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UPS-SL650 repaired

By on December 3, 2015
ups transistor repair









This UPS (Uninterruptible Power Supply) was brought to me with the purpose to replace the seal lead acid battery rated as 12v/7Ah.


When the device was disarmed look what I saw:

UPS-SL650 repaired

As you can see there were three bulged e-caps and a lot of dry solder joints and the PCB was black in some places indicates heating problem in the components.

The three e-caps (2 x 1000µF/35v and 1 x 220 µ F/35v) were replaced.

bulgy cap

The dry solder joints were reestablish with fresh tin and the new battery was replaced.

ups battery

When the device was connected into the AC-mains and switched on, it was switching continuously from Normal operation to Back Up operation (inverted mode) once and again.

ups inverted mode

At this time the job continued, my first doubt were the relays, therefore they were extracted from the circuit.

ups circuit


They were checked with a DC Power Supply and a Digital Multimeter, and all of them were ok. The components situated around the five relays were checked one by one with the DMM, and know what? A crystal diode was de-soldered from the circuit, I realized from this situation by chance because I was touching some components with the tips of the DMM

transistor in ups

The relays were re-connected again. This time the UPS was tested with the connection of the AC-mains and look at the result  .

ups repair













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

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Note: You may check his previous repair article in the below link:




  1. Parasuraman S

    December 3, 2015 at 10:49 am

    Good Job! Looks like it was brought to you after tampering!

    • Humberto

      December 4, 2015 at 11:39 pm

      Yes Parasuraman, another tech reviwed it before me.

  2. Yogesh Panchal

    December 3, 2015 at 2:20 pm

    Good job Humberto and thanks for sharing.

    • Humberto

      December 4, 2015 at 11:31 pm

      Thanks Yogesh

  3. Robert Calk

    December 4, 2015 at 6:23 am

    Good job getting it fixed, Humberto. The new e-caps look like cheap ones and may not last very long.

    • Humberto

      December 4, 2015 at 11:41 pm

      Yes Robert the new ones are not high quality; remember the restrcitions of my country.

      • Robert Calk

        December 9, 2015 at 2:10 am

        Yeah, I forgot about that. My apologies, Humberto.

  4. Chris

    December 4, 2015 at 8:45 pm

    Nice job done, congratulation!
    I have questions about you repair result:
    1. Is the man AC voltage in your country 110v/60Hz?
    2. I hope the UPS did not work on an output voltage of 98V or under?

    I had some trouble with testing relay's before, some time they worked when I tested them but actually they was bad. So I decide to make a small tester for relay's with a micro controller and a PC software.
    I connect the relay to the uC and let them toggling on some frequency's
    and I count how many times was the relay powered on and how many times where the working contact shorted and that is sent to my PC.
    I test relays for 2-5 min's.
    The result should be like this: one power on should indicate one closing contact ( or releasing ). If there is some difference between the power the coil of the relay and the closing of the working contact then the relay failed.
    There is simpler ways too to achieve this result but this was for me an easy task and I love to work with uC...

    However, god job done.
    My best regards.

  5. Humberto

    December 4, 2015 at 11:47 pm

    Hi Chris 110v/60Hz in my country, the 98v is due to a new Baterry, remember it had to be charged first, that's why the 98V. When it was just repaired I performed that measuring with my DMM.
    Thanks anyway.

  6. Ulises Aguilar Pazzani

    December 5, 2015 at 1:07 am

    nice job Sir

  7. Albert van Bemmelen

    December 5, 2015 at 5:23 pm

    Hi Humberto. nice repair. Thanks! I also liked the post Chris wrote about testing relays. It could be a very handy tool as DIY relay tester project! Indeed Relay contacts tend to get bad after many high current switching moments. The only way to normally be able to see this, is to open them. With the solution of Chris you don´t have to.

    • Owais Akhter

      May 14, 2017 at 4:07 am

      Hi All,
      Galco Repairs,Global Electronics Service and many well known repair companies experts directly changed Relay, Opto-Isolator even they found good after load test. The reason for that is these components work very frequently and in high speed switching in UPS or other Types of Inverters.That is why their repairing is not just repair but refurbished equipment.

  8. Albert Hoekman, Holland

    December 8, 2015 at 8:23 pm

    Good Job Humberto. Thanks for sharing this nice article.

  9. ron

    December 12, 2015 at 8:39 am

    Thanks for your info.

    Ur pretty smart guy!!

    Thanks again.


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