if an electrolytic cap was in backwards?

[jbivy]

So im slowly recapping a motorola tv, my soldering isnt great, so its slow going. A few caps were obviously replaced in the past and I found one, a yellow plastic .005-600 that was installed backwards. It was hooked to a 6au6 tube.

After getting this and checking the tubes on this and finding two dead ones, replacing them, i tried powering it on. The tubes lit up and i got the filament in the back of the crt was going. But no picture. So then i started recapping.

Could this replaced and backwards cap have been a major problem in why this tv ended up being retired from use?

again, sorry for the newby question. Just i think this shoddy repair could have been the culprit for this tv's demise.

[bgadow]

A .005 wouldn't be an electrolytic, at least not under normal circumstances. (I'm not sure you could ever buy them in such a small value?) Some "paper" caps were marked as polarized but it wasn't anything critical, you couldn't really hurt anything by installing them backwards. Now, a true electrolytic installed backwards, yes, that can cause real problems. I've done that more than once!

[jbivy]

oh, well it had the bar on one end meaning it should face away from the tube socket where it was hooked up. The replacement was facing in.

*shrugs*

Perhaps i was just hoping that they installed this backwards, blew a few things and thats why the tv was mothballed.

[bandersen]

I believe the bar indicated the end connected to the outer foil. It might have made a small difference to have that end grounded in some circuits. New caps don't seems to have an end marked anymore.

[radiotvnut]

Like what everyone else said, no problem here. The black band on some older paper caps identifies the outside foil connections and some caps even say "outer foil" by the band. In some circuits, it may make a slight difference in performance if the cap is wired backwards; but, there won't be any chance of it blowing up or frying other components.

An electrolytic cap, usually found in values of 1 uf and above, are a different story. Unless you are dealing with a non-polarized electrolytic cap, you will need to observe correct polarity. Standard polarized electrolytic caps have some type of indication as to the negative lead (usually an arrow with a "-" sign inside the arrow). If you install an electrolytic cap backwards, it can violently explode, fry other parts, and/or cause severe performance issues. In vintage electronic work, the most common place to find non-ploarized electrolytic caps is in the speaker crossover network in stereo's, phonograph's, etc.

[Username1]

Brandersen is right, the marked end is the outside foil end. It was thought that that side should be the grounded side if it were going to ground, and in that way keep noise down. But if you unwind one, you find the outside foil is only exposed to any outside potential noise for just the first 1/2 inch of the winding. Most likely your new cap has no outside foil marking. Radiotvnut is also right, in older sets electrolytics tend to be phisically larger than all other caps you see, so Identifying them in older tube sets is a little easier, and there is a polarity marking in them, not just a stripe around one end. If you have a schematic for the set you are working on, they are marked as polarized on the diagram.

[Robert Grant]

I accidentally back-charged an electrolytic a few years ago (I wired a 90V B battery in reverse on a 3-way portable tube radio).

A soft, slow explosion, a puff of smoke, and a trip back into the chassis to replace an electrolytic.

This was when I found the answer to my old question of why so many electrolytics had a cross in the top. the top is scored so that it fails if the pressure gets too high, allowing a relatively soft "pop" instead of exploding like a firecracker, and it worked.

[Reece]

Yes, and sometimes the cross lets them "ooze" their little guts out when they are getting old and tired and overstressed and they are getting marginal.