RIFA X2 250V Line Filter Capacitors in Amiga PSUs

[dalek]

Not sure if this is common knowledge here, but at least the BBC micro folks have figured it out. If you google "rifa x2 capacitors smoke" you'll see what I mean

The RIFA 250V Line Filter caps in at least the A2000 Eltek and A1000 Mitsumi power supplies can start to smoke and fail (failing open - so there is no longer noise suppression on the AC side).

On the A2000 Eltek PSU, this X2 cap is hidden in the heatshrink that covers it along with the Y Caps that are soldered directly to the IEC socket! So they can be easily missed and can have failed without you even knowing it (except for the horribly rotten smell).

Here are the failed ones:



And here is one that hasn't failed yet from my A1000 PSU - you can see there are 'cracks' in the paper which means it is starting to fail. It also has some Y caps I'm going to replace too.



Here in Australia the mains voltage is 240V AC which is not far from the max 250V rating of these caps. I understand the EU mandates 275V for these caps which is what I am going to replace them with!

Unfortunately in many "capacitor kits" that are bundled for Amigas out there they do not include the X2 caps.

With the X2 cap blown the PSU still appears to function normally if it blows open but EMI noise can be fed back through your mains circuit. Not sure what effect this has on the low voltage side if any.

[Daedalus]

Some good advice, but I thought I'd point out a couple of things. Most capacitor kits are for the Amiga itself, not the PSUs. Since there are many different versions of PSU even for the same models, supplying capacitor kits for PSUs isn't very practical. Most people prefer to just replace the entire PSU circuitry with a more modern (and more efficient) version.

As you say, these caps aren't critical for normal function if the electricity supply is relatively clean. A more pressing issue IMHO are the large smoothing capacitors in the PSUs which, at this stage, have had decades of hard work with high ripple voltages and hot conditions. Failure of these capacitors is likely to cause problems with the operation of the the computer, so if I was reconditioning an old PSU, that's where I'd start.

[dalek]

Looks like the folks on a1k are already aware of the issue. One guy came up with the idea of replacing the whole IEC socket and heatshrink mess containing the line filter caps with an off the shelf line filter IEC socket (like this: http://au.element14.com/schaffner/fn...-3a/dp/1390927 - or higher rated if you want)



If I hadn't already ordered a replacement X2 cap that's the way I'd go for the A2000 Eltek.

[A4000Bear]

I'm very aware of those capacitors, having had them blow up in numerous electronic items over the years. They can also be found in those IEC mains sockets that contain filters.

The reason they fail is that the dielectric (insulator) in those capactors is made from paper. Over time they absorb moisture, causing leakage currents to flow resulting in localised heating in the capacitor. Once it gets bad enough....

These capacitors almost always are enclosed in transparent tan coloured cases. If you inspect one that hasn't blown up yet, you will see the casing is covered in tiny cracks. This is caused by the capacitor inside swelling up with the moisture. The cracks let in more moisture.....and you get the idea.

Modern X2 capacitors now have a plastic dielectric, mostly eliminating the problem. Its worth noting that these items are intended for interference suppression. The computer will work perfectly without them, and now that interference prone analog TV is long gone, the reason for them being there is now mostly redundant.

[Kepler]

I am reviving this thread as my RIFA exploded in my power supply but there is nothing to determine it's value other than the writing PME 271 M. There is another mains capacitor but it's not a RIFA (X2 40/100/21 .22 uF).
Can anyone confirm what the value of the exploded one should be (C4)?