Sider burning odor

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Sider burning odor

Hello, I see there have been a few posts over the years about the Sider hard drive.  My Sider still works (10 MB), but today it started emitting an odor like burning, reminiscent of the smell when the Apple ][ power supply blew up.  I already recovered all the data to the Floppy Emu a couple months back, so that is not an issue.  What the Sider was doing before the odor came was partitioning and reformatting which takes a bit of time and I suppose stresses it a bit more than usual.  It was still working fine, but I quickly shut it down since I guess it is about to blow.  So I wondered if anyone has a suggestion for what to do next.  I took off the cover and I see the power supply does have these electrolytic caps which I gather are often the culprit.  Thanks for any thoughts.

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Check for Rifa Caps!

It could be the X2 capacitors. They're used for noise suppression. They're often RIFA branded mica acapcitors and look like a translucent yellow box.

(Google "Rifa cap" for an image)

These are notorious for blowing and making a bad smell. Replace them with a modern X2 cap of the same value capacitance and same or higher voltage rating. Doesn't need to be a Mica cap. I use Metallised Polypropylene ones as replacements.

 

Cheers!

 

Chesh.

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Those caps are almost

Those caps are almost certainly not mica. I don't think I have ever  seen a mica cap used on the mains. They are most likely metalized paper caps. Which is what the theory of them failing is. The cap swells, the case cracks, and moisture now makes its way into the paper dilectric causing havoc. Mica caps on the other hand don't really absorb moisture. Infact, in old tube radios adjustable capacitors that used mica insulation were open air and not sealed. 

 

 Regardless, if you are ever replacing a capacitor that touches the mains, always use a properly rated capacitor. Most capacitors are not rated at all for AC.  The caps meant for this purpose will have an AC rating and also carry a designator like X2, Y2, or even a combination of both. These caps are almost always film caps. 

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confirmed

Thank you for the notes, yes there is a cap just as you describe, with brown stuff all over it and nearby surfaces.  I've attached a photo.  There is another component with some sort of discoloration, if you have a moment to look and see what you think I would be interested.  Thanks again!

 

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lacquer

I could be wrong but isn't that just some kind of protective lacquer on that "8521.." thing?

The RIFA should of course be replaced. I can see 3 of them in your photo.

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I agree that just looks like

I agree that just looks like laquer on a transformer or something. And I also agree that there are probably 3 "rifa" caps in that picture that should be replaced with modern film caps with the proper ratings.

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Conclusion

The three x2 film capacitors are replaced (no other components disturbed) and the Sider is working with no sign of trouble.  If anyone else needs to do this, one comment is I found it hard to untether the power supply without breaking the feedthrough grommet.  An alternative would be to remove the board without untethering.  Connections to the board come off easily.

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