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Repair of Fuyuang 55V 250VA Li-ion charger

By on March 24, 2015











A not working (of course) LI-ION charger was brought to me for an inspection. And someone probably shorted this charger because they assumably changed the in and out cables when plugging in to the 230VAC power grid. (Because the ingoing and outgoing plug “Mickey Mouse- they are called- if I’m correctly informed” of the charger looked completely identical !).

It was a 55V Li-ion Battery charger with a heavy 2.5 Ampere current and 250VA Power 100- 240V 50-60Hz circuit.

(Output 48VDC 2.5 Ampere : See photo sticker bottom box below text).

Repair of Fuyuang 55V 250VA Li-ion charger

Opening of the box was only possible after cracking open the plastic top and bottom sides with the right screwdriver. (like it is often the case). The result was the next photo showing the copper solder side of the pcb.

power adapter repair1

And the next Photo explains why I still couldn’t see the components.


Because there were 2 Aluminium bended Cooling profiles on top. I had to desolder the one with the attached Power Mosfet, to be able to see the components in charge (at least they where before it broke down! Haha).

power adapter repair2

After removing the Alu profile I could oversee all components. And it turned out that the Mosfet (of type 20N60 C3) was shorted on all pins and 1 or 2 resistor’s had gone too in the

circuit of the PWM controller (a LD 7550B IC PWM Green controller). Just as the Fuse (a 3.15 AT 250VAC bigger 32 mm type with solder wires).

The above mentioned Green PWM Controller LD 7550B is an 8 pins DIP chip. Soldered left from the middle of the pcb right under the 20N60C3 Mosfet. On the right side of the Mosfet there is the Reservoir Elco that holds a firm 320 Volts DC or more when charged. And only the Fuse, , the Mosfet and the 8 dip controller, plus 1 or 2 resistors around the controller were blown. I replaced the Mosfet and the controller and other defect parts. And before testing it live on the 230 VAC 50 Hz grid, I of course used a bulb of 60 Watts 230 VAC which I placed over the wires of the blown fuse. To prevent a big power surge from happening and blowing up everything in the fuse box at home, including the already replaced components – in case if the charger still was shorted or malfunctioning !

power adapter repair3

The above picture shows the High Voltage Elco and left under top of the Mosfet 20N60C3. And completely on the left we can still see a bit of the replaced LD 7550B controller.

The red tape on the right shows the replaced 3.15 AT fuse.

As we can see this is the 230 V input charger side. With the Graetz diodes and the filter above in the photo. The safe 55 Volt charging side is on the left side from the Transformer.

The next photo shows the 8 pins power controller IC (top view) and on the right we can see the top of the Mosfet 20N60C3. In the black shrink tube below was one of the defective resister’s I also replaced.

power adapter repair4power adapter repair5

The above picture shows the charger secondary “Safe side” with the Optocoupler (a 4 pins type chip).

power adapter repair6

And above photo shows the top view of the Transformer and the secondary side. The Mosfet lookalike below on the right was 100% okay when tested with the diode test on my meter and not part of the primary circuit side. And is surely a Dual Power Diode. And both its outer pins had a ferrite.
The picture below shows the replaced Power Mosfet 20N60C3. To be exact we must notice the ferrit on the middle pin of our Mosfet. (To prevent it from oscillating …).

power adapter repair7

After a final bulb test it proved that this charger worked again splendidly. And later I found out that this kind of chargers also exist with twice the power of this charger current. (5 Amps and 55 Volt => for 48 Volt Li-ion). And they are used for electric scooters !

This charger was for someone’s electric transporting device, but since I never saw it I’m not sure what it exactly was, or how it looked. But their charger was as new again !

Mission accomplished as the Jestine Site often states !!

power adapter repair8

On the above page I’ll finally show the top and bottom of the Charger box and its “Mickey Mouse” Cable.

power adapter repair10

And above photo demonstrates that the Supply really works !

Good luck in repairing !

Cheers !!

Albert van Bemmelen, Weert, The Netherlands.

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  1. Robert Calk

    March 24, 2015 at 10:30 pm

    Good job Albert and thanks for sharing the article with us. Do you use a DMM to check the MOSFETs? Using an Analog VOM that has X10 Ohms is much better for testing MOSFETs and most components.

    • Albert

      April 26, 2015 at 1:17 am

      Hi Robert, Probably if you want to know the RDs resistance of an active Mosfet but I really don't use any old analoge meter anymore. I have several digital Semiconductor testers for testing Mosfets and other parts. But mostly I start checking for short circuits with my Digital universal meter set to Diode test.
      My Semiconductor tester(s) can test Mosfets, Triacs, Thyristors, Diodes , Resistors and Capacity/ESR. But besides my old electronics hobby, I now am learning how to Design with VHDL to make my own circuits.


      • Robert Calk

        April 26, 2015 at 4:39 pm

        Hi Albert,

        Sorry, I meant X10K, not X10. Anyway, the VOM with X10K has the added 9V battery which makes it better for checking components than a DMM because the meter uses 12V. I also have a Peak Atlas DCA75 Pro that I use for MOSFETs, etc. Plus the VOM with X10K is good for checking MOV's, Thermistors, etc. Not having a good VOM limits people. In a lot of instances, the VOM is much more valuable than a DMM. I can't wait to find out what my new Zen50 is capable of. Keep the good articles coming!

        • Albert

          May 4, 2015 at 2:44 am

          Hi Robert,

          With VOM I understand that you refer to an analog meter. And they can be costly as I saw on E-bay ($239?). I also have a big 25 year old cheapish analog Russian meter with matching aluminium box. Also a 10MHz portable Russian Oscilloscope, a 2 x 40 MHz Kenwood scope with digital Read-out. An LCR meter, and an 250 MHz Leader Griddip meter. And about 3 years ago I bought a defect and old Philips PM3234 10 MHz Memory oscilloscope which I later repaired. (The special picoampere diodes needed to repair the scope input amplifiers were a bit expensive and in 35 years or more luckily still available).

          I also made stuff like a VGA monitor testgenerator (with a PIC) with software from a Russian guy on the internet. And I'm always looking to expand my Electronic Tools in my Electronics Shack (in little bedroom).
          And of course I use a Hot solder gun for new SMT pcb's or a solderstation (25 year old Ersa).


          • Robert Calk

            May 4, 2015 at 7:12 pm

            I also have limited space, and limited budget. Many people believe that VOM's (analog meters) are obsolete and are selling them pretty cheap on Ebay, etc.
            I bought a great discontinued BK Precision 114A VOM with X10K for less than $30US, shipping included. It was still new in the box and never used!
            I've learned that we have to be more specific when using the search engine on Ebay. I had to search the names of meters because just searching "VOM or analog meters" didn't help me find the good deal. When I typed in " BK Precision meters" is when I found mine. The seller was in Texas also where I live.
            I did get burned a couple of times on some fake meters that claimed to be Sunwa's. But I did get my money back.
            Sometimes it's a pain in the neck, but if you don't give up there are some really good deals waiting! Just be more specific in the search engine.
            You will see my new BK Precision 114A VOM featured soon in an article. I'm waiting on some Diacs and caps to get here so I can finish the article.
            Hopefully my article "Playing with IC's Part 2" will be finished in a couple of days. I ordered 10 of the FR9882 IC's from Aliexpress and they were shipped to me from China with no ESD protection at all! So I'm not sure if any of them are any good. The first one blew in about 5 seconds before I could take a photo, but was outputting 3.4V on the same circuit setup as used in the first article except that now I have the 26.1K 1% resistors that the schematic calls for. I bought some tiny breakout boards to help make it easier on my back. I hope at one of the IC's are good!

            • Albert

              May 5, 2015 at 3:58 pm

              Hi Robert,

              I am also waiting on parts from China for a new Power Supply repair (400Watt ATX) I am trying to fix. I must read your "Playing with IC's part1" article again to understand what you are writing in about part2 in the making. I'm also low budgetted and am very glad that there is PayPal and E-bay to get new or old electronic parts. Hope to see your new article soon !
              By-the-way: Since you are very fond of using your Analog meter, I checked on my Russian u4341 analog meter. It was unused for very long in it's protective aluminium box but when I opened the case I noticed that the protective rubber/synthetic in the box cover started deteriorating and had badly infuenced the frontpanel plate a bit. This meter's DC Rin = 16.7kOhm/V, and its AC Rin = 3.33kOhm/V. This meter also measures hfe of npn/pnp transistors, Resistors, Current and Voltage. Good thing I looked at it to prevent it from further damage.
              (Something that also happens to modern rubberized products like mouses that get very sticky after some time etc.)


              • Robert Calk

                May 6, 2015 at 7:43 am

                I have heard people talking about the Russian analog meters. It seems like most people like them.
                Yes, we have to take care of our tools and meters. I try to check the batteries in all my meters every month.
                I wish I could afford to start collecting old meters.

  2. randy warren

    March 24, 2015 at 10:35 pm

    heck of a job, how long did it take, and do you actually earn money repairing something with a fairly cheap replacement cost (I assume?)

    • Albert

      April 26, 2015 at 1:08 am

      Hello Randy,

      If I had enough money I wouldn't have to repair and could buy everything that got broken.
      But serious, No I do this for at least 30 years as a nice hobby. In my hometown there's no job in electronics ! (I had the stupidest jobs with the matching salary in the past). The repair din't took long at all (about a half hour I guess, it costs longer for the parts to arrive from China! At least 3 weeks !!). I have very good test equipment at home.


      • Robert Calk

        May 4, 2015 at 7:32 pm

        That's because Electronics repair shops don't advertise, at least here in the US they don't!! If they would get together and advertise showing people how much money they could save, they would get much more business. They would also need more help which would mean jobs for people. I'm disabled and just repair stuff as a hobby and to have something to tinker with, but advertising would create jobs for younger people.
        I just don't understand it. Not advertising their business is like putting a noose around their own neck IMHO.

  3. Yogesh Panchal

    March 24, 2015 at 11:57 pm

    thanks for sharing your experience.

  4. Vasile Petrica

    March 25, 2015 at 2:02 am

    Good presentation,thank you.

  5. Anthony

    March 25, 2015 at 2:23 am

    Great job Albert with very nice photos, Thanks for sharing !

  6. Mark

    March 25, 2015 at 5:58 am

    Hey Albert,

    Thanks for the detailed repair. You seem to have a good understanding of IC operation and testing. I have always struggled with that. Can you recommend any books or sites that provide tutorials on IC testing?

    Once again, congratulations on an excellent article and photos.

    • Albert

      April 26, 2015 at 1:25 am

      Good question Mark but I do not know what I could recommend you. I do not know what you already know and what equipment you use at home at this moment.

      Also because I learned most stuff about 35 years ago. I guess that the most important thing to keep in mind is, that you start working safe when testing Power supplies !! Since 240 VAC or less can be deadly !

      With good equipment and a good working table you are half way !


    • Robert Calk

      April 26, 2015 at 8:45 pm

      The third edition of The Art of Electronics just came out a few months ago. I bought one and it's an excellent book - not much on testing though. On testing them, If the voltages on the inputs and outputs are good, the IC should be good. Of course you would have to make sure that some surrounding components were not causing the I/O's to be wrong.
      But as far as understanding the operation of IC's and electronic components, I don't think that there is a better book than the new, The Art of Electronics, Third Edition.

  7. Abdul

    March 25, 2015 at 10:46 am

    Thank you for sharing this article and your experience.
    Hope to hear more from you.
    Abdul (Singapore)

  8. Mohammed Kasim

    March 25, 2015 at 12:10 pm

    Congratulations for an excellent article and photos. Infact I deal with these types of chargers for Lead acid cell.

    • Albert

      April 26, 2015 at 1:37 am

      Li-Ion cells can explode when the voltage is incorrect ! 200 times deep decharching the cell, and recharging it is the average lifetime of a Li-Ion cell as I've read somewhere.

      A lead Acid battery cell is 2.3Volt charged and 2V each cell is an empty battery cell. And a few times (only 2 times?) deep loading it below this voltage can destroy the Lead Acid battery at once and the Lead Plates deform beyond repair.

      That's all I know about them. It's still an advancing technology.

      Glad that you liked the article Mohammed!

  9. Humberto

    March 25, 2015 at 9:31 pm

    Good job, congratulations.

  10. Albert Hoekman

    March 26, 2015 at 11:15 pm

    Good job namesake!
    I also did repair some chargers, they are used for charging bicycle batteries.

    Goed werk naamgenoot!
    Ik heb er ook al enkele gerepareerd, deze worden gebruikt voor het laden van fiets accu's

    Albert Hoekman, Tiel

  11. Lloyd Bond

    March 27, 2015 at 1:39 am


  12. reza

    March 28, 2015 at 5:20 pm

    thank u.


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