When troubleshooting older electronics, the usual culprits tend to be connections and capacitors. The "solid state" components, if they have failed, usually in the role of victim e.g. bad voltage input.
So I was surprised when I found an IC chip in the middle of an otherwise functional circuit that was not behaving according to its datasheet. (In this case a WD1691V support chip in a TRS-80 Model III floppy interface.) Apparently this is not so unheard of.
For 1970s/1980s era TTL integrated circuits, is there an inherent failure rate due simply to "age" itself? Were some chips — whether through their design or a bad manufacturing run — more prone to random and/or wear-out failures even after an uneventful burn-in?
How likely is it that a typical LSI IC would fail:
- simply due to shelf-life, i.e. time since manufacture?
- as a gradual side effect of routine usage, i.e. proportional to operating hours?
- only because of out-of-spec treatment, i.e. eventually something bad (voltage spike, cosmic ray, diet coke fumes…) comes along and hurts it