ffang@umaxc.weeg.uiowa.edu (Francis Fang) (06/02/91)
I've got a 2 year old 27" Sony TV that has been great except for recently when I've noticed that there is a semi-loud high pitch squeal that accompanies the operation of the set. Does anyone out there have any suggestions for probable cause? Thanks in advance.
kludge@grissom.larc.nasa.gov ( Scott Dorsey) (06/03/91)
In article <6298@ns-mx.uiowa.edu> ffang@umaxc.weeg.uiowa.edu (Francis Fang) writes: >I've got a 2 year old 27" Sony TV that has been great except for recently >when I've noticed that there is a semi-loud high pitch squeal that accompanies >the operation of the set. Does anyone out there have any suggestions for >probable cause? Bets are that what you are hearing is the vertical sweep oscillator. If so, you should be happy that your hearing responds to such high frequency. Possibilities are that the flyback transformer has begun to vibrate slightly, or one of the capacitors has begun to vibrate at that frequency. If you take a tube puller and put some cotton on it, you should be able to go around and grab components in the sweep circuit until you find the one that's doing it. Bets are good that it's on the flyback. Of course, you could always go to a couple of good, loud rock concerts and eliminate your high frequency hearing. --scott
falcon@hubcap.clemson.edu (james lysaght) (06/03/91)
A high pitched squal is a common aging problem in electronics. The past two TV's I have owned have had that problem but they lasted closer to 5 years. I researched the problem (i'm an Electrical Engineer). My TV is solid state so I only researched solid state and will only comment on those. Every solid state TV has a little transistor (little as in microchips) which serves to prevent this squal. The squal occurrs when, over time, the transistor burns out and no longer functions. You are correct in saying it is the verticle sweep but you can not stop the verticle sweep oscillation (and still have a picture). So, the remedy... buy a new TV. It is cheeper to replace than fix (usually). Disclaimer.... this all based on the idea that your high pitched squal is the same as my high pitched squael (notice I can't spel squael, squeele, or whatever) Jim Lysaght
kludge@grissom.larc.nasa.gov ( Scott Dorsey) (06/04/91)
In article <1991Jun3.163755.825@hubcap.clemson.edu> falcon@hubcap.clemson.edu (james lysaght) writes: > You are correct in saying it is the verticle sweep but you can not stop the verticle sweep oscillation (and still have a picture). So, the >remedy... buy a new TV. It is cheeper to replace than fix (usually). First of all, I was not correct in saying it was the vertical sweep. It's the horizontal sweep and my brain was not correctly engaged at the time I was making the original posting. Second of all, very few things are cheaper to replace than fix, if you do the work yourself. In addition, you get the satisfaction of having done something well, and knowledge about how things work. Something like this, which is probably a delaminating coil or a capacitor that is vibrating isn't difficult at all to fix and if you find it annoying, is worth fixing. --scott
jeh@cmkrnl.uucp (06/07/91)
In article <1991Jun3.163755.825@hubcap.clemson.edu>, falcon@hubcap.clemson.edu (james lysaght) writes: > I researched the problem (i'm an Electrical Engineer). My TV is solid state > so I only researched solid state and will only comment on those. Every > solid state TV has a little transistor (little as in microchips) which > serves to prevent this squal. Rubbish. > The squal occurrs when, over time, the transistor burns > out and no longer functions. Rubbish. > remedy... buy a new TV. It is cheeper to replace than fix (usually). You might actually be correct here, unless the set is very expensive. horizontal-sweep squeal (note spelling) can be very difficult and expensive to track down and fix... particularly since many technicians can't hear it! rec.video has had several accounts from people who reported that their tv is making a high-pitched whine, but techs could find nothing wrong. (A tv tech's high-frequency hearing deficiency is likely due at least partly to working around tv sets day in and day out!) The source may be the flyback transformer, the deflection yoke, or even a printed circuit board (not necessarily components on the board, but the board itself). Someone else mentioned capacitors. Once you find the offending part, then what? If it's something like a capacitor or a PC board, you may be able to tie it down or wedge it or something so that it can't vibrate. If it's the flyback or deflection yoke, replace it. Some people have suggested potting these components, but this is not a good idea; they would run very hot afterward and so have a vastly shortened life, meaning that you'll end up doing the replacement anyway. Oh, and it's the horizontal sweep, not the vertical. The vertical is at 60 Hz (well, 59.93) and in no way could be considered "high pitched". But it too is audible in many sets, as a low-pitched buzz. --- Jamie Hanrahan, Kernel Mode Consulting, San Diego CA Chair, VMS Internals Working Group, U.S. DECUS VAX Systems SIG Internet: jeh@dcs.simpact.com, hanrahan@eisner.decus.org, or jeh@crash.cts.com Uucp: ...{crash,scubed,decwrl}!simpact!cmkrnl!jeh
ifaq570@ccwf.cc.utexas.edu (Allen Kitchen) (06/08/91)
Another common problem that causes that squeal is dust on, in, and around the flyback and the anode cable. Apparently the dust is attracted to any leakage, and this gives a convienient path for small arcing to form. I know I cleaned off the cables on my 1982 RCA, and it has been silent for a long time now. By the way, before you clean it, make sure you aren't grounded, and that the set is unplugged. If possible, short out the anode cable to the chassis ground first. People do funny things when hit with this kind of voltage ( I didn't, but I'm a Tech ). allen
durham@w2xo.pgh.pa.us (Jim Durham) (06/09/91)
In article <1991Jun7.030706.85@cmkrnl.uucp> jeh@cmkrnl.uucp writes: >In article <1991Jun3.163755.825@hubcap.clemson.edu>, >falcon@hubcap.clemson.edu (james lysaght) writes: >> I researched the problem (i'm an Electrical Engineer). My TV is solid state >> so I only researched solid state and will only comment on those. Every >> solid state TV has a little transistor (little as in microchips) which >> serves to prevent this squal. > >Rubbish. I agree, although I would have phrased it differently! 8-) . > >> The squal occurrs when, over time, the transistor burns >> out and no longer functions. > >Rubbish Now c'mon...little squeal suppressor? I've got my pants legs rolled up..but.. > >horizontal-sweep squeal (note spelling) can be very difficult and expensive to >track down and fix... particularly since many technicians can't hear it! I have to deal with these things on a regular basis. The way I find the offending part is to use a rolled-up sheet of paper or a drinking straw. It is pretty directional at 15khz and , if you put one end in your ear (carefully!) and wave the other end around the vicinity of the flyback and horizontal output components, you should shortly be able to discover the component that is squealing. Most times it is the flyback transformer. I have seen these fixed by driving small wooden wedges in between the winding and the core. Yes..a lot of people can't hear 15 khz. These are probably the same ones who go around worrying about "aliasing noise" on a CD 8-) ! . One other thing. If the picture is not tearing or unstable, the above advice is useable. If there is a multi-frequency sound to the squeal (low frequencies mixed in with the 15khz), then you could have a horizontal oscillator problem. The flyback will not like foreign frequencies and will protest. However, you should see some indication of this in the picture. If you *do* have a "dirty" sounding squeal and picture problems, then the only thing is to get out a scope and look at the horizontal waveform and see if it is a nice clean sawtooth. If not, fix the oscillator or output stage. This phenomenom is called "sqeegying" of the oscillator by tv tech types. -Hope this helps. Jim Durham (durham@w2xo.pgh.pa.us)
ttrueger@athena.mit.edu (Timothy T. Rueger) (06/10/91)
In article <1991Jun7.030706.85@cmkrnl.uucp> jeh@cmkrnl.uucp writes: (Regarding a squealing TV...) >horizontal-sweep squeal (note spelling) can be very difficult and expensive to >track down and fix... particularly since many technicians can't hear it! > >The source may be the flyback transformer, the deflection yoke, or even a >printed circuit board (not necessarily components on the board, but the board >itself). Someone else mentioned capacitors. > >Once you find the offending part, then what? If it's something like a >capacitor or a PC board, you may be able to tie it down or wedge it or >something so that it can't vibrate. And that is exactly how I solved my particular TV squeal. I found the offending part, and wedged a wooden clothespin (!) between the part and the picture tube. A low-tech solution if ever there was one. When it fails, I'll finally break down (ugh...) and get a new set. > --- Jamie Hanrahan, Kernel Mode Consulting, San Diego CA -Tim _______________________________________________________________________ Tim Rueger - TA, 6.775 - Analog MOS Design Office: 24-312, 258-5691 Email: ttrueger@athena.mit.edu Home: Westgate 1609, 494-9414 ttrueger@ed.mit.edu
wolfgang@wsrcc.com (Wolfgang S. Rupprecht) (06/13/91)
> Another common problem that causes that squeal is dust on, in, and > around the flyback and the anode cable. Apparently the dust is attracted > to any leakage, and this gives a convienient path for small arcing to > form. I know I cleaned off the cables on my 1982 RCA, and it has been silent > for a long time now. By the way, before you clean it, make sure you aren't > grounded, and that the set is unplugged. Being grounded in the formal sense or not doesn't matter AT ALL when we are talking about 10's of kV. If you happen to touch the HV section on your TV, and it is still charged up, you will get knocked on your butt. Perhaps permanently. > If possible, short out the anode > cable to the chassis ground first. People do funny things when hit with > this kind of voltage ( I didn't, but I'm a Tech ). If possible???? You are kidding, right? BY ALL MEANS ground the HV capacitor to if you are planning on messing with the HV section. Especially if you are planning on wiping the HV lead with a damp cloth! Keep the shorting strap in place during the whole time you work on the set. Charge will bleed back from the glass parts of the CRT onto the internal capacitor plates. Remember these simple rules when working around HV: 1) Keep your left hand in your back pocket. This way you won't be tempted to use it and complete a circuit should you drop something and reflex action causes you to make a grab for it. 2) Always attach a ground wire to a well connected metal part of the device. You will obviously want to attach the ground end of the wire first. 3) Now attach the ground wire to HV capacitor - you will hear a snap if it was really charged up. If it only had a few kV's on it you probably won't hear the snap. Leave this ground attached till you are done! -wolfgang PS. I have had excellent results with RTV, and/or Crazy Glue for fixing loose parts that have caused H-sweep squeal. Crazy glue works like a champ at re-laminating loose flyback parts. RTV really absorbs the high frequency energy that still happens to make it out. Together they are a great combination. -- Wolfgang Rupprecht wolfgang@wsrcc.com (or) uunet!wsrcc!wolfgang Snail Mail Address: Box 6524, Alexandria, VA 22306-0524
jeh@cmkrnl.uucp (06/16/91)
In article <1991Jun13.160527.4094@wsrcc.com>, wolfgang@wsrcc.com (Wolfgang S. Rupprecht) writes: >> If possible, short out the anode >> cable to the chassis ground first. People do funny things when hit with >> this kind of voltage ( I didn't, but I'm a Tech ). > > If possible???? You are kidding, right? BY ALL MEANS ground the HV > capacitor to if you are planning on messing with the HV section. > Especially if you are planning on wiping the HV lead with a damp > cloth! Keep the shorting strap in place during the whole time you > work on the set. Charge will bleed back from the glass parts of the > CRT onto the internal capacitor plates. I highly agree with your basic point -- that you should ground the HV lead -- but I'm not sure what "capacitor" you're talking about here. The CRT in a tv set *is* the HV capacitor. The second anode coating on the inside of the "bell" of the CRT, plus a similar, grounded coating on the outside, forms the capacitor. (Not much capacitance, but extremely high voltage and low leakage. Those who remember the static electricity parts of Physics 101 will note the resemblance to an old-fashioned Leyden jar.) In very old sets (those that use a tube for the high voltage rectifier) the CRT could hold a dangerous charge for weeks! In modern sets, there is enough leakage back through the HV rectifier diode to drain the charge to a safe level in "only" a day or two... The usual procedure for grounding the HV lead is to use a screwdriver with a long plastic (not wood) handle. Attach a clip lead to the blade shaft and to chassis ground, hold it by the end of the handle, and gently poke the blade under the HV connector's "skirt". You will hear a snap as the charge arcs to the blade. You're not done yet; push on until the blade firmly touches the connector, and leave it there while you work on the set. In a similar vein... when working on photoflash units you will find that the capacitor holds a hefty charge at several hundred volts. After reading the above, you may be tempted to short the capacitor with a screwdriver blade in order to avoid a nasty shock. Don't do it! Photoflash capacitors can be damaged if they're discharged into a dead short. Use a 10K resistor instead. --- Jamie Hanrahan, Kernel Mode Consulting, San Diego CA Internet: jeh@dcs.simpact.com, hanrahan@eisner.decus.org, or jeh@crash.cts.com Uucp: ...{crash,scubed,decwrl}!simpact!cmkrnl!jeh