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My computer monitor (Samsung Syncmaster 732N) started to fail and it seems some capacitors have gone bad. They are all electrolitic but one is a CARLI MPX40 .47K275V-X2 capacitor, which where I live (Argentina) turns out is very hard to find.

I didn't know what an X2 capacitor was so I researched a little bit and it seems they are capacitors designed to be used as filters in the power line, and because of that, they have to meet higher standards of endurance regarding temperature, voltage surges, etc. Is that correct?

My question is, suppose I cannot get one of these where I live. Is there a suitable replacement component or circuit that would meet the same security standards? What could happen if I just put a common .47 electrolytic capacitor? Could it blow up or catch fire or something?

Thanks!

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As @Marko implies in his comment, the chances of an X cap failing are very low.

Electrolytics, on the other hand, have a definite lifetime that is relatively short when hot. Presumably you are shotgunning and have limited test equipment- even so you can check the X cap with a regular multimeter. If it measures open on ohms and has close to the desired capacitance it's okay. If you don't have a capacitance range, use the highest ohms range, touch the probes until the meter goes off scale, then reverse them. There should be a short delay before it goes off scale again (because of the capacitance). Anyway, a bad X cap (unless shorted) won't prevent your monitor from operating.

Ideally you check electrolytics with an ESR meter, but you can just replace them all. The biggest ones and the ones close to hot stuff are most likely to be bad (and anything with a suspicious bulge or fluid leakage, of course). Don't confuse the 'gunk' (typically white, off-white or brown) that manufacturers often use to mechanically stabilize through-hole electrolytic caps with dried electrolyte leakage.

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  • \$\begingroup\$ Thanks for your answer! Yes there is a lot of that 'gunk' like you say, but I can see is not leakage, great tip. I have a capacimeter (this one: mco-s1-p.mlstatic.com/1683-MCO4762601003_082013-O.jpg). The X2 cap is rated ".47K275V-X2", is that 0.47uF = 470nF? When I set the capacimeter wheel to the "200n" position and test the cap, it reads "40.2nf". That would mean it went bad, right? \$\endgroup\$ – jotadepicas Aug 20 '16 at 14:27
  • \$\begingroup\$ Yes, it appears to be damaged based on that. The film types (often a yellow box) can be damaged by transients and drop in value. It won't keep your monitor from operating though. \$\endgroup\$ – Spehro Pefhany Aug 20 '16 at 17:33
  • \$\begingroup\$ Thanks! Well, the failure is that the monitor suddenly turns itself off after a couple of seconds. I have a phillips coffee maker with the same failure (see comment by @Tony Stewart in the question) and it is documented that the solution is to replace its X2 cap, so I wonder if in the monitor PSU circuit a faulty X2 could also cause failures, similar to the coffe machine case. \$\endgroup\$ – jotadepicas Aug 20 '16 at 17:47
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    \$\begingroup\$ The capacitors are self-healing and after every 'event' the internal short is burned out, which reduces the value. It's worse if you have bad mains. I've seen it here on motor run caps. I guess you'll know what difference it made (if any) after you replace it. \$\endgroup\$ – Spehro Pefhany Aug 20 '16 at 19:23
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Replacing an X2 capacitor with a non-safety type of capacitor is not recommended. The extra ruggedness built into them are needed when you're dealing with the unpredictable nature of input AC. Furthermore, if you put a non-recognized capacitor in there, plug the monitor in and your house burns down, good luck getting any insurance money.

Failures of X2 capacitors are extremely rare in my experience (when used as an input line filter) - I've been working in the switching power supply industry for more than 15 years and I cannot say I've ever seen one. If you cannot find the exact part, a less dangerous substitution would be another X2 capacitor with the same ratings from a different manufacturer (Panasonic, Elna, Wima, Kemet, etc.)

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The X2 Caps only serve to reduce conducted noise getting back on the line and not to provide power to the unit.

Check voltage capacitance and ESR of each part number and choose equivalent or better.

I believe this is the schematic for input power to your monitor.

enter image description here

Replace the X2 cap if it reads bad with a similar part as deemed necessary. A series choke also reduces inrush currents from external transients.

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