Are you Walters, back again? Same kind of name as the other names you used here and on other forums (Billymayo, Dannydavis, Prescottdan, Davewalker, Castillovan and Vancastillo).
Electronic circuits are so reliable that they rarely fail today if they are designed properly and conservatively. If a consumer product fails then the product is thrown away and replaced, not repaired.
I think those old circuits for old airplanes should be thrown away and replaced. Maybe you should also be replaced.