No, that’s incorrect. If the set is isolated from earth ground the only current flow with be from the HV+ to a neutral spot on the set until the voltages are equal, which won’t take long. You’ll still have a huge charge in place, with no place for it to go, except possibly through you.
I’m not following. What are the two points with a charge between them?
I can tell you from personal experience that every single set I’ve worked on was unplugged, i.e. disconnected from earth ground, and after each had the technique I described (shorting from the output of the flyback to the chassis ground), there was no danger in working with the flyback. This isn’t just my experience; it’s standard operating procedure for fixing a flyback.
So I guess I’m not sure what you’re saying. Where is the dangerous voltage after the flyback/picture tube have been discharged?
The reason there is high voltage present after you’ve unpluged the set is because there are HV capacitors which can store a considerable charge. If the point you choose to connect your discharge jumper to isn’t connected to the opposite plate of the cap, you’re not discharging it. My point was to warn those unfamiliar with this sort of thing that there are pitfalls.
Well, not quite. I’ve read everything Bill H. has said, and he’s 100% correct.
Like Bill, I have also discharged many TVs in my days using the screwdriver technique. And it is not necessary for the TV to be connected to earth ground. In fact, whenever I discharge the high voltage, I make sure it’s not plugged in to 120 VAC…
When you use the screwdriver technique, you are simply “self-shorting” the stored high voltage. It is no different than discharging a capacitor by connecting its two leads together. Note that you do not need to connect the leads to earth ground; the current simply flows until the voltage goes to zero.
Yes, IF you connect the other end to the right spot, as I said above.
Agreed. And that’s why it’s best to do this under low-light conditions. (You know you’ve discharged the HV when you see the arc.)
The other problem when novices attempt this sort of thing is “Gee, that round metal thing looks like a good ground”, and there goes the horizontal output transistor. I wasn’t so much saying Bill H. was wrong as trying to deter someone without experience from causing a minor (or even major) electrical catastrophe.
Old TV repairman here.
Hey guys" whatever it is that is connected directly behind the vacuum tube" sounds like the yoke to me.
Its been years since I’ve had the back off a set so I’m not familiar with todays alignment procedures.I bow to your explanations.
But— I’ve been zapped by 25K before. The worst that has happened is bloody scratches trying to get my hand out of there.
No, television HV isn’t necessarily instantly fatal. I just think no one wants to be the one responsible for “Hey, did you hear about poor MGibson? Yeah, his TV got him.”
In any case, your point about the yoke is a good one. Not much you can do about that either, unless the noise is being caused by a few loose windings, in which case painting with a bit of electrical varnish might silence it (with the same caveats about unplugging and discharging). As far as adjustments, for the most part, gone are the days of the 2-, 4- and 6-pole magnets to be adjusted. It’s almost all electronic, being adjusted through an onscreen service menu. There’s hardly even any pots on the boards in these things anymore.
I’ve seen a guy zapped by “only” 600 volts and he was seriously hurt. Not by the 600 V but because it made him jump back and he hit the back of his head pretty badly. Know what you are doing before you go in there. Fools rush where expert repairmen tread carefully.
**
I appreciate everybody’s concerns about my safety. I only know a little bit about electronics but I did know that certain parts of the tv would hold a charge long after I unplugged it. I just thought I’d check to see if there was something I could do about it. As I said I only know a little bit about electronics but I do know when I should and shouldn’t attempt something.
If it makes any difference the buzzing sound doesn’t start until the television has been on for a few minutes.
Marc
.
“Percussive maintenance” is always worth a try.
Wait till the set starts to buzz, then whack it with the side of your fist.
Ah yes, the old “smack it” solution. I had a friend (who just passed away a couple of weeks ago at a young age, big bummer) who was a framer. His big joke in life was that whenever you’d ask him for any tool at all, like say a screwdriver, he’d hand you his big-ass framing hammer and say “here, use my screwdriver”.
Unfortunately, I don’t think that solution will work here though. Whatever is making that sound (90% chance flyback transformer, 8% chance yolk, 2% chance something else) is making it because some pieces of metal (either metal plates in a transformer or strands of wire) which were once held together tightly by resin or epoxy have now come loose. And as electricity goes through them to intentially create an alternating magnetic field, the magnetic field causes them to vibrate.
A good smack will often cure a bad solder joint (temporarily at least), and a few other ills, but this one is unlikely to be a good candidate for that treatment.
justwannano wrote
After reading the OP again, it sounds like you could be right. I guess I just assumed the location. MGibson, are you familiar with physically what the yoke and the flyback look like and are located? Perhaps you can isolate the buzz by listening carefully to where it’s coming from.
If it is the yoke, often you can take it off and spray the entire surface of it with motor armature spray sealant. Painting a section with varnish as Q.E.D. pointed out will also work, but to do that you really need to know where it’s loose. I prefer spraying the whole thing, as you won’t be trying several times hoping you hit it. If you spray the whole thing good, and it isn’t fixed, then you know you did everything you could, and can accept that a new yoke is in order.
However, toying with the yoke at all will likely require reconvergence when you’re done. And as Q.E.D. pointed out earlier, it’s often difficult to do nowadays. On my set at home, I had to go to a lot of trouble just to find the special magic key strokes you had to do on the remote control just to get to the on-screen adjustments. Once you’re there, you can play and maybe converge it reasonably by trial and error, but even if you don’t you can still take it into a shop and have them converge it for you. There’s not a lot of physical danger in trying.
Which goes to show that even if you don’t die from a 25K hit you can count on it being an unpleasant experience.
Also…while this is a major hijack…I thought it was amperage that killed people and not voltage. IIRC a Van de Graaff generator puts out tens of thousands of volts but the amperage is so weak it doesn’t hurt you (much) to touch it. As such is a shock from a capacitor in a TV more likely to be painful than lethal? I guess I’m asking that no doubt the potential for a lethal shock exists and as such one should certainly be careful but how likely is being killed from one (assuming you don’t have a foot in a puddle and grabbing a metal frame with one hand while you reach in and grab the capacitor with the other)?
My 2 cents
To repeat the question someone else asked, where is the buzzing coming from? The speakers, or the back of the set?
If the noise is coming from the flyback it will likely be a high pitched whistle not a low frequency buzzing.
Does the buzzing occur when there is a lot of bright white in the picture, such as text or graphics? Does it occur on all of the stations that you watch or just one? If just one, the station may be overmodulating the video portion of their signal and the video synch pulse may be bleeding over into your audio circuitry. If it occurs on all of the stations it’s probably time for a new TV.
-KOh this is an easy one!
Done this plenty of times.
Turn your tv off and leave it for a few days I assume you don’t know enough to discharge the tube safely)
Open the back and undo the retainers for the main circuit board, it will slide out a few inches, you probably will not need to disconnect any of the wiring to gain enough acces.
Get yourself some superglue, the runny sort rather than the slightly thicker stuff.
Carefully tip it between the laminations of your flyback transformer.
Done.
We in the UK call this device the Line Output Poer Tranformer(LOPT) BTW.
**
I’m not really at all familiar with the innards of a television. 
After all I did describe the sound as coming from “whatever it is that is attached directly behind the vacuum tube.” I did isolate the buzz by listening. I knew it was coming from somewhere behind the tube and confirmed it after I took the back off and then turned on the television.
**
I think I’ll just live with the buzzing for now and perhaps get a new one next year. At the very least I won’t attempt any repairs until I’ve got the cash to purchase a new one with.
Marc
**
No sound comes from the speakers.
**
It is a high pitched buzzing sound. If the television has been off for a while it doesn’t buzz when I turn it on. It doesn’t start buzzing until the television has been on for a while.
**
It occurs on all stations and doesn’t really change depending on what’s on the screen.
Marc
Thank you all for trying to help me with my little television problem. One of these days I might bake y’all some cookies.
Marc