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Blown Toshiba PCX2500 cable modem

Discussion in 'Troubleshooting and Repair' started by voodooutt, Dec 16, 2009.

  1. voodooutt

    voodooutt

    6
    0
    Dec 16, 2009
    i just saw the note on the other repair forum, to post in this forum haha.. so, sorry if double post.

    I'm hoping this modem is salvageable. I grabbed the wrong A/C adapter and proceeded to plug it in. The lights just did a quick blink and I heard a faint "zap". then it was dead. I did not smell any burnt electronics either.

    The proper A/C adapter is a 120-60Hz to 12vDC 1000mA - the one i used is 24VAC 1300mA

    they both look the same, only the labels are different, I'm a little ****ed at myself lol...

    I dont have a multimeter handy either, just off the top of anyones head, what would be the blown component? a simple capacitor?

    thanks...
     
  2. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    Oww..
    Yes, If you're very lucky it could be just a shorted diode (or capacitor) near the input.
    DC devices often have a diode across the input rails that shorts out a wrongly polarized supply.
    If overloaded a diode will short out itself. It could then show physical signs of the abuse, but you may have to Ohm it.
     
  3. voodooutt

    voodooutt

    6
    0
    Dec 16, 2009
    looks as if I have a "Zinc Oxide Varistor" CNR 07D680K across the input rail blue colored
     
  4. voodooutt

    voodooutt

    6
    0
    Dec 16, 2009
    well, i went to the electronics store near me and the guy there basically did not want to help me. I ohm'd it out, and got no resistance, so I would assume its blown..

    so, i did a little research on this item, i really dont know what all these numbers mean, but is there something i can substitute for?

    I found the specs here: http://us.100y.com.tw/pdf_file/CNR-Series.pdf PAGE 4

    Maximum allowable voltage
    ACrms(V): 40
    DC(V): 56

    Varsitor Voltage @1mA
    Min. 61
    Vb(Vdc) 68

    Clamping Voltage @ Test Current (8/20us)
    Vc(V): 135
    Ip(A): 2.5

    Maximum Energy 10/1000us
    (J): 3.6

    Maximum Peak Current (8/20us)
    (A): 250

    Rated Power
    (W): 0.02

    Typical Capacitance @ 1KHz
    (pF): 1200
     
  5. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    Ok, that's an overvoltage/ transient (lightning) protector device. At its rated 40V AC it would not have been affected by the mishap and should measure open like it did. So it seems you'll have to dig a little deeper. What would be the first semiconductor you run into at the input?
     
  6. voodooutt

    voodooutt

    6
    0
    Dec 16, 2009
    hi again, thanks so much for helping me here.

    i took some pics:

    first image: the device labeled "F1" with the number 2 on it is the next inline
    [​IMG]

    second image: "R31" and the black thing to the left are on the flipside of the board, they are also next inline. The solder point just below R31 connects on the other side the the solder point just off to the right of "F1"
    [​IMG]
     
  7. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    F1 is a 2A fuse. I guess this will measure open.
    D1 is a diode. I guess this is ok. It should not measure as a short.
    R31 is a 30 ohm resistor.
     
  8. voodooutt

    voodooutt

    6
    0
    Dec 16, 2009
    ok, so what you're saying here is the 2A fuse is the culprit?

    EDIT: 2 amp fuse is blown. for testing purposes, because i dont have a multimeter, i soldered a wire jumping across the fuse, plugged it in, all is fine. Going to the electronics store to get a new fuse.

    Thanks so much for your help. This is saving me $5 a month from comcast to rent one of their modems... i had forgotten this Toshiba was buried!
     
    Last edited: Dec 18, 2009
  9. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    That's great news! :)
    If they don't have smd fuses you can always fit a (small) wire-ended fuse.
    Doing without the fuse is of course possible but will put something else at risk if something ever happens.
     
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