Another set on the bench
 

I've got a Admiral Triple thrill chassis 301A-S that has developed a "snap, crackle, pop" in the sound and picture. The actual sound signal seems weak or has just been overwhelmed with noise. The picture is good with the exception of occasional flashes, snow and jumps that seem to be in sync with the noise from the speaker. Iv'e tested all the tubes, which test good, pulled all the video tubes one at a time and found that when I pull the first video IF the raster will stabilize but still have noise in the sound, I've pulled the HV tubes and still have the audio noise with no raster. Now....If i'm reading the schematic correctly this is a split sound receiver, the video and audio signals split out of the tuner, so my first thought, is that the trouble is in the front end, or could there be a problem in the LV circuit that could effect both sound and picture? I've cleaned the tuner barrel contacts with no change. Any thoughts or suggestions?


Thanks
Chris

....And here I thought this was going to be a weightlifting thread!

Seriously, I'd say unhook the tuner, or at least pull the RF & mixer/osc tubes, and see what happens. If that kills the noise in both audio & video, then try a SubstiTuner f you have one, or inject a signal from an Analyst, if available. 9 of 10 times in my experience, pops and disturbances in the pic and audio at the same time, are power supply or sweep/HV-related. In your case it sounds like you've eliminated those though.

Charles

I've pulled both tubes in the tuner and no change at all, I will say that when I turn the brightness all the way down it seems to get slightly worse. When you refer to power supply are you referring to HV? LV? or both?

My Admiral developed high voltage leakage due to dirt under the high voltaage rectifier socket. I bad to turn all room lights out to find it. It started as a corona and would arc down the doorknob cap slightly.
Cleaning the socket and capacitor remedied the problem.

When you turn the brightness down, the HV goes up (and so does the B+ somewhat), so that's a BIG clue that it's power supply-related; HV or LV. 9 of 10 times, it's HV, but an internally arcing 5U4 could certainly do it too. I'm not familiar with that Admiral chassis #, so if it has a metal CRT, check for dirt around any and all mounts of the CRT, and check that the anode clip is secure at the front edge of the tube. Also check the HV cage and under the 1B3 socket, etc., for arcing. Sniff for any ozone smell, as that's a corona leak. As Zenith26kc20 said, you can turn the lights out and look around for blue corona beams, but usually corona doesn't cause popping. Usually it's arcing/snapping which causes that. Another trick is to aggravate the problem for testing purposes, by putting the chassis in a humid place and see if it gets worse or more obvious where it's arcing. Maybe in the garage or basement early in the morning, next to an open window in wet weather, etc. Some people will focus a humidifier toward the chassis, but I don't like that idea so well.

Charles

Charles and Zenith26kc20,
I decided to take your advise and put it in the dark, didn't see anything visual so I decided to give the HV cage and components a good cleaning, it was somewhat dusty in there. I sprayed everything down with contact cleaner and let it dry over night. I just fired it up and...........there's no cracks or pops or flashes, everything's back to normal.

thanks for your advise, every time I post something here I seem to always walk away with a little more knowledge and understanding on how these old TV's work and how to repair them. Thanks again

Windex would probably have been a better choice for cleaning.

Many of the modern spray contact cleaners, even after drying, continue to attract dirt.

James.

For many cleaning jobs, I use plain old isopropyl alcohol (rubbing alcohol), which leaves no residue.

Cleaning is such a basic (and easy!) step that I included it in this article, "First Steps in Restoration."

http://antiqueradio.org/FirstStepsInRestoration.htm

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html