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Zener diode question

Discussion in 'General Technical Questions and Answers' started by WF7A, Jun 20, 2019.

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  1. WF7A

    WF7A Subscriber QRZ Page

    Howdy, howdy.

    Admittedly, zener diodes weren't covered much in my formal electronics education so I'm stuck with finding a suitable replacement zener (switching) diode to replace in my stereo's subwoofer's power supply, but I'm not sure what to buy/order.

    It's a Boston Acoustics MCS-160. Here's a vid of one guy who fixed his using a 1N914 1N4148: (at the 1:58 mark)

    Here's the link to Radio Shack's store with the part he used:

    ...but on, someone repaired his unit with a different spec that calls for 18V, 500mW:

    I looked on Mouser's website and couldn't find an appropriate part so what should I look for or what would be an appropriate substitute that I can order either from Mouser or somewhere else?

    TIA or your help!

  2. K7JEM

    K7JEM Ham Member QRZ Page

    A 1N4148 is not a zener diode, and not a replacement for a zener diode. What you are looking for is apparently a 500mW 18v zener. They are available at Digi-Key and probably every other place that sells electronic parts. It is a 1N5248B or equivalent. Available for 14 cents each:

    Without actual troubleshooting, it is hard to say if this is the problem. The shipping will be around $5. At Digi-Key you can specify USPS first class mail on small or very light orders, I just ordered a 31 cent capacitor with $5 shipping, but UPS was a couple of dollars more.

    Here is a US seller on e-bay that has 20 of them, delivered to you for less than $5:!85546!US!-1

    Mouser has them for 13 cents, but I don't know what their shipping is:
    WF7A and WQ4G like this.
  3. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    Find out what the diode actually is, zener or switching diode.

    I have a stock of all kinds of zeners and switching diodes so if you need one it's yours for postage.

    KD8DEY, WQ4G and K6LPM like this.
  4. W5RKL

    W5RKL Ham Member QRZ Page

  5. KA9JLM

    KA9JLM Ham Member QRZ Page

    A Zener diode is just a bad diode with a low break over voltage. o_O

    Find out what you need Rich. I can mail you one for free, If I have the one you need.
    Last edited: Jun 20, 2019
    KD8DEY likes this.
  6. WQ4G

    WQ4G Ham Member QRZ Page

    Be wary of Zeners purchased from ebay. Some sellers are selling counterfeit parts. I purchased a couple of NTE 144A, which are supposed to be 14v Zeners, and received 15v Zeners.

    The Zeners I received were in what appeared to be an authentic 'NTE" package but were not NTE parts. What made me think they were counterfeit was A) They were not 14v Zeners B) Markings on Diode were not legible C) The packaging, while close, did not match authentic NTE packaging. The markings on the diodes were so smeared up that it was difficult to see the cathode stripe.

    Let the buyer beware....

    Dan KI4AX
  7. WF7A

    WF7A Subscriber QRZ Page

    Thanks, guys! I really appreciate your generous offers and great info. I'll gladly pay for postage--and will include some extra doubloons--for your troubles.

    I've been scouring the 'net looking for a schematic (since one won't be forthcoming from Boston Acoustics) so I can't definitely determine what kind/part number the diode is, but I suspect that since it's being used in a power supply and possibly regulating voltage/ripple, that it's a zener and not a signal diode.

    I'm taking today off from work as a "mental holiday" so I'll unsolder the old diode to see if I can read its part number (which I can't do until I remove it. Even I know that it's bad manufacturing practice to have most/all of a part number facing the board, not the air.) I'll be sure to mind the polarity of it, too.

    *waves removed diode by my ear as if keeping to a musical beat*
    The Wifoid: "What are you doing?"
    Me: "Listening to the band. Nyuk nyuk nyuk." (Stole that joke from Curly of The Three Stooges.)
    KA9JLM likes this.
  8. AA7EJ

    AA7EJ Ham Member QRZ Page

    I am not so sure one has to go to all that trouble REPLACING any component which has accessible LEADS.
    Just clip the leads at the BODY of a diode and solder the replacement to the existing wires.
    Of course do not use excessive heat to accidentally unsolder the original leads.
    Actually diodes seldom go short, so just soldering the new one on top of the burned out one would also work.
    73 Shirley
  9. WF7A

    WF7A Subscriber QRZ Page

    Good suggestion, Shirley--I'll clip the diode from the board to get its info, but it would be easier for me technique-wise to solder the new part with its leads through its respective holes; these old eyes aren't as good as they used to be and including the limited room to maneuver around parts and such, it would be easier to wield a soldering iron from the solder side of the board.

    I know this is "shotgun" troubleshooting, which isn't very professional, but seeing that this diode seems to be a common failure point, having no schematic or diagnostic equipment other than a VOM, and that it's a cheap seems like a logical approach to replace it.

    *opens an envelope and is happy to see a replacement diode in it*
    "Myyy zener." (Ya gotta say that just right for full effect.)

    On edit: Just clipped the diode but it's so small that I can't read the part number, even with my magnifying glass. I'll have to find a microscope somewhere. : S
    Last edited: Jun 20, 2019
  10. WR2E

    WR2E Ham Member QRZ Page

    The 'hammy hambone' way.
    KS4W, KA1SHU, WQ4G and 1 other person like this.

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