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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 27th May 2018, 5:42 pm   #41
WaveyDipole's Avatar
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Default Re: What to replace a RIFA X2 with?

I appreciate the comments. I will get rid of those RIFAs as per my first instinct and replace with the types suggested.

Originally Posted by Argus25 View Post
I'm afraid that the only way to properly re-cap a vintage switch-mode psu is to take note and document every single electrolytic in it from the supply itself & the schematic, uF capacity and voltage and physical geometry height and diameter where important and radial lead spacing, then sitting down with something like the RS or Farnell/Element 14 catalog, patiently selecting suitable 105 deg C rated replacements, preferably items like Panasonic or Nichicon brand low ESR types (designed for SMPS use), and replace the X2's while you are at it.
From what I have learned from these forums, which are a wealth of information, this is what I was beginning to think. For SMPSUs I only now use Panasonics, Nichicon or Rubycon with the same or nearest higher voltage rating, 105deg low ESR types. I think this has convinced me to replace the remaining caps while I am in there.

Originally Posted by Argus25 View Post
If you buy a "kit" somebody else has assembled, you are only likely to get part of what you really need and there is no guarantee of the origin/quality of the replacement caps. Likely they will be the cheapest option, which is exactly what you do not want for a SMPS. So you have to take on the task of assembling your own capacitor kit for the job yourself and not rely on another party, or these are the kind of disappointments that wait in the wings. You are not alone, I have been through this myself. I once bought an expensive capacitor kit for a valve amp refurbishment, many were not suitable, missing and wrong values and poor parts, I only used about 10% of them in the end.
Makes sense. The kit is minimalist, and cheap enough to be offered as a freebie (as indeed it was to me), perhaps as an inducement to purchase? It is unfortunate that someone not sufficiently clued up might feel that once they have installed the kit the job is complete so they are lured into a false sense of security. Although it omits the other 9 capacitors, the kit includes an exit grommet for the mains cable, a few cable ties and a short length of red, green and blue heat shrink, but no instructions. Since all mains cables are already insulated (as they should be), the latter made me think that they are perhaps meant for recovering cut and re-soldered mains cables. Yet it is possible with care, to remove the board without cutting or damaging anything at all.

I guess if the mains cable is replaced then the new grommet would be useful, which leads me on to another question (sorry, my original concern was the RIFAs and this is moving away somewhat from that topic although still related to the same PSU) regarding something I have not yet though about: if the cable looks perfectly OK, should I leave it alone, or replace it as per routine maintenance? Unlike perished rubberised, fibre bound and gone brittle PVC cables of the past, modern mains flex doesn't seem to deteriorate over time. Or does it?

Last edited by WaveyDipole; 27th May 2018 at 5:50 pm.
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Old 27th May 2018, 10:28 pm   #42
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Default Re: What to replace a RIFA X2 with?

Originally Posted by MrBungle View Post
Everything has a design lifetime. Planning that is part of engineering.
But if you're building something for yourself, not to a design done to appease beancounters, that design lifetime is "forever".

If you are going to have to replace a capacitor eventually, you should account in your design for the fact that you probably are going to have to do it more than once. Which might mean having the PSU filtering components on a separate board, so it can be exchanged as a module and repaired at leisure.
Julie {formerly known AJS_Derby}
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Old 28th May 2018, 12:07 am   #43
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Default Re: What to replace a RIFA X2 with?

Originally Posted by Maarten View Post
While I do to some degree agree that X2 capacitors break down at transients, that is not the normal mode of operation only the normal mode of failure. A cheap polyester one is more likely to exhibit failure than a polypropylene from a more reputable brand. As Station X says, a non-X2 polypropylene of a sufficient rating just won't fail (but has a minor chance it will fail a bit more destructive if it ever fails).
I forgot to add something here. Some manufacturers carry a series of X2 capacitors that is especially rated for use as a series capacitor in mains supplies. Those are constructed in a way that makes it especially unlikely to fail by excessive self-healing caused by transients.

Some equipment manufacturers ignore this particular faillure mode, causing something that is in The Netherlands known as 'senseosyndroom' (senseo syndrome). Named after the quite popular coffeemaker that often exhibits this faillure mode prematurely when used in 'rough' environments such as near inductive kitchen equipment.
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