For ICs especially the digital kind, selecting those with the more common functions, even though it may require more packages, will allow substitutions when half of the suppliers are out of stock. Single sourced logic is OK If all that is needed can be obtained prior to the start of production. For linear devices there are times when only one supplier makes the part. Those times are dangerous, but on occasion unavoidable.

Thanks for your thoughtful responses, these are all things that I will take into consideration if I find myself doing design work in the future. For now, I'm stuck with the job of trying to keep systems operational without insights from the engineers who designed them. Finding a new op-amp that has the same slew rate, GBP, supply voltages, etc as an old op-amp is a pretty difficult task. So far, the best tool I've found has been Digi-Key's "view similar" button on their webpage, which tabulates the available options for easy comparison. I'm a little surprised that there isn't a software tool that does this kind of comparison for parts in general, instead of just what's available on Digi-Key. Digi-Key even lets you download the table as a .csv file.

 

Being in maintenance department is different than being an OEM.

For an OEM, the strategy begins with engineering design, multiple sourcing, supply chain management, procurement and stocking, all the things that I have already discussed.

Maintenance of old and new equipment require a different strategy. It would be a difficult and costly task to maintain backup supplies of every imaginable component. Instead you should be looking at replicating complete functional units.

For new and currently available equipment, maintain multiple spares where it is cost effective to do so.
For old and obsolete equipment, search for pre-owned units on the surplus market. At the repair level, be prepared to apply substitutions at the component/board/unit levels. Furthermore, be prepared to redesign/retrofit a unit in order to achieve the same functionality.

The bottom line is, components/parts/units/complete assembles will go obsolete. This is inevitable. One has to plan this into one's maintenance strategies.

 

Engineering is much more than mathematical magic bullets. Most of the most vexing problems are out of the realm of math, like most of your decisions on how to keep Paleozoic Era electrical systems operational. It more about having a passion for understanding how things work and interact. Trig and calculus enable us to solve problems but first we need to know what problem to solve.

I never said that engineering is limited to mathematical magic bullets, I was simply listing off counter examples to show how ridiculous that first comment was; the examples I gave were just low-hanging fruit, but there are hundreds or thousands of other "magic bullets" beyond those mathematical ones I listed. Engineering circles back around on itself as it progresses - experiments are done which lead to better technologies, the new technologies allow for better experiments that lead to better technologies, and on and on... Every new tool makes engineering a little easier, and allows for more to be accomplished with less effort.

 

Being in maintenance department is different than being an OEM.

For an OEM, the strategy begins with engineering design, multiple sourcing, supply chain management, procurement and stocking, all the things that I have already discussed.

Maintenance of old and new equipment require a different strategy. It would be a difficult and costly task to maintain backup supplies of every imaginable component. Instead you should be looking at replicating complete functional units.

For new and currently available equipment, maintain multiple spares where it is cost effective to do so.
For old and obsolete equipment, search for pre-owned units on the surplus market. At the repair level, be prepared to apply substitutions at the component/board/unit levels. Furthermore, be prepared to redesign/retrofit a unit in order to achieve the same functionality.

The bottom line is, components/parts/units/complete assembles will go obsolete. This is inevitable. One has to plan this into one's maintenance strategies.

This is all good stuff, thank you!

 

It would be helpful if the designers explained all their component choices, and made it clear which parameters were critical. That might also lead to better designs, if every component value had to be justified rather than "That Looks About Right".

 

I should add that JIT (just-in-time) inventory management system was lauded as the most cost efficient and effective system by most financial experts and MBA graduates in the last quarter of the 20th century. And so it is when the whole supply chain is functioning properly.

So where does JIT put us today when that system is obviously broken?

The answer is, whatever system you adopt, make sure that it has builtin redundancies, elasticity and resilience to weather the storm when it does hit, and it will always happen.

 

Much of that stuff that they teach us in engineering school is the foundation for engineering. At least that was the case when I was there. Being part of a team doing designs is OK, BUT one still should understand the whole thing, to avoid the "microsoft syndrome" of needing to release weekly corrections for flaws that should never have been released.
Usually understanding the whole thing , and understanding one's personal segment of it, is mandatory for correct engineering. Good guesses do often work, for some lucky folks, much of the time, except when they don't work.
With electrical and electronic designs, an adequate understanding, along with knowing what is available, is what works. But then to service a system the understanding needs to be deeper so as to see what is not working as it should.
The insights for that come from learning while doing, long after the formal education is completed. It is often called "experience", which is why the value of some folks efforts is much greater than others efforts. It is knowing beforehand, rather than being able to research the needed information..

 

Maintaining systems and assemblies after the original parts are not available IS Challenging indeed. At that point one does need to be able to understand just what it did when it was working. That is the first part of the process. Deciding on replacements then becomes a matter of knowing what properties are critical and which ones are not, and that demands understanding of a circuit and what it is doing/ intended to be doing. That is where the foundation is handy.

 

Maintaining systems and assemblies after the original parts are not available IS Challenging indeed. At that point one does need to be able to understand just what it did when it was working.

But as in my case I quoted it requires circuit boards etc required to be re-worked where manuf. suddenly drop support of a recently released product etc.
Very frustrating.