Well, those very contacts had oxidised enough (because they probably weren't dusty) that they weren't supplying voltage. The flowing current was burning through/piercing the oxidised layer on the contacts. And these contacts, through which the current flowed close to zero - stopped contacting.
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I've probably had about a dozen cases like this too. If the relay switched a very small current it stops conducting after a few years. If you apply a higher load and switch the contact on a ball of times, it somehow clears the contacts and the relay continues to work.
>>21549550 .
I know, it was just so verbally cool to put together.
And the best contacts in relays tend to be platinum. I had one that ran for years under highly exaggerated currents and cleaned every 2 years it lasted forever.
I also remember platinum being stolen in lifts.
If there is a known problem that some relay is malfunctioning then by slightly hitting it with a screwdriver it may revealed when is in conducting state.Also if the relays of the circuit are commercially available in a reasonable cost then is a good option to replace them all at once.Especially in car pcb's if the problem is common then probably there are available spare parts,as relays for the doors locks for example.This goes to relative small and low cost relays found in commercial pcb's and easy available.
The discussion focuses on methods to check electromagnetic relays, emphasizing the limitations of using an ohmmeter alone due to its low test current, which may not reveal contact faults such as corrosion, mechanical damage, or oxidation that manifest under load. Measuring contact resistance with an ohmmeter can indicate continuity but often fails to detect issues that appear only at higher currents. Testing relays under load using incandescent bulbs or specialized testers (e.g., Testboy) provides a more reliable diagnosis by simulating real operating conditions and revealing contact degradation through voltage drop or flickering. Visual inspection of contacts, especially in relays with transparent housings, is also important. The coil resistance should be measured first to confirm coil integrity. Some relays have gold or platinum-plated contacts to reduce oxidation and improve longevity. Thermal imaging is recommended for contactors and high-current relays to detect overheating contacts. The discussion also notes that relay failures can be intermittent and that testing in the actual circuit with appropriate load current is often the most effective method. The importance of understanding relay specifications, such as minimum or self-cleaning current, is highlighted for proper testing and maintenance. Summary generated by the language model.
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