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Old 03-24-2003, 10:50 PM
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Joel Cairo Joel Cairo is offline
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Help needed for the newbie...

Well, I got brave and powered up the CTC-5 tonight, on a reduced-voltage basis for a couple of hours, then held my breath, plugged her in and turned her on... which I now know to be the moment of truth.

It wasn't even on long enough to warm up when I heard an audible *POP* after a couple of seconds that came from the rear of the set. Quickly turned it off and unplugged it. No smell of anything frying or even smoldering, which I took to be at least a **decent** sign.

So without being able to get inside and troubleshoot this evening, what did I most likely hear? A small cap going out? A wild high voltage charge arcing?

Has this happened to anyone else on the first power-up? Did I screw something up? (hope not!!) What should I be looking for when I can get the back off? The key work is **look**, by the way... lord knows I'm not certain that I want to touch anything at this point!!

I realize this is a far from scientific set of questions, but I think I just need a little reassurance that these things happen from time to time...

Thanks, all...

-Kevin
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Old 03-25-2003, 12:18 AM
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High voltage arcs I've had made more of a "snap" sound instead of a pop. A snap and no smoke could be high voltage. Could also be a short in the neck of the CRT. I have a 21FBP22 in an RCA that arcs in the neck occasionally.

A cap blowing would leave behind a small mess... depending on the size of the cap. The degree of smoke and smell would also vary with the cap size. Might need to look under the chassis for evidence of a blown cap.

When firing up a set, whether for the first time or after replacing parts, I always felt it was best to be watching from the back so that if something craps out, it is likely you will see or hear what it was, or at least what area it was in. You can always watch the CRT from the back with a mirror in front of it while watching the chassis.

I've had caps blow a few times... usually small pops. Had a small electrolytic give way once. That one was a real attention getter! It left a very big mess. Other failures I've experienced include snaps, sizzles, fizzles, and a little smoke. Also had a cool light show from a wire that grounded out on the chassis due to worn insulation.
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Old 03-25-2003, 12:52 AM
Rob Rob is offline
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Exclamation Careful operating on reduced voltage!

It is not a good idea to operate tube type television receivers on reduced voltage between approximately over 50 volts and less than 100 volts. This is more potentially damaging in the case of vintage color receivers. Once sufficient filament power starts the tubes to conduct but the B+ is insufficient to provide proper oeration, the horizontal output tube can be placed conducting excessive current through the flyback without the H. oscillator operating. This excess current can burn out the flyback. In the case of vintage color receivers, the flyback is a critical and often hard to find replacement part.

If one wishes to form electrolytics in a vintage tube TV at reduced line voltage from a variac, best to pull the horizontal output tube during the process.

Rob
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Old 03-25-2003, 01:24 AM
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Joel Cairo Joel Cairo is offline
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Thanks, guys...

Charlie: About the CRT arcing-- is this something that just may happen from time to time, and is-- well..., **OK** to allow it to happen?

Rob: Message received about the cap re-forming... I thought I read in some previous forum posts that this was a common way to wake up old receivers, though... hmm-- obviously, I was wrong.

Now, when I get the back off-- if the snap I heard was from an arc, I should look for evidence of a burn, I would suppose... though I may not find one even if that is the problem, I'm guessing.

Will a failed electrolytic can be obvious? (leaky or scorched, etc?) Obviously a smaller blown cap will be visibly blown or deformed, but I wasn't sure about the can.

Although I was trying to err on the side of being conservative, did I perhaps call a halt to the experiment too soon? My biggest concern upon hearing the "pop" was to avoid blowing out something larger and harder to replace... Obviously, the eventual troubleshooting process will call for powering it back up, but I'm rather leery of doing that at this point. Would you recommend a visual inspection of the inside, first?

Just curious-- since I'm learning at this point, I don't mind taking some time with this set-- and I suspect a lot of the hard work has already been done... I just don't want to undo those previous restoration efforts!!

Thanks agin for the responses, folks!

-Kevin
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Old 03-25-2003, 08:15 AM
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The arcing in my CRT neck is not OK. For now, I can't do anything about it. I do not watch this set, and it has been a few months since I powered it up last. If I am not mistaken, my arcing problem can possibly be corrected by re-juving the CRT.

Depending on where your arc is coming from, you might not find a burn. It would be one of those things where you got to fire it back up and watch the insides. Reduce the ligthting in the room just a little.
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Old 03-26-2003, 01:30 AM
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i have heard big lytics make popping noises just before they short.
did you change the big cans?
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Old 03-26-2003, 02:49 AM
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Joel Cairo Joel Cairo is offline
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No, I didn't-- I tried it straight from the prior owner's re-build... I did notice that he'd recapped a lot of it, as there are Sprague Orange Drops in there, but I didn't check closely enough to see if the cap can was original.

Frankly, a popping cap can was the third thing on my list of possibilities (a tube going out was fourth)... I know from hanging around Steve Hoffman's audio forum that a popping can is a symptom that many people find when they're attempting to rebuild tube amps, and I've run across a couple of stories from folks that had them go totally bad... the central theme was that they made a big mess when they finally gave up the ghost. And of course, it can screw other things up, too.

That's why I'm pretty hesitant to hook the set back up to the juice until I can eyeball the insides... if it's an obvious problem, I'd like to eliminate it, lest I get impatient, do the wrong thing and end up damaging something that's a lot harder to replace. Which I understand is a possibility.

Wish I had your expertise, folks-- but I guess you all had to come by it the hard way-- just like I am. It's just that the first time is a bit intimidating, after being conditioned for years to call the TV repairman when something went wrong. (You know-- because he's a **professional**, after all!!)

Who knew that one day I'd be (gingerly) trying this myself!!

-Kevin
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Old 03-26-2003, 08:50 AM
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ChuckA ChuckA is offline
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Quote:
Originally posted by Joel Cairo
... the central theme was that they made a big mess when they finally gave up the ghost.

Not only can they make a big mess, but can be downright dangerous. I was resoring a Scott Philharmonic radio and replaced the can type electrolytics on the power supply chassis. As I was eyeballing my work I heard a slight sizzling sound coming from the PS chassis. Just as I was going to lean over the chassis one of the cans exploded, the metal can shot up 4 ft to the ceiling and embedded itself 3 inches into the drywall! Also I was cleaning tar and paper fuzz off the walls and the chassis for a week and it broke two of the output tubes.


Chuck
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Old 03-26-2003, 07:25 PM
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kc8adu kc8adu is offline
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i got to clean up the aftermath of a big cap that went bang.
it was in a imsai 8080.
i and a fellow vintage computer collecter got 2 imsai 8080's at an estate sale.
told him to bring his over to the shop so i could reform the caps.
his son unaware of the danger took off the cover and plugged it in.
5 minutes later it exploded.
missed the kids face by a few inches.
at least all it took to fix it was some new caps.
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