TV went Big Bang.

[Bill Cahill]

Hi.Last year I fully rebuilt my 1949 RCA Victor 9T270 tv. I brought it up to 110v ac on variac, had B+, and a low audio hum, but, nothing else. After checking thoroughly, I found I had shorted micas in horiz. osc. I finally replaced them and got circiut back together. Tried it Sat. At 40v on variac, I was still bringing it up, I noticed I was only getting about 1v of b+, suddenly, the tv made a loud bang. No smoke, no fire. I quickly shut it down, and changed my meter settings to resistance. Discovered that somewhere in themiddle of the circuit, I have a 1K short. I have so far disconnected several circuts, including the one I was working on, horiz. out., and damper, and, short is still there. Can anyone help me? Thanks.....

[jpdylon]

Maybe a filter cap is shorted? That would explain the audio hum. It could also be the cap across the AC line. SOmetimes they short and blow up, but don't leave any smoke or fire.

The best thing to do with these old sets is to bring them up after re-capping and not before. This way you don't potentially cause any unnecessary damage from a shorted cap.

[Bill Cahill]

No, as I said, all filters are new. Audio hum is just a variable hum showing amp was working. I don't have line caps in. All paper is replaced...

[Chad Hauris]

Have you located the burned component yet? This is a good time for the series light bulb in power line (60-100 watts). First remove the rectifier tube and see if the bulb glows bright...if it does, there is a short in the filament system or the power transformer itself.
Just keep removing or adding loads to the power supply circuits and note how the bulb glows to find the short,
Also it is a good idea to always install a fuse holder in power line, you can tuck an inline one under the chassis. 3 to 5 amp fuse. For some stupid reason there often is not a fuse included in these early sets and installing one will save your power transformer in case of a short.

[kx250rider]

I had an RCA 8T241 do that a couple years ago, but my B+ was fine and continued to rise normally and the set worked great. So your B+ not coming up means my POP! and your POP! are probably not the same. It was a very sharp POP! and a wisp of smoke, and a bright flash from under the chassis. I never figured out what did it, and it did it again several startups later! No burnt components, no cockroaches (seen them cause POP!-FLASH before)...

So take a very close look, not only for exploded caps, but cracked apart resistors, or even a component lead that arced to the chassis or another component lead. That happens to the best of us when recapping a set. It will cause a flash-pop, and could then be a short if the lead welds itsself to whatever it touched.

Charles

[pallophotophone]

Hi !
I'd check for a shorted MULLER resistor in the b plus circuit. (Does this set have one ?) I'll bet it does. It is usually rivited to the chassis and has multiple taps.

I've seem many of these go to ground without warning when the internal fiber insulator goes south.

Good Luck !

Bob

[Bill Cahill]

Thanks, guys. haven't been on it in the last week.Will be getting back on it soon. thanks. i think I will check that back panel resistor. Never seen 'em fail on this late a set, but, there's always a first time. Nothing is impossible. Thanks for the tip. I'll let you know what I find.


"Money talks mine says adios."

[radio63]

Did you check the new filter caps before you installed them? There is the remote possibility that one of the new filters you installed is defective. May be worth checking out the new caps just to be sure. There is always a possibility this could be a problem.