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Found 4 Faulty Components In A Battery Charger

By on February 26, 2022
battery charger repair

A guy who owns an electrical supplies shop brought this charger to my shop for repair. He explained that this charger was worked on before but for some reason was not able to bring it back to life.

bosch battery charger repair

It is a Bosch battery charger and that is a good quality one so I did not hesitate to look into it; I took it as a challenge since the other technician was not able to repair it. Let the fun begin.

Four screws on the bottom and the cover was lifted up and I was able to expose the disaster waiting for me inside, take a look

how to fix a broken a bosch battery charger

That is what I saw the moment the cover was lifted up and there is more.

bosch battery charger fix

For some reason, the diodes were cut while they were on board. That is strange.

pcb repair battery charger

This Mosfet was already de soldered off and was kept on board and my first thought; since all these components were found inside this charger, why the technician did not replace them to see if it works or not? I shared this thought with the shop owner and he explained; the technician did replace the parts but for some reason it was shorted again once it was powered on. Really? Because I do not see any evidence supporting his words. Well, enough talk let us start and get this device fixed.

First things first, I replaced all the diodes, the Mosfet which by the way was P5NK80Z but since I did not have this exact part, I replaced it with P6NK90Z with the same specs but higher in ratings and finally replaced the fuse.

stp60kn90z datasheet

Click hear or the above picture to access the STP6NK90ZFP Datasheet

I powered it through a current limiter and the charger did not come on but also the light on my current limiter stayed dim which means there is no short on board but I still have some defective parts to be found and replaced.

bad fet replace

This is the Mosfet that I replaced and if you look near that you would find a fusible resistor (10 ohms) which I found open and replaced but the charger did not come on.

how to fix a battery charger

You can see the replaced Mosfet and the fusible resister and along that line I also found a faulty current mode controller IC (UC3842B) and replaced it right away.

uc3842 datasheet

Click here or the above picture to access the UC3842 IC Datasheet

shorted uc3842 ic

These are the faulty components (diodes not in photo, sorry) that were replaced in this charger and through a current limiter I powered on the charger and …

how to fix and repair bosch battery charger

Yes, the charger is up and running again and what a delightful sight it was.

I called the customer who came right away because he lives about two minutes walking distance and I could see the smile on his face.

fixing a bosch battery charger

Mission Accomplished.


This article was prepared for you by Waleed Rishmawi, one of our ‘Master Authors’ and currently working in the Bethlehem area of Palestine repairing electrical and electronic equipment.

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Note: You can check his previous article on A Speaker System With Power Issue Repaired



  1. Mark

    February 26, 2022 at 4:57 pm

    Hey Waleed,
    Well done mate! Some people have a strange way of testing components and an even worse diagnostic path. I'm glad you were able to get to the cause of the fault and get it up and running again.

    • Waleed Rishmawi

      February 26, 2022 at 9:11 pm

      Mark: thanks man. it is not the strange way of testing component but the lacking of electronic knowldge and experience to do the repair. have a blessed day

  2. Albert van Bemmelen

    February 26, 2022 at 5:30 pm

    This Bosch charger with the Makita chargers both probably are best quality designs. Most worries though I have is always with the replacement BMS boards for the battery packs that are sold when they do not have any safety temp sensor for the Lithium-ion packs. Luckily I know those BMS boards for the Makita do!

    • Waleed Rishmawi

      February 26, 2022 at 9:17 pm

      Albert: I have opened many battery packs and I found the temp sensors there but these battery are expensive and sometime too complicated to diagnose and very hard to find replacement parts as well but they are high quality batteries and chargers. have a blessed day

  3. Parasuraman S

    February 26, 2022 at 5:45 pm

    A smile of satisfaction from a customer is more important than the money we earn. Good job there, dear friend!

  4. Waleed Rishmawi

    February 26, 2022 at 9:18 pm

    Parasuraman: the smile was priceless and he was very generous in repair fees as well. have a blessed day

  5. Yogesh Panchal

    February 26, 2022 at 10:43 pm

    Hi waleed,
    As said by Albert, i am also agree that most of Chargers do not have OVP or OCP that cause damage to the battery.
    Arranging compatible parts also challenging & Expertise job that you always
    do very well.

    • Waleed Rishmawi

      February 28, 2022 at 2:00 pm

      Yogesh: yes indeed. totally agree with you. have a blessed day

  6. Babu M S

    February 26, 2022 at 11:27 pm

    Very good job done.Learned lot from this repair work.Thank you very much for sharing.

    • Waleed Rishmawi

      February 28, 2022 at 2:02 pm

      Babu: thanks man. I am glad you are getting somethings out of this article and that is an encouragement to me as well. thanks and have a blessed day

  7. Lynn Blakely

    February 27, 2022 at 1:52 am

    Waleed Sir: Another complete repair. I own the same charger, and the Makita also very dependable quality tools. I really believe that both the brands mentioned do have OVP and OVC protection. The Makita is a larger charger and includes temperature monitoring.I love reading all the posts here.

    • Waleed Rishmawi

      February 28, 2022 at 2:03 pm

      Lynn: thanks for your comments. I appreciate it very much. have a blessed day

  8. Tayo

    February 27, 2022 at 5:27 am

    Well done Waleed and thank you for another very detailed article. You have convinced me to construct a more professional looking and capable current limiter than the lightbulb with 2 soldered wires I have siting in my cabinet. The photo the cut diodes shows that many so-called repairmen need to really take their trade seriously. I cant think of a single (innocent) reason why someone would cut or leave them like that. Even someone who has no clue what they are doing would know better than to do that. Oh well... lucky you were there to save the day.

    • Waleed Rishmawi

      February 28, 2022 at 2:05 pm

      Tayo: thanks man and you are most welcome. when any technician loose his passion about repair it becomes just collecting fees to get this done, we go beyond that because the passion of electronics still in our hearts and we aim to please and at the same time we enjoy what we are doing. have a blessed day

  9. jai Etwaroo

    February 27, 2022 at 11:58 am

    Nice job Waleed.

    • Waleed Rishmawi

      February 28, 2022 at 2:05 pm

      Jai: thanks man and have a blessed day

  10. Nilton Cezar Vieira

    March 1, 2022 at 6:59 am

    Hi Waleed.You said: "I took it as challenge...", and you won it with a very professional approach. Thanks for another excellent article.

    • Waleed Rishmawi

      March 1, 2022 at 6:00 pm

      Nilton: you are most welcome. I appreciate your comment. have a blessed day

  11. Steven

    March 1, 2022 at 8:14 am

    Hi can i know how u tested the pmw ic to say its faulty? Do u hv a tester?

    • Waleed Rishmawi

      March 1, 2022 at 6:03 pm

      Steven: common sense. power coming to the IC, charger not powering on, capacitor not discharging, change it and hope for the best. have a blessed day


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