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Makita charger diode

Discussion in 'Troubleshooting and Repair' started by timshrub, May 22, 2010.

  1. timshrub

    timshrub

    13
    0
    May 22, 2010
    Hello all. I'm trying to repair a makita battery charger and need to identify a diode.
    Diode is marked as either 16N8H or H8N91 not sure which. Any help would be very much obliged. Thanks
     
  2. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    I have even more questions for you than you for us; why do you think it's a diode, and why are you not sure which? That kind of numbers may also be found on MosFet's.
    Does it say diode on the PCB? A picture or a better description might help us help you.
    Either way one of the numbers may be the Amps and the other number may be the Voltage (less a zero).
     
  3. timshrub

    timshrub

    13
    0
    May 22, 2010
    Hello Resqueline
    Thanks for the reply. Its definitely some kind of diode, the pcb is clearly marked with the diode symbol and the component is labeled as 'D5'. It has a black plastic case marked at the cathode end with a silver ring, the numbering is also in silver. I thought diode codes always started with '1N' ? Obviously not, they don't make it easy for us newbies!
    Hope this helps, thanks again.
    Tim (timshrub)
     
  4. timshrub

    timshrub

    13
    0
    May 22, 2010
    By the way, its 3mm long and 2mm in diameter.
    Thanks
    Tim
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Here are some diode symbols. Which one is it?
     
  6. timshrub

    timshrub

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    0
    May 22, 2010
    Hello Steve
    None of those actually! Sitting here looking at the pcb, the symbol looks a bit like a capital 'M' with long legs. Now I've looked a bit closer, all the other diodes (some of which are definitely run of the mill glass germanium diodes) have a symbol which is a white rectangle with a white bar at the cathode end. Probably means this is something a bit more exotic, right? I'll try and take a picture, just need to work out how to post it.
    Thanks for the reply.
    Tim :)
     
  7. timshrub

    timshrub

    13
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    May 22, 2010
    d1.jpg

    d2.jpg

    Here are two photos, one of the diode in question, and one of the symbol on the pcb (marked D5, next to the burn mark....)
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,191
    2,693
    Jan 21, 2010
    Does the diode still have diode action (i.e. are you sure it was dead?)

    If you can photograph the opposite side of the board then we may be able to discern the function of the diode and suggest a plausible replacement.
     
  9. timshrub

    timshrub

    13
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    May 22, 2010
    d3.jpg

    Here's a shot of the reverse side of the pcb with the diode mounting holes about in the centre of the frame.
    The diode was tested with a dmm with one of the leads removed and showed almost equal resistance in both directions. As I understand it, diodes of any type should exhibit very high resistance in one direction. The diode has also been so hot as to burn a groove of its own shape into the material of the pcb.
     
  10. timshrub

    timshrub

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    May 22, 2010
    None of the brown staining caused by overheating was due to me by the way.
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Here is a composite image that may help.

    I don't think there's enough of the component side visible though.
     

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  12. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    D5 is part of the R4, R5, C5 snubber circuit. They are there to take the top off the switch-off voltage on the main power transistor to protect it from breakdown.
    You can replace it with any high-speed high-voltage switching diode. 1A & 600V should suffice, switching speed should be as low as you can get. Size doesn't matter.

    The M-shape of the symbol is just due to the hole for the pins cutting off the silkscreen print. It should be same shape as on all the other diodes there.
    Oh, and glass diodes are not by definition germanium. No germanium diodes have been made in the last 40 years. You probably meant small-signal switching diodes.
     
  13. timshrub

    timshrub

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    May 22, 2010
    Hello Resqueline
    Thanks very much for the advice, now I can proceed. As I said, I am just a beginner and there is absolutely no substitute for experience and knowledge, which I obviously lack.
    Very much obliged.

    Thanks also to you, Steve, for your contribution, things sometimes seem a bit hopeless when you don't know anybody you can ask about these things.

    Tim
    Denmark
     
  14. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    You're welcome, glad to be of help. I was in your position once too you know.
    When I mentioned low switching speed above I was thinking low numbers [us]. When/ if you locate a probable replacement please get back to us.
    Steve, you seem to have too few tasks at hand.. ;) I'm impressed you actually did a composite image.. Wow! :D
     
  15. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,191
    2,693
    Jan 21, 2010
    Actually I'm off to the US in a week or so and I'm as busy as a one armed paper hanger.

    Just spending a few moments here from time to time...

    It was pretty rough, but I hope it helped.
     
  16. timshrub

    timshrub

    13
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    May 22, 2010
    Hello again
    Regarding the replacement diode for this makita charger I'm working on, I've found various suitable replacements on the internet. They all seem pretty beefy compared to the faulty component but otherwise have the required specs. As far as the switching speed goes I'm not really sure what to compare with. How low is low?
    Here's what I found, what do you think?

    Fairchild RHRP3060
    NXP BYC8-600
    Diodes Inc. RL205-T
    Fairchild RURG3060
    Sanyo RD2004LS (400V 20A)
     
  17. timshrub

    timshrub

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    May 22, 2010
    Just found some more which fit the Current/Voltage requirements but there is no mention of them being a switching diode. What makes a switching diode a switching diode?
    Thanks
    Tim
     
  18. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    RHRP3060 & RURG3060 are 30A, way too big to fit & certainly costly.
    BY8C-600 is 8A & hyperfast (30 nanoseconds), also quite a bit overkill.
    RL205-T is a 2A standard diode. At least it'll fit, but don't go for a standard one.
    RD2004LS has marginal voltage and total overkill current.

    I they're not mentioned as being switching devices then they're not. Reverse recovery times below a microsecond starts to be useful.
    Look for terms like fast, superfast, ultrafast, & hyperfast. That's the order of their rated "speediness". And there's no need to go much over 1A, better to up the voltage.

    How about choosing a supplier first and see if they have something useful. Being in Scandinavia you may have easy access to Elfa. Check them out if so.
     
  19. timshrub

    timshrub

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    May 22, 2010
    Thanks Resqueline, I'll have a closer look.
     
  20. timshrub

    timshrub

    13
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    May 22, 2010
    Finally! I think I've found a suitable diode. This was after working out that some manufacturers refer to them as 'Fast Recovery Rectifiers', this gave a few more hits on Google.

    The diode is 1N4937, seems to fit the bill, what do you think Resqueline?

    Thanks
    Tim:)
     
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