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View Full Version : Replacements for 'blowing' rice-paper capacitors on Osborne1



RizThomas
March 13th, 2012, 08:31 PM
Couple of weeks ago, I picked up an Osborne1 for $20 and today, I decided to refurbish (clean and lubricate) the floppy drives which were failing to read the CPM system disk. After spending some time, I was busy copying the system disk when suddenly a 'big' smoke came sizzling out of the P/s board. It turned out that I just experienced what Tezza was describing in his blog --- 'blowing' rice paper capacitors. I picked up some equivalent ceramic capacitors but because these are for RF filtering, I wonder what Capacitor type I should be really using as replacements. I replaced the 3 rice-paper caps on the PS board but I noticed that there are some also on the Monitor board. Maybe I should be shopping for the right types.

Can anyone suggest what would be the best replacement. Thanks

RizThomas

Chuck(G)
March 13th, 2012, 09:09 PM
Well, not "rice paper"per se, the Rifa units that appear to fail most often are epoxy-encapsulated metallized paper units. But any non-polar (or bipolar) capacitor with a class X1 or X2 safety rating will do the job. They can come in polyester, polypropylene, or (gasp) even epoxy-encapsulated metallized paper (Rifa/Evox is still made and distributed by Vishay).

RizThomas
March 13th, 2012, 10:10 PM
Thanks so much Chuck for the info. I used the term that was used by Tezza for describing these ones. Now that you have said, I looked at the capacitors and it truly shows the logo Rifa on it. :D
Now just to find who carries them here locally.

Chuck(G)
March 13th, 2012, 10:22 PM
I dunno; most capacitors come from the Far East anyway. Here are some Chinese sources (http://www.ebay.ca/sch/i.html?_nkw=class+%28x%2Cx1%2Cx2%2Cy1%2Cy2%29+capa citor&_sacat=0&_odkw=line+filter+capacitor&_osacat=0&_trksid=p3286.c0.m270.l1313).

glitch
March 14th, 2012, 04:21 AM
I generally use Sprague Orange Drop capacitors for all of my line noise filtering needs. Mostly because I've got a bin that has similar lead spacing to most of the smoke capsules I end up replacing. You can still buy them from quite a few sources.

"Don't be vague -- Ask for Sprague!"

Chuck(G)
March 14th, 2012, 09:32 AM
Are the orange drops Class X? There's a safety concern there--Class X and Y capacitors are supposed to fail in a way not to incinerate or electrocute the user--and be somewhat tolerant of spikes on the line. You can tell by the label of an "X" or "Y" in a rectangle or circle on the cap body.

pearce_jj
March 14th, 2012, 11:01 AM
Just to mention, when replacing RIFA's in a 5150 PSU recently I found that they had a different pitch to everything else available. Fortunately in that case IBM had provided two sets of mounting holes, the unused set of which matched up to products currently available (10mm in that case, iirc).

tezza
March 14th, 2012, 11:51 AM
Thanks so much Chuck for the info. I used the term that was used by Tezza for describing these ones. Now that you have said, I looked at the capacitors and it truly shows the logo Rifa on it. :D
Now just to find who carries them here locally.

Yes, sorry about that. I wrote that article not long after I started to dabble with hardware. I'm not sure where I got the term now..probably on some article I read at the time. Perhaps original ones were made from rice paper? Anyway chuck is right..a more accurate term is metallized paper caps.

I should revisit some of my old blogs and correct these things. I know a lot more about hardware now than I did then.

Tez

glitch
March 14th, 2012, 03:42 PM
Are the orange drops Class X? There's a safety concern there--Class X and Y capacitors are supposed to fail in a way not to incinerate or electrocute the user--and be somewhat tolerant of spikes on the line. You can tell by the label of an "X" or "Y" in a rectangle or circle on the cap body.

Hm, I don't know. I've got Mallory-made Orange Drops in front of me, and they don't. They're also 600 volt devices (I use them in repairing tube equipment), so I'm not sure if it's even a concern. I've got a pile of 0.015 uF @ 600 V Orange Drops that usually get used for PSU noise filter replacements, in both tube stuff (stops line pops in tube audio equipment) and vintage computers.

While I'm confident enough to continue using them in my own projects, do you think there's a legitimate enough concern about the Class X rating to warrant getting actual Class X marked caps for equipment repaired for others?

Chuck(G)
March 14th, 2012, 04:36 PM
This is one of those things between you and what you see in the mirror when you're shaving.

If I were working with something I intended to sell later, or were to have other people use, I'd go for the rated caps. A class X cap is supposed to not catch fire when it goes and is supposed to be able to tolerate moderate line surges. A class Y is like a class X, but in addition, it's supposed to fail open (Class Y caps generally are used between one side of the line and chassis, so you don't want them to fail and give you a "hot" chassis).

In any case, those "orange drop" Spragues should have an AC rating on them, not the usual polarized stuff with a DC rating.

RizThomas
March 14th, 2012, 10:15 PM
Original post by pearce_jj
Just to mention, when replacing RIFA's in a 5150 PSU recently I found that they had a different pitch to everything else available. Fortunately in that case IBM had provided two sets of mounting holes, the unused set of which matched up to products currently available (10mm in that case, iirc).

I found that Osborne 1 has the same extra mounting holes.

Tezza: Actually I have been reading your article before I had this Osborne1. So when the cap started smoking, the first thought for me was to go to your site and read that part about the capacitor. Hey, if you look closely inside, there are metalized paper inside...which may have been the source of that term.
....I enjoyed your article.

For everyone's info, we have another resurrected retro Osborne1. After I lubricated the floppy drive's "r/w head mechanism", I was able to copy the original Osborne disks. It took me a few tries...I guess the diskettes needed a few turns to really loosen up..which made the reading and writing become successful.

I replaced the capacitors with new 600v rating for the 0.1uf and the 2 - .01uf were at 400v. I had to use these since they are the only on stock at my local electronic shop.

tezza
March 14th, 2012, 11:28 PM
Good to see more Ozzies live again! (:

Tez