re-attaching a broken stepper board capacitor?

I have very little electronics or soldering knowledge and I had just managed to do all the RepRap style mods to pre-built MakerBot boards and was mounting the boards onto my Mendel when my pliers slipped off the damn nylock nut and half knocked a capacitor off a stepper board. There's a scratch on the side, but I think it's ok. One lead totally detached and the other is loose. Here's a picture: [www.flickr.com]

Does anyone have some advice on how best to fix it? Also, if I do manage to re-solder the tiny leads (I just ordered a smaller iron tip yesterday, I'll probably need it) how would I go about testing to make sure it's reconnected using a multimeter? Or should I just hook it up and see what happens, could it damage anything?

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Tony Buser http://tonybuser.com * http://reprap.org/wiki/User:Tbuser#Projects

Hopefully the trace pad did not lift from the board. If that happened then you would need to run a wire back to the common point.

Typically with these I use two irons. Since one side is already off then you can heat the other and remove the cap.

Testing a cap requires an analog volt meter with a needle. Set the volt meter to the resistance scale. This works as there is an internal battery which provides current. When the cap charges the voltage drop changes and the needle swings (Why an analog meter is needed.) It takes some practice to understand the swing. Normally this voltage drop is read as resistance. The cap has to be isolated from the circuit for this to work.

If the pad has not lifted, then one can re attach the cap soldering each pin at a time. Usually there is enough of a lip for hand soldering on most components.

If the pad has lifted, It probably would be easier to replace the SMT cap with a leaded cap. One would have to trace back to the common points. Most likely this is a filter cap which connects across the supply.

I can't tell if the pads are on the board or pulled up against the leads, but I turned it to the side a bit to try and get a better look underneath and took two pics:

[www.flickr.com]

[www.flickr.com]

Click on the all sizes link to see a better view... It looks like the one side pulled part of the trace on the board loose?

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Tony Buser http://tonybuser.com * http://reprap.org/wiki/User:Tbuser#Projects

looking at the board if you can't reattach this capacitor you could hook one with leads up right at the power input to the board (in the screw connectors). I would assume that it is used just for filtering the power coming to the board. I'm not an expert and would check the schematics.

The photograph makes it look like the green FR-4 substrate is where the pad should be.

From looking at the online documentation that these are power filter capacitors. So you should be able to get one with leads and connect it between ground and power. These are placed close to the connector to be effective.

I am not using this board in my setup (a mix of Gen 2 stepper drivers and the Gen 3 Sanguino.) so I can not be absolutely sure. I tend to use smaller caps closer to the chips in my own layouts. Something I notice not done on the v1.2 sanguino board.

I think I managed to reconnect it by trying to add a bit of solder to the exposed pads then holding it down while pressing the iron to the tiny exposed leads on each side. I tested it by using a multimeter to check continuity between power/ground and the appropriate exposed leads of the capacitor. I guess I'll know if it's right once I get a cable made to hook it up... I'm still a little worried that I might damage something hooked up to it if it's bad? I don't have an analog meter to test it like sheep said.

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Tony Buser http://tonybuser.com * http://reprap.org/wiki/User:Tbuser#Projects