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I have a board with two super low ESR SMD electrolytic capacitors which came off the switching power supply of a notebook motherboard. The legs of the capacitor are still soldered on the board. One of them has a capacitance of 47uF, the other of 560uF.

With both, I have managed to create two sort of legs by soldering two wires in place of the original legs.

In order to restore the capacitors onto the board I need the jumper wires to be a bit longer than the original legs (some 2-3cm each).

My question is: would this extra length in the connection cause trouble in the circuit? Would the parasitic inductance / capacitance generated be low enough that I get away with this fix in both cases?

Please find below the relevant pictures: Section of the board with capacitor fallen off

Capacitor with missing legs fixed with jumper wires Please let me know. Thanks.

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  • \$\begingroup\$ Could you include a photo of the situation? \$\endgroup\$ – uint128_t Feb 17 '16 at 16:37
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    \$\begingroup\$ I'm confused. 1. you identify both boards as "the board" 2. Is the picture of the board the one the caps came from or the one the caps are going into? 3. If it's the one the caps came from, why is that at all relevant, and if it's the one the caps are going into why do you need one inch leads on the cap(s)? \$\endgroup\$ – EM Fields Feb 17 '16 at 17:41
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    \$\begingroup\$ @geraldCelente the 560uF is almost guaranteed to be an "energy storage" cap, thus operating at near DC (560uF/0.56mF is actually a huge cap for anything short of a supercap) potential, so it shoud be affected about 12 times less than the 47uF one. Would trying hurt? Most likely it won't, cause any 'permanent damage.' Assuming that they're most likely power-supply reserve capacity/fitering capacitors, the worst 'likely case' scenario is that a bit of noise wil "sneak past" and cause errant performance of the lappy (unlikely), in which case you can shorten the leads, then try again. ;-) \$\endgroup\$ – Robherc KV5ROB Feb 17 '16 at 18:10
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    \$\begingroup\$ (P.S.) The one danger I do however see, is that your caps may have already become damaged & could catastrophically fail due to pre-existing damage now. In which case, they may either A: fail entirely to do their job, and allow huge transients onto the rest of your ciruit, or B: Short/arc & potentially fry your power supply (or whole motherboard) by providing a "DC short" from Vcc to GND through the failed capacitor. \$\endgroup\$ – Robherc KV5ROB Feb 17 '16 at 18:13
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    \$\begingroup\$ When you said "came off" I took that to mean that you had removed them for some reason. If they came off of their own volition, throw them away, order the proper replacements, clean up that mess on the board and solder in the new caps. @Asmyldof is spot on on this one. \$\endgroup\$ – EM Fields Feb 17 '16 at 18:21
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Will wire unequivocally add too much ESR or inductance to the whole? No.

In many situations, such as bodge-testing a beta design with more capacitance, a tiny bit of wire of the appropriate diameter will only add several or tens of miliOhm to the total resistance and usually inductance is limited.

However, should you use this solution of yours? No again.

Or to put it in terms of an answer to one of your latest comments:
Actually ordering the original replacements and waiting for them, on the other hand, will save you the potential hassle of buying a new laptop.

Why?

A capacitor of which the legs break is not to be trusted. Those legs are spot welded (or whatever they use as a process the last few years) onto the alu-foil, so the torsion is likely to misalign aluminium foil or even short it or warp the stack-up, before the leg breaks.

This can have detrimental effects to any one of the specifications, if not all of them. A 5% to 10% error in most specifications should be allowed in the design, if the designer understands his actual job. An error of 10% in all of the specs, or a 40% error in one, on the other hand, is a whole different story.

Look at it like this: If you order the caps, put them in without destroying anything else and then it works again, you spent 3 days waiting and a buck or three. If you do it like this you have a chance of being out an entire laptop in trade for 3 days quicker. In which case those 3 days won't have made a damn of a difference on the following decades of no laptop.

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