - Wikipedia, but I'm having difficulty finding any original sources that validate or expand upon this. P.S. I think you may have responded to the wrong parent comment Edit: "N72-13963" was a report given to Congress in October 1971 on the failure of the Mariner 8 mission, I can't find that report but it may have more details if you're curious enough to track it down. Edit: I found a transcript of the report given to Congress, evidently in June of 1971: https://books.google.com/books?id=7FQVAAAAIAAJ https://books.google.com/books?id=7FQVAAAAIAAJ Dr. Low: The diode was external to this integrated circuit, mounted next to it. I don't have one with me, but the diode is another component about the same size. The integrated circuit which failed is known to be sensitive to electrical transients if it is not properly protected. And electrical transients large enough to damage an unprotected integrated circuit — caused, for example, by engine start, stage separation, et. cetera — are well within the specifications of the Atlas/Centaur vehicle and are clearly possible. Because of this, the integrated circuit was protected with Zener diodes which in effect were designed to act as "safety valves" to prevent potentially damaging electrical transients from reaching the integrated circuit itself. In accordance with standard practice in the Atlas/ Centaur vehicle — as well as in many others — these Zener diodes were checked individually prior to their installations, but were not tested thereafter. This practice of not testing protective devices after they are installed in a system is based upon the conclusion or design philosophy, which we are now reevaluating, that a test of a protective device after installation is not warranted where such a test could possibly damage the component that is being protected. Based upon the detailed consideration of the flight failure records and some very extensive "detective work" of personnel from the Lewis Research Center, which is responsible for the Centaur stage, and General Dynamics, the prime contractor, we developed the following hypothesis which we believe pinpoints the cause of the Mariner 8 failure : (1) One of the Zener diodes which was intended to protect the inte-grated circuit in the Centaur pitch rate gyro preamplifier was either installed improperly, was faulty itself, or failed at some time during assembly, vehicle checkout or powered flight. (2) An electrical transient sufficient to cause damage to the inte-grated circuit occurred some time after T-minus-40 minutes—when the autopilot performed properly--but before Centaur main engine start. (3) This damaged the integrated circuit affecting the gain of the autopilot pitch channel and causing the subsequent fixed engine position. Tests show that all subsequent mission events would be fully explained by this hypothesis. ... To prevent a recurrence of the problem which occured on Mariner 8, we required additional thermal and vibration tests on the Centaur state autopilot and new and special test procedures to ensure that the diodes protection the integrated circuits were properly installed and operative."
- KineticLensman 6y ago
  > Being that this was 1971, it was probably more straightforward to repair the botched installation/repair rather than do the whole PCB over from scratch As an extra data point I did a contracting gig in early '90s that involved building a diagnostic system for a specialised analogue circuit board that was used in the oil industry. The boards were held in place and an automated probe system took measurements at numerous places. A constraint satisfaction algorithm then modelled failing components in an attempt to match the faulty readings, and thus locate the failed component(s). The algorithm came from a three-year Ph.D project funded by the company concerned, and I was part of a team of five that were implementing it over a six-month period. This was considered a small price by the company, compared with the cost of throwing away a specialised board manufactured in small production runs to high tolerances. The probing system already existed, and was used by electronics experts who were attempting to perform the same diagnostic process using their own (expensive) skill and judgement.
  - rckoepke 6y ago
    Just out of terrible curiosity, was that PCB used in downhole tools?
    - KineticLensman 6y ago
      They were used in a monitoring / comms role at the well head if I recall correctly. Younger me just concentrated on coding the diagnostics, and as a contractor was totally insulated from actual users who might have explained.