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I just bought my Arduino Ethernet shield – a knock-off one for $10 instead of $60. I connected it up, but it doesn’t work – LEDs light up but do not blink, and no ethernet link is established (ethernet switch doesn't light up, can’t ping, etc.). It’s as if the Arduino cannot communicate with the board.

Trying to work out why, looking closely it appears as if the soldering on the Wiznet chip is messy, and a few sets of pins are bridged. Is this potentially the source of my problem, or could this be done on purpose?

Angle view of Wiznet 5100 chip with solder bridges Top view of Wiznet 5100 chip with solder bridges

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    \$\begingroup\$ I suspect that you've found the reason that it was $10. \$\endgroup\$
    – markt
    Feb 20, 2015 at 6:21
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    \$\begingroup\$ I have seen a number of FTDI boards where the designer forgot the reset pin and solder bridges were added purposely. This is hardly best practise though. \$\endgroup\$
    – David
    Feb 20, 2015 at 8:26
  • \$\begingroup\$ Ooh, this looks like my soldering! (sigh) \$\endgroup\$
    – Greg d'Eon
    Feb 20, 2015 at 13:23

4 Answers 4

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In the old days of DIPs, sometimes entire sides of chips were designed as heatsinks, so it made sense to connect them with a big blob of solder too. But this heat-sinking technique is extremely uncommon for SOPs, which usually use pads underneath the package when moderate heat-sinking is needed. (Before someone says that using pins as heat-sinks is nonexistent for SOPs, the SO8 version of OPA551 uses a couple of [non-adjacent] pins as heatsinks).

As for your chip, Wiznet W5100 (which alas I first read as WS100 making me waste some time) there's a datasheet for it; it seems the guys who put together that PCB soldered together most if not all the address pins, which couldn't possibly work.

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  • \$\begingroup\$ Thanks – I never thought of that use! But yeah, it’s obviously not what’s happening here. Time to return it as faulty… \$\endgroup\$ Feb 20, 2015 at 7:35
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    \$\begingroup\$ You can try "wicking" the solder bridges out. That might solve the problem. You can always return it if it does not. \$\endgroup\$
    – Guill
    Feb 28, 2015 at 8:25
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I think that you may have found your problem. Cure is fairly easy - all lots of liquid flux on top of all those solder bridges and either drag the excess solder off with a hot, clean soldering tip or use solder-wick to suck up the excess. I usually clean the board afterwards - if you use Rosin flux, a toothbrush and IPA works well. Use enough IPA to wash all the flux off the edge of the board.

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    \$\begingroup\$ Since he powered it up already, I wouldn't bet on this being salvageable just by removing the bridges. He didn't say that anything went up in smoke, but I've seen plenty of shorts killing chips without any fireworks. \$\endgroup\$ Feb 20, 2015 at 7:11
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    \$\begingroup\$ Good to know I’m on track. I found this Youtube video showing how to do this as you describe – youtube.com/watch?v=eg2hxpy--gg – I might give it a go when I get time. \$\endgroup\$ Feb 20, 2015 at 7:41
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    \$\begingroup\$ I would rather send it back for a refund right away than attempting a repair. By repairing it, you will essentially void any warranty and lose your rights for a refund. If you had already powered up the device, there's a chance that the device is already broken beyond repair (see comment of @RespawnedFluff). \$\endgroup\$
    – shimofuri
    Feb 20, 2015 at 23:21
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It has already been said that these bridges should not be there. This can also be seen easily on the left side (lower picture), as the short but thick trace connects to only three pins. If all pins should be connected together, there should be tracks to each pin.

About general design of PCBs, a colleague of mine used to connect several pads in a row by a single track through all pads. As the result looks like solder bridges, it was indistinguishable from them. I would never do so, but always connect the pads at the side of the pad row. Then, any solder bridge found is clearly an error and should be removed.

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That is surely the problem. They may have reflowed the solder joints, and not fixed the pins later. However, it may well work if you fix it; try Dwayne Reid's solution

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