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Servicing Relay

By on September 14, 2010

relay switch

Have you service a relay before? I’m not referring to the solid state relay but the common electromechanical relay that is found in Monitor/Tv board. Electromechanical relays have a moving plate with contacts on it, while solid-state relays work similar to transistors and have no moving parts. The contacts in the electromechanical relay are pulled towards the electromagnet while current is flowing it. The contacts are connected to a spring that pulls them back when the current stops flowing. If this contact have problem , it will cause intermittent problem. You can sometimes gently knock on the relay with the handle of the screw driver to see if it has problem or not. Do not knock it too hard otherwise you may think that the relay have problem. In other word, a good working relay may show problem if you hit it too hard.

Assuming the relay have problem, you can use a small saw to saw or peel off the cover. Then you can use a sand paper on the contact point. Sometimes you could see black burnt mark on the contact point. Seal  the cover back with super glue once you have done the servicing.



  1. karlo

    September 14, 2010 at 10:12 am

    Have done similar approach since the relay is obsolete. I used a sandpaper to clean the contacts and it works fine again. But in some cases, I use a substitute. If the relay footprint is not compatible with the original, I usually mount it in a perforated PCB and use wires to complete the connection.

  2. admin

    September 14, 2010 at 10:48 am

    Hi Karlo,

    Thanks for the great info!


  3. Waleed

    September 14, 2010 at 3:28 pm

    I always use new relays because they are too cheap in my country. repairing the relay takes time and sometimes time I do not have. One case situation I do the relay repair, if I do not have a new relay to replace.

  4. admin

    September 14, 2010 at 7:31 pm

    HI Waleed,

    Yes you are right, relay is cheap but sometimes it is not easy to find from the market because the pins and the spec were different.


  5. Reynolds

    September 14, 2010 at 8:09 pm

    There was one time I am fixing an APC UPS the culprit is it will work on battery but if the regular electric is back the ups will not work it will turn off after checking all the circuit found out that the relay is defective I have try to clean it but one of the contacts is totally burn what I did I buy a new relay and just soldered some wire on it to connect it back to the PCB. By the way before I dont have any idea on how to check relay but after I bought the PDF book of sir justine the Testing Electronics Components it really helps a lot and learn so many more tricks that I have not learned in my school days. thanks to great mentor Sir Justine

  6. admin

    September 15, 2010 at 7:06 am

    HI Reynolds,

    Thanks for the sharing!



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