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Re: How to open a Dell Power Supply/Charger

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On 8/29/2012 12:15 PM, davy wrote:
> To open molded cases I uses a Dremel mini tool with either a cut off
> disc or s mini saw blade, works a treat, take it easy running along the
> seam... expect plastic dust so watch your eyes.
>
> I usually Araldite them together afterwards leaving them held in a clamp
> for a few hours.
>
> I don't know about Dell, but the things I've repaired are usually either
> switched mode power supplies or the good ol' wall warts with a
> transformer, some are heat molded and yet some may have screws in the
> base, usually concealed.
>
> The switch-mode variety is usually capacitors that need replacing,
> you'll see them bulged at the top or leaking gunge, which must be
> cleaned off as it's very corrosive...
>
> or they are usually blown to bits making repair not possible. What
> happens here, is the capacitors fail, thus the feedback loop from the
> isolated side to the live switched side goes ballistic, so the poor
> transistor switches ON harder and harder until it self-destructs causing
> major damage... this loop maintains regulation by altering the switching
> drive's mark space ratio.
>
> Always use *low ESR 105 deg. C* type capacitors should this be the case,
> don't be tempted to use standard 85 Deg. types in switch-mode power
> supplies.
>
> Another way to open them is to use a fine hack saw.
>
> DO REMEMBER INSIDE THESE SWITCH-MODE SUPPLIES THERE ARE LETHAL
> VOLTAGES[/B] UNLIKE THE TRANSFORMER VERSIONS (AC LINE VOLTAGE X 1.414)
> SO IN THE UK  WHICH IS AROUND 240V AC X 1.414 = APPX. 340V DC!!!!! [B]SO
> ENSURE IT IS UNPLUGGED FOR ABOUT 5 MINUTES.
>
> davy
>
>
While that's all very true in general, in particular, for this supply,
the symptoms suggest one of the two primary failure modes related to user
abuse.
1) the solder joints at the AC input fracture where the socket solders onto
the board.
2) the output cable gets shorted or open from repeated flexing
at the box or at the DC output plug.
If it's intermittent, you can often tell which end by flexing while
it's running.

I used to use a TDR to figure out which end was open until I realized
that if the cable decided to reconnect while I had the TDR hooked up,
and there was any charge on the caps, I'd blow up a TDR that originally
cost more than my house.
With technology these days, you can do the same thing with an ordinary
bench pulse generator and scope.

I don't understand this:
The AC wall cord is still in excellent condition, and except for the
strain relief allowing the braided conductor to show through, so is the
output cable to the computer. The P/S is the PA-9 type; 20V, 4.51A,
model PA-1900-05D.

The PA-9 on my 5100 has the standard 3-pin socket at the AC input.
The strain relief and shield that can show thru is on the DC out end.

If the shield is broken, I've fixed 'em by soldering some wires across
the broken part and "potting" the area in hot-melt glue.  But you have
to be very careful not to flex it much after that.

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Thread

How to open a Dell Power Supply/Charger Ki_Image <Ki_Image.5i1h2h@no.email.invalid> - 2012-08-28 20:46 -0500
  Re: How to open a Dell Power Supply/Charger mike <spamme9@gmail.com> - 2012-08-28 20:49 -0700
  Re: How to open a Dell Power Supply/Charger AaronL <135sdf6738@fakiemail.com> - 2012-08-28 21:01 -0700
    Re: How to open a Dell Power Supply/Charger richgr@panix.com (Rich Greenberg) - 2012-08-29 15:53 +0000
    Re: How to open a Dell Power Supply/Charger davy <davy.5i3f5b@no.email.invalid> - 2012-08-29 14:15 -0500
      Re: How to open a Dell Power Supply/Charger mike <spamme9@gmail.com> - 2012-08-30 03:25 -0700
        Re: How to open a Dell Power Supply/Charger Couturier946 <Couturier946.5ji0pp@no.email.invalid> - 2012-09-26 03:46 -0500
          Re: How to open a Dell Power Supply/Charger mike <spamme9@gmail.com> - 2012-09-26 10:05 -0700
      Re: How to open a Dell Power Supply/Charger Ki_Image <Ki_Image.5i3zpg@no.email.invalid> - 2012-08-30 00:54 -0500

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