Why you should replace Capacitors.

[Eric H]

Found this post over at A.R.F. and thought it was a good lesson in why Caps need replaced, particularly Electrolytics.

http://www.antiqueradios.com/forums/...p?f=2&t=209675

The first picture shows the can that exploded, the second shows the hole the can punched in the ceiling!

If you happened to be in the path of such a projectile it could do serious damage to your body!

[maxhifi]

Wow! Maybe also an argument for installing fuses in old equipment, and keeping covers installed!

[Jeffhs]

It could have been much worse than that. In one of the VK B&W TV forums, there is a post by VK member radiotron (Johnny the Raster Master) that tells first hand what can and often does happen when a vintage or antique radio or TV is plugged in without changing at least the filter caps, most if not all of which, in vintage sets, are either defective (often shorted, losing value, or both) or are on the way to failure. I'd almost count on the former in '50s and earlier sets; in fact, filter caps that are bad enough to cause AC hum should be replaced ASAP, as they are probably going to short at any time.

Shorted caps, as we know, will overload the power transformer (in sets so equipped) and cause a fire if, for any reason, the set's own fuse or the house fuse does not blow (for example, if the short is a high-resistance one, though most overloads caused by shorted filter capacitors are low-resistance shorts and will, of course, pop the fuse, if present, or cause major damage if there is no fuse , in a hurry). I am reminded of an article I read in, IIRC, Reader's Digest some years ago, in which a house fire in Cincinnati, Ohio in the early '60s was caused by a thoughtless homeowner who put a copper penny behind a fuse that kept blowing in his fuse box, rather than unplugging the defective appliance or other device that was overloading the line. A major fire resulted; the house sustained very severe and costly damage that could have been prevented had the fuse box been replaced with a breaker panel than cannot be bypassed.

[maxhifi]

Originally Posted by Jeffhs

A major fire resulted; the house sustained very severe and costly damage that could have been prevented had the fuse box been replaced with a breaker panel than cannot be bypassed.

Fair enough, but I have seen people put 30A breakers on #14 wire going to a garage, so they can use power tools without tripping the regular 15A breaker.

Honestly, if I had a fuse panel, there's no way I would replace it with a breaker panel unless it was either worn out, or my insurance company forced me to. Fuses clear a fault faster and more reliably than breakers do, and are every bit as safe if used properly.

[CoogarXR]

I had a smaller cap (1000uf 16v, I believe) shoot off and hit me in the lip at close range. That hurt like a beeotch and left me with a fat bleeding lip.

I was careless on an LCD tv though, it was my fault. I left the power supply screws out, and I was probing around and pushed it off its mounts. It fell down and grounded out against the back of the panel. I heard the shotgun blast and felt the punch in the face. Yeeouch...

[snelson903]

wow that must have been boiling inside before it exploded ,iv only had one cap explode near me and it looked like confettie raining down, small paper fragments all over, at first i dint see what happened.

[Penthode]

I do not know what the fuss is about always changing the filter caps?

Sure, they should be replaced if you are not going to reform them. Certainly they will explode if the equipment is powered up after sitting idle for thirty or forty years.

I have had no problem with most can electrolytics. I simply reform the dielectric. It is important to ensure the dielectric reforms; eg the leakage current remains low. After ensuring the dielectric reforms okay, monitor the capacitors while the equipment is powered: I'll bench test for at least a couple of weeks. If the capacitors get even slightly warm, they must be replaced. If they remain cool, they'll probaby last another 50 or 60 years.

I have a number of old radios and TV's with most or all original electrolytics and they work fine.

[DavGoodlin]

By dielectric reforming, are you referring to a re-establishment of the rated capacitiance in a "partially open" electrolytic?

I was originally thinking this meant to restore the integrity of the dielectric if it was leaky.

I have a box full of multi-section electrolytics for cosmetic restorations and decided to test them last week. I found that in almost all of them, 1 or 2 sections had excessive leakage breaking down at a much lower than rated voltage. A few were open but a majority tested at rated capacitance.

[Jeffhs]

Originally Posted by Penthode

I do not know what the fuss is about always changing the filter caps?

Sure, they should be replaced if you are not going to reform them. Certainly they will explode if the equipment is powered up after sitting idle for thirty or forty years.

I have had no problem with most can electrolytics. I simply reform the dielectric. It is important to ensure the dielectric reforms; eg the leakage current remains low. After ensuring the dielectric reforms okay, monitor the capacitors while the equipment is powered: I'll bench test for at least a couple of weeks. If the capacitors get even slightly warm, they must be replaced. If they remain cool, they'll probaby last another 50 or 60 years.

I have a number of old radios and TV's with most or all original electrolytics and they work fine.

I have a Zenith H511Y radio that I won in an eBay auction in 2002. Made the mistake of plugging it in as soon as I removed it from the shipping box. The radio worked, but the pilot light (#47) burned out with a bright white flash as soon as I turned the set on. I think this was because the 3-section filter capacitor had become deformed after decades of disuse; when I replaced the pilot light, the new one didn't burn out so the cap must have reformed -- or else the old bulb was ready to burn out anyway, after 40+ years.

Don't know for certain, but I think this radio may have been sitting in its former owner's garage, basement or attic for years or decades, unused, before he/she listed it on eBay, which would account for the deforming of the filter capacitor. Haven't yet checked the cap for temperature, but the radio isn't humming (at least not loud enough to hear), so the filter must still be OK.

My next project is finding the cause of a hum in my Zenith C-845. I'd check the filter in that radio to see if it's warm, indicating a defective capacitor (it may well be defective and on its way to shorting, since this radio is 52 years old), but I don't have a cheater cord that will fit the set's interlock plug (the pins seem thicker and slightly wider spaced than most standard interlocks) and, of course, I don't want to defeat the radio's own safety interlock system if I can possibly avoid it. Better to be safe than sorry.

[Penthode]

Originally Posted by DavGoodlin

By dielectric reforming, are you referring to a re-establishment of the rated capacitiance in a "partially open" electrolytic?

I was originally thinking this meant to restore the integrity of the dielectric if it was leaky.

I was actually referring to the leakage problem. If the capacitor has been sitting for many years unused, then the dielectric leakage will increase. Plugging in a set which has been unused for decades is asking for trouble.

I use a Sprague TO6 Capacitor Checker to reform the dielectric. The TO6 has a hi voltage power supply with a milliammeter. I will find that if I apply a voltage across the capacitor and limit the initial leakage to no more than 6 mA, over time, the leakage will drop. I will reach full rated voltage within an hour or two and the leakage will drop below 100 microamps. If the leakage remains low, then the capacitor should be okay so long as the capacitance measurement is correct.

After this process, I have had a capacitor open circuit but never short. I have had a set where someone plugged in the set before I have had a chance to reform the capacitors. In this case I have found capacitors only rarely irrepairable. The old Sprague and Mallory aluminum can capacitors have great healing ability.

I am amused by others who immediately replace the electrolytics without first checking them. I wonder whether the replacement being stuffed into the old cans will last as long as the originals!