Smoke Alarm Repair
A 40-year-old mains powered smoke alarm started occasionally triggering without smoke and the prime suspect (other than dust) was the main 4.7 μF 50V electrolytic capacitor.
The capacitor was checked with a Fluke 110 multi-meter
which reported a healthy 5.18 μF and a cleanup stopped the false alarms (dust is detected as smoke); but it would still beep occasionally on windy days when the mains voltage was perhaps more variable than usual.
Now came the interesting aspect of this repair, namely to check the main capacitor again but with a superior meter, the Peak ESR70
which now reported just 1.58 μF and an ESR (effective serial resistance) of 12.6 Ω which located the problem with the aged capacitor (a new capacitor had an ESR of just over 1 Ω).
This illustrates the problem of DC capacitor testing (the Fluke) over AC testing (the Peak), although it might be argued that one should simply replace 40-year-old electrolytic capacitors; getting hold of axial lead capacitors is still possible, so the repair looks very clean.
This article was written by Anwar (Andy) Shiekh originally from London, England; he repairs things to help make an income go further and presently teaches Physics in Colorado, U.S.A.
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Note: You can check his previous repair article on Nook Repair And Battery Replacement