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TV giving off high pitch hum. Answered

Well I recently inherited a old TV it is an SDTV and it is about seven years old. So I decided to test it with my computers osciloscope and using the microphone on it i turned the osciloscope on and there was one constant signal that went up and down about 3 or four KHZ every second or two. But when I muted the TV their was the normal background noise at about 1-7 KHZ but one signal that I found is about 16-17 KHZ and 5.94 DB, and when I turn the TV off it stops and that 16-17 signal disapers. So how do I get rid of this annoying high pitch noise?


. Unless you know how to work around high voltage (the CRT stores a BIG charge, even with the power off and unplugged from the wall, and the FBT is connected to the CRT), I'd learn to live with the squeal.

yep CRT works like a capacitor had one laying around, turn on my tesla coil. About half an hour later I was reorganizing stuff and it gave me a nasty bite

yep. you need to unplug for a few hours atleast and discharge the high voltage manually the high voltage is made by the flyback transformer - usually it looks like black device in the corner of the circuit board and there are wires exiting from the top of it. one goes to a cap on the side of the CRT. this is the main danger. it can have 30+ KV on it. other 1 or 2 go to the small circuit board on the back of the CRT. they are less dangerous but may still have few KV. dont get near them the board itself contains capacitors that may be charged with up to 400 V. this is less dangerous than the high voltage as it cannot flash to you if you just get near it. dont touch the circuit board or its components and youll be ok there is 'ible how to discharge a CRT TV by Plasmana. note - in the instructable there is something with screwdriver sticked in the ground. dont do it. instead connect the end of the wire to the uncoaed wire with some springs thats on the back of the CRT

. The idea is to have a fairly high-resistance path to Earth. A CRT stores enough energy to melt a wire if discharged quickly. I use a 1-10 Megohm resistor.

hmm yep there is something in it however just a TV laying on the ground is like isolated from it with resistance well above 10 M ohm. when you stick it it does not discharge anything just places the entire TV at 30 KV against the ground creating more danger you do need some path for it to discharge the resistor is the best option. where do you get high power high resistance resistor ?

> however just a TV laying ... . I have no idea what you mean. . . Don't need high-power; 1W works for me. Wattage is not the problem, it's the physical size - HV can arc across a ¼W resistor.

I have no idea what you guys mean? Can you explain this in lay-mans terms for me? Thanks!

if you just short the high voltage with wire the discharge may be powerfull enough to damage that wire or the TV so you need to slow down the discharge by adding resistance you can use a resistor for that if the resistor is too small in its size the high voltage may flash from one wire to another bypassing the resistor completely an option then is to connect a series of equal 1/4 w resistors that together make enough length to avoid the flash

if the resistor is too small in its size the high voltage may flash from one wire to another bypassing the resistor completely

And if the amperage is high enough with it seeing a short, it may just pop like an unenclosed fuse.

If you are this unfamiliar with electrical and electronic discussions, don't open up the TV right away. Get yourself a couple of good basic books on electricity (electrical circuits) and electronics, play around with some simple DC circuits (resistors, capacitors, LEDs), then come back to your TV set in a couple of weeks.

The internals of a tube-type TV use kilovolts to drive the electron gun, and millifarad capacitors which can store a lot of charge (yes, I know that's redundant). If you touch the wrong two contacts with opposite hands, you can kill yourself. I'm not being figurative: 500 mA (the current through a 60 watt light bulb) or 50 joules of energy (current × voltage) across your heart is enough to put it into ventricular fibrillation.

The people posting here are familiar with the basics of HV safety, and are giving you recommendations based on that experience. If you don't understand the terminology, you are very likely to make a mistake.

Yeah im gonna get shocked then, because I am a intermediate newbie with circuit boards and I dont want to get shocked.

That would be my guess too, as the operating range in kHz is around what he is experiencing. The electron gun used inside the CRT can cause this too, on occasion.

I've found it more commonly to do with a bum power supply, however the flyback may be making the noise because of it. I have one TV that makes a tone at around 20khz, it was much louder in the house with funny electrics, which is probably why we used to get so much scrapped electronics. It varied though, if it went loud it put you on your knees in pain, my brother used it for a good while since he can't hear the tone anyway. As far as I know there's not an easy fix but you could possibly try some shielding on cables or the like, probably too dangerous near the flyback though.

Mine does this too and it doesn't help that I have tinnitus at the same time!

Transistors whine, and there's not to much you can do about it, save the TV for a couple more years and you'll lose that part of your hearing ...

Wait do you mean that part of my hearin is going to go deaf from watching this TV?!!!?

it sure is not good to your health my tip : when you notice something like high pitch noise or flickering or unfocused screen fix the problem. never try to 'get along' with it

So long as the db level is not to high there is no harm done, it only takes a few db whine at 15 kHz in a quite room to drive people nuts, and it's common for transistors to whine at the CRT scan frequencies, and even if you go as far as full out replacement this may not solve the problem (( you could pot the entire unit in epoxy but this may very well over heat it )) it is some thing that happens but I have yet to see a power transistor output an audio signal that will cause hearing damage, they are not really built to be that efficient as a speaker... Now the unfocused screen that could be a real issue because if someone adjusts the high voltage potential on the CRT it will emit higher levels of X-rays, and it will lose focus, but this is not what the problem is ((( Should this ever be a problem there is instructions printed inside every TV on how to set the voltage to a safe level and most new TV's have built in protection and they shut it down if some thing goes wrong to protect you... ))

you may use an unfocussed monitor. there is no proven damage from using it but i am sure there is same goes for the noise from the TV. the fact you noticed it and it annoys you is nature's way to tell you its harmfull in long exposure the fact you get used to it after a while means that damage is done it does not need to be powerfull enough to cause 'standard' damage. very faint thing can make damage when it is there for long time

Adjusting the high voltage potental affecting the screen focus is proven to be hazardous, X-rays are known to be hazardous, even in low doses... ((( There is a large warning inside the TV about adjusting this setting in fact most pots are set at he factory and glued so you can't accidentally adjust them if they even provide them ))) And the funny thing with X-rays there really is no Annoyance, you don't know whats going on until the damage is done.... Now the noise until it reaches 85 dB (A) which is the 8 hour limit for a five day week in most of the world, which has established safety standards, there honestly is no major issues, and if the TV is outputting 85 db there is some thing wrong with the audio section or the tv station is broadcasting that tone... A scan transistor would be very very very hard pressed to generate a sound pressure level that high without destroying itself even the flyback would be hard pressed to generate that high of a SPL... (( and just to clear up how loud 85 db is, it's about as loud as an alarm clock or vacuum cleaner at one meter )) a fridge is 50 db and it annoys me but is it a hazard to my hearing, nope not a chance ))

the limit does not mean its safe. it means only that the damage is below some amount that is considered acceptable same goes for norms of air pollution and other stuff to see what im speaking about build a circuit that outputs a constant high pitched noise (or do it on the computer) and try to be in the same room with it for few days (in windows 98 you can make constant beep if you run debug and enter there 'o 61 ff' ('o 61 0' to stop). in newer windows maybe too) the fridge does not come any close to the same effect

How do you figure a fridge is not close ? I set up a SPL meter and a 15.734 kHz audio source ( simple sine wave ) at 50 db ( A-weighted so the meter replicates the human ear ) it is just as annoying as the fridge, only it's more directional but only because the fridge is outputting a lower frequency..And because of reflection from walls and other hard surfaces you get louder and quieter spots ( Interference ) but the change in SPL is not that much .. Now will there be any long term damage to my hearing ?? Nope it's not loud enough, you playing with sound pressure levels that are similar to humans talking to each other at a distance of about a meter ( 40 to 60 db ( A-weighted ) it's quieter then a screaming baby ....

the 15 KHZ is at the very edge of your hearing and is source of stress the 50 or 100 HZ and whatever mechanical sounds he fridge makes are not

life itself is stressful... simply adding a little noise isn't going to kill you and the sound pressure level will not give you even temporary damage to your hearing and it's not sufficient to give you long term damage either.....

the sound is stressfull on the hearing (as in mechanical stress) not on the soul

My monitor is fine, like the picture displays perfectly except for a scan line that I can see every once in a while. But yeah the display is working its jsut the high pitched whine.

you have that TV. you may : 1. fix it to make it silent 2. replace it 3. keep living with it ignoring the noise 3 is not an option

Depending on your age, mostly. Most people over 30+ years of age (32 I think the average is) can not hear sounds above a certain frequency. There is the occassonal oddball around, the exception (:-) but for the most part, it just happens as we age.

No as you get older you lose your high frequency part, this is why your teachers can't hear the mosquito ring tone (( well ok most of them can't ))

Yard Sale! "Runs Good!" Then go buy another one!

But its so big :( and im but a lowly high school student on a budget?

Same here. You could start a business repairing televisions!

Ok what you need to do is post the model number and chassis number if you have one, also a local library is good place to find older schematics, there is some websites as well, what your looking for a scan transistor, normaly it will be a TO-263 or TO-220 and may have a cut tab ?? it's hard to say but those a re the most common cases of large power transistors used in TV's, commonly they are marked on the PCB, with areas like High voltage, PSU, H scan V scan sections.. The section your looking for should be marked Horizontal Frequency or some thing to that effect and it is 15.734 kHz, (( NTSC -M standard, which is the standard in North America )) what you can do is cross reference the transistor numbers with a better / different model, and if you get a better / different transistor with similar electrical ratings, it might get rid of the noise, this is not always 100% effective, TV's are made so fast and so cheap thing's tend to get over looked and parts can be over driven and bad things happen like noise........

sounds like noise from the flyback. maybe its made by the dust on the high voltage parts - im unsure

open the TV and blow all the dust away with a compressor (no air spray and the like. use real compressor)

dont get close to the parts if you dont discharge the high voltage first. it may flash over air distance (10 cm = min distance that i think is safe. 1 cm if you do discharge it)

Well it is in a VERY dusty area near a brick wall so that could be the dust and the brick particles gettign inside the TV. Do you think I can use a variable compresser to blow the stuff around?

Did you try kicking it?

You know, all of your response to all form topics would be different if ur avatar was different. I read what you say, then I see your avatar, and then I'm like lol just had to say that lol

i wanted to adjust it with my mood for that day but i realized I was lazy don't worry, most of my comments are meant as jokes

I was also thinking that maybe it could possibly be the actual cable as in "Cable TV" cable because my friend was the one who crimped and put a new connecter onto the cable. He could have possibly crimped the wire wrong could that effect it?

. No. . Use a directional mic to zero in on where it's coming from.