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I was experimenting with my universal laptop adapter (Meind 100W) and when I switched it to 34V mode (while official max is 24V) the capacitor (25V) popped (the top opened and some white fibers spread over the nearby parts).

The capacitor is glued to the board and is not easy to remove. When using the adaptor it slowly heats now.

When under load the output voltage of the adapter drops (and probably recovers after some seconds), so I have to set it to voltage that is higher than needed.

Questions:

  1. Is it safe to continue using that adaptor? Can it degrage further with time or it will remain stable?
  2. How to unglue the damaged capacitor from board?
  3. Should I use some additional safety measures (for example, external capacitor connected to output) to reduce the risk? (I'm not going to just buy another adaptor)
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  • \$\begingroup\$ It seems to work worse and worse. Stopped using it in favour of old and big one. \$\endgroup\$ – Vi0 Feb 12 '11 at 3:05
  • \$\begingroup\$ Repaired it with a pair of capacitors soldered from old defunct laptop adaptor. Now it works. \$\endgroup\$ – Vi0 Feb 20 '11 at 18:08
  • \$\begingroup\$ BTW the popped capacitor still works (although internal resistance is much higher) \$\endgroup\$ – Vi0 Feb 22 '11 at 1:14
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Most likely the popped capacitor is causing stability issues (output going up and down as you described).

It should be replaced with a part with comparable voltage, ripple current, ESR and life ratings. Failure to choose an appropriate cap will likely result in the cap failing prematurely.

A properly protected power supply should not be damaged from a blown output capacitor. I wouldn't recommend operating it until the cap is replaced.

It seems odd to me that the power supply is capable of self-damage. With 25V caps the max output ought to be below 20V.

I would use a sharp utility knife to cut the part from the glue, then desolder it and replace it. Make sure you note the polarity.

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  • \$\begingroup\$ It seems odd because I used hacky mode: switch is set between "22V" and "24V" => both 22V and 24V LEDs are on and output is 34V. (BTW this power adaptor is in general considered unsafe). Currently powering my laptop from it having connected additional large capacitor in parallel to laptop, but the voltage seems falling and falling. \$\endgroup\$ – Vi0 Feb 12 '11 at 2:39
  • \$\begingroup\$ Is the blown capacitor the only one on the output? Most converters that I know of won't work at all without a capacitor. \$\endgroup\$ – Adam Lawrence Feb 12 '11 at 3:17
  • \$\begingroup\$ I expect that blown capacitor still works (reduced). For example, adaptor's LED fade out slowly (not abruptly) when it is plugged off from mains. (There are also other, smaller 25V capacitors in other parts of circuit). \$\endgroup\$ – Vi0 Feb 12 '11 at 3:51

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