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Line Protector Repaired

By on May 30, 2015
line protector repair










This week-end I was in hurry because the Line Protector of my old Hotpoint fridge got suddenly out of order.

ac line protector repair

It comes designed specifically for refrigeration equipment and with a max load of 10 Amp. Its brand is NUMEN and Cuba made.

line protector repairing

It has four stages of duty represented by means of 4 LEDs:

 line protector repair2

  • Bajo (red LED): this LED lights when the volt-in is low, under 92 volts. The fridge will not start and it is protected againt low-voltage.
  • Alto (red LED): this LED lights when the volt-in is high, above 130 volts. The fridge is protected against high voltage and will not start.
  • Espera (yellow LED): when you connect it (or when the electricity is restablished from a black-out) it waits for about 3 – 5 minutes to supply electric energy to the fridge.
  • Normal (green LED): when the volt-in is in a normal range (between 93 and 130 volts) it lights, so the fridge is protected too.

Note: remember the AC voltage in my country is 110 volts.

The Line Protector was fully-dead, in other words, when you connected it to the wall-outlet, it showed no signs of life, so the equipment was opened.

line protector repair3

My first search was in the AC-in circuit, and found a shorted transistor (BC337: NPN Epitaxial Silicon Transistor: switching and amplifier applications) and a shorted zener diode of 9 volts.

line protector repair4

In this case an exception had to be made, let me explain carefully: this BC337 works as a complementary pair with the BC327 (situated in front of it, look at the photo above), so I had no BC337 of spare and then I had to look for another complementary pair: BC546 and BC556 (NPN and PNP Epitaxial Silicon Transistors: switching and amplifier applications), of course it was done by consulting both datasheets.

line protector repair5

Both transistors and the zener diode were replaced in the PCB and the equipment was tested in the AC mains, look at the result in the photos below.

line protector repair6

This time the Line Protector was working perfectly and it was saved from the dump.












This article was prepared for you by Humberto Rodriguez, one of our ‘Master Authors’ from Cuba.

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  1. Gumby

    May 30, 2015 at 10:38 am

    Good fix ... thanks for sharing!

    • Humberto

      June 1, 2015 at 7:55 pm

      Thanks Gumby

  2. Ehsan Murad

    May 30, 2015 at 12:07 pm

    Thanks for sharing.I learnt some spanish also

    • Humberto

      June 1, 2015 at 7:58 pm

      Thanks Ehsan Murad.
      Spanish es un idioma muy rico en vocabulario.

  3. Yogesh Panchal

    May 30, 2015 at 1:46 pm

    congratulations!! Humberto.

    • Humberto

      June 1, 2015 at 8:00 pm

      Thanks Yogesh, you are always welcome.

  4. Paris Azis

    May 30, 2015 at 3:20 pm

    Hi Humberto,

    Another useful device saved!
    Thanks for sharing this experience and feeling.


    • Humberto

      June 1, 2015 at 8:48 pm

      Thanks Paris

  5. Albert

    May 30, 2015 at 3:32 pm

    Hi Humberto,
    I have never seen a Line protector from the inside. Thanks for your nice article on these devices.
    And nice that you could fix it, and saved it from the dump.
    But I have a said you compared the datasheets from BC327/337 with that of BC546/556. And since they are completely different concerning the Ic of both. P is .625W, Voltages are higher thus better but Ic of originally BC327/337 is 8 times higher!
    So that could be a problem if the current becomes about 0.8A since the BC546/556 only can handle a max of 0.1A.
    It all depends what they controll. If it's only some led's you need not worry, but when it is a relay or worse it probably needs more current than 100 mA.
    I don't have any schematic of a such a Line Protector but I guess you did check this on your pcb?

    • Chris

      May 30, 2015 at 7:38 pm

      I checked too for these two transistors and Albert alright!
      I'm afraid you should change the BC546/BC556 to something more powerful.
      I have at my service some BD transistors and I would advice if you have too put
      some of the BD's. I know it is a bit overkill but better then a firework. 🙂
      You can check on this site for equivalent transistors too, I use it day by day:

      • Albert

        May 31, 2015 at 12:04 am

        Hi Chris, I myself use some Russian downloaded universal >8,5 Gigabytes Off-line Database with all kinds of Transistors, Mosfets etc. from a link I found some 2 years ago.
        It was so big that it didn't fit on a DL-DVD so I start it up as a Virtual DVD from HDD using its .iso file in Windows. And mostly I search on-line beginning the frase 'Datasheet..'.


        • Humberto

          June 1, 2015 at 9:27 pm

          Hi Albert and Chris, first of all thanks for your replies and thanks for the website, I did not know this url.
          I do not have the schematic diagram of this device but I consulted first with another tech who fixes this kind of device and some others(he works in a huge workshop of a warranty and post-warranty service of an electronic shop of my country) and he told me I could use this pair of transistors (he told me he has used the same I used and they have no problems in this circuitry).
          By the way Albert, you have talked about russian transistors. I have some Russian transistors, do you know a website which have datasheets of this Russian devices?

          • Albert

            June 6, 2015 at 5:04 am

            Good question Humberto, since the Transistor Database file I found was on sites like and via-via I found new sites like (for elektronics/magazines etc.)
            On those sites you'll find a lot of pop-up spam which just keeps coming while downloading. I just keep closing them in the meanwhile I'm searching there. And I use a good firewall and Viruskiller of course too. I Never open those sites without protection. And I found a lot of interesting 'free' data. I don't thing the link with the 8.5GB database file on Mosfets etc. is still active or usable. But I will give you a message if I do find it again! Best look there on a daily basis because you'll find magazine, software etc. there.

            • Albert

              June 6, 2015 at 5:46 am

              Search also for Radio Components Database. It's not the same one I guess but I think it will also be very big and interesting.


              • Albert

                June 6, 2015 at 6:00 am

                PS: doesn't work apparently. Just type instead and will appear


                • Albert

                  June 8, 2015 at 1:54 am

                  Hi Humberto,

                  I just have finished downloading 8.6 GB of a new 9 part RAR file which forms the "Radio Components Database".

         , was my last download part and Everyone can easily download this from the start site:


                  The nice thing here is that its Free, very usefull Off-line after downloading, and every part can be downloaded after the last one without any Waiting time on the server !

                  I guarantee that works, because I've just tested it! Its new version
                  And probably including Russian Transistors since its programmed by an Russian Guy?

                  • Humberto

                    June 8, 2015 at 7:58 pm

                    Thanks Albert.

                    • Albert

                      June 9, 2015 at 9:10 pm

                      I Hope that you are able to complete this download Humberto.
                      I specially was looking for this download because you asked for Russian datasheets. It did cost me almost 2 days to download it before I could test it myself.
                      It has a total of 69063 Triodes and Diodes in its Database.
                      (Bipolar, IGBfet, Mosfet and Diodes)
                      WITH 37956 complete PDF DATASHEETS in 940 different Packages from 123 Manufacturers. Including probably some Russian components since its language is selectable in English or Russian.
                      I am sure you will like it when you see it!

              • Albert

                June 13, 2015 at 9:00 pm

                There already is a new and much, much bigger version!
                LordGrey from "Radio Component Database" reported me himself that new great complete version (now 14.9 GB !) can be found on :

                (You first have to Free register on to be able to download it. Translate Russian page easily with Google Chrome Browser to your choice of language to be able to understand it. And Use a torrent downloader to download the provided link).

                It may take a couple of days to complete your download depending on speed of your internet connection. But it will all be worth it!

                • Albert

                  June 16, 2015 at 1:33 am

                  Just completed the new Database Download version 3.6.0.x (14.9GB). Took me almost 3 days to complete from

                  Works like heaven ! With 179.290 (!!!) Bipolar/Mosfet/IGBT/Diodes/Zener en Thyristor Components.
                  And including a total of 94011 PDF datasheets (all Off-Line accessable)!!
                  in 855 Packages of 240 different Manufacturers !
                  (Including at least 2 Russian Manufacturers!!)
                  Very interesting for all Electronics Engineers WorldWide.
                  With big thanks to LordGray

  6. Robert Calk

    May 30, 2015 at 5:33 pm

    Good job saving the device from the trash bin, Humberto.

    • Humberto

      June 1, 2015 at 9:32 pm

      Thanks Robert, The device is being used witout any trouble. In my country there are some black-outs and the line voltage is not very steady

      • Robert Calk

        June 6, 2015 at 5:11 am

        Here in the USA, our politicians and president are doing their best to destroy our country and electrical system and closing power plants. We will be like your country if the American people don't stand up and stop them.

  7. Bülent NUR

    May 30, 2015 at 6:37 pm

    Excelente 🙂

    • Humberto

      June 1, 2015 at 9:35 pm

      Thanks Bülent NUR

  8. reza

    May 30, 2015 at 8:53 pm

    hi humberto
    thank u for sharing this article.

    • Humberto

      June 1, 2015 at 9:48 pm

      Ok reza

  9. Hem

    May 31, 2015 at 5:21 pm

    Hi Humberto,Good job where can I get the schematic thanks

  10. Mahmoud

    May 31, 2015 at 8:52 pm

    thanks for sharing ... and Nice work

    • Humberto

      June 4, 2015 at 8:33 pm

      Thanks Mahmoud. You are welcome.

  11. mahmoud_tajpour

    June 1, 2015 at 3:48 am

    hi humberto thanks for your best article but my question is why were burned TR.and zener D.

    • Humberto

      June 4, 2015 at 8:18 pm

      Hi mahmoud_tajpour, I suppose this components were burned due to any instability in the AC line, it's very frequent in my country. this kind of defect is very common in this equipment, there are a lot of them in my country because they are manufactured here in Cuba.

  12. MAYOWA

    June 1, 2015 at 7:42 pm

    This is pretty good. It's a nice job.

    • Humberto

      June 4, 2015 at 8:26 pm

      Thanks MAYOWA


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