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So I go to the thrift shop around the corner, and I'm met with these two boxes in the electronics' section:

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I'm sifting through these one by one, tangle by tangle, searching for a power adapter that conforms as close to what I expect. Alas, I find a MOTOROLA SPN5202B, which has the wrong fitting, and is just shy of some characters that match the SPN5504 model in the listing:

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Nonetheless, the OUTPUT settings are identical. I continue searching one by one, tangle by tangle, and I come across something interesting:

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Naturally, I plug it in to see if it fits:

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It fits... Now, what I'm thinking is that I can just connect these two together--cutting some wires and taking the fitting from the latter to replace the fitting of the former. However, I'm also thinking how I don't feel like waiting for another Raspberry Pi from Amazon if I mess it up, so I'm wondering how exactly I can be sure that this is possible. I don't have a multimeter, but I can use my university's laboratory equipment.

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  • it's much cheaper in terms of time and money to buy the correct power supply instead of spending time tinkering with a great chance to permanently damage the board. – lenik Nov 22 '13 at 4:20
  • Buy a multimeter for the love of Raspberry Pi! PS Good buy :) Have fun. – Piotr Kula Nov 22 '13 at 16:43
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    The only thing you could have done wrong (that has any potentially bad consequences) is connect the 5v of the adapter to the ground of the usb-plug, and also vise versa. Small chance, as wires are color-coded. Just plug in the Pi, check if the red led lights up, if not unplug immediately. The Pi does have some reverse polarity protection in the form of a TISP diode. – Gerben Nov 22 '13 at 20:16
  • Or just stick an led into the usb plug, to test the polarity. – Gerben Nov 22 '13 at 20:16
  • So, I just opened the auto charger, and the pink and green wires are attached to the board with the symbols U+ and U- next to them respectively. I linked them together and connected it to the Raspberry Pi really quickly. The PWR led turned red. What does this mean? I didn't have anything else plugged in. – Trancot Nov 26 '13 at 7:02
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Yes, I have done this sort of thing several times and I am no electronics expert. You have to be quite sure that you have the polarity right and that everything is fully insulated.

I buy two heat shrink tubes, one larger and one smaller. Then I cut off both barrel connectors making sure that the one you intend to use has enough wire to work with.

Now slide about 4cm of the bigger shrink tube over the wire towards the barrel. Cut back some of the outer insulation near the cuts and slide on about 2.5cm of the smaller shrink tube over one side of the positive wire. Join the two positive wires then cover the exposed area by sliding over the tube and apply heat (I hold it over a gas cooker flame for a couple of seconds, repeat as necessary) until it is a tight fit. Repeat the process for the second wire. At this stage check that the connections are good and the polarity is correct,

Now slide the bigger tube over the two tubes that are now shrunk and apply heat. Job done but check the polarity again before you plug it into anything expensive. Maybe you should have a trial run with the parts you plan to discard.

Two final points: The voltage of the new power cube must be the same but the amps can be higher. For running a RPi 800mA should be enough but a bit more never hurts.

Get a multimeter, a basic one is very cheap. You need it to check the polarity and it is a very useful tool to have lying around.

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