Arcing, sparking CRT High Voltage Cable

[Thabto]

I am repairing a Sharp 21” CRT TV (Model 21D1-S). When I switch it on, everything is functional. Except that there is a crackling, acing sound you hear coming from inside the TV. I removed the back cover once, and switched it on in a dark room, and saw a blue flame on the HV cable. I covered the affected are with insulation tape and the flame was gone, but what's left is the crackling noise. It seems it increases with time from the moment the TV is switched on; beginning on 30 seconds. Tested for faulty components, all seem fine. Could this mean I need a new flyback transformer?

[berniedd]

Re: Arcing, sparking CRT High Voltage Cable

You're hearing a high voltage arc. If it's from the inside of the flyback transformer, replacement is the only practical resort. If it's on the outside of the flyback transformer or high voltage cable, you should see it with the room darkened. It can be fixed by a coating of special high voltage corona dope/cement. However, unless you know exactly what you're doing, I would suggest you leave it to the experts. That thing develops up to 40,000 volts and can give you a nasty shock.

[Krankshaft]

Re: Arcing, sparking CRT High Voltage Cable

Replacing the flyback is the only option if insulation has deteriorated on the cable you can bet it has deteriorated elsewhere inside the flyback.

It's possible that the arcing from the anode wire caused heating of the HV winding which caused some of it's insulation to fail.

The HV anode flyback windings are thinner than a human hair and their insulation is even thinner so it doesn't take much to damage them.

Some flybacks begin arcing from old age without any outward cause or just die outright preventing the chassis from powering up. They are the next most susceptible part to fail in a TV with number one being the Horizontal Output Transistor.

While it's most likely the flyback since you had arcing from the anode wire. The only other thing it could be if it's not the flyback is the deflection yoke arcing to the CRT dag due to failed winding insulation. If this is the case junk the TV it's not worth fixing.

Open the chassis and listen to where the noise is coming from.

Here is a site to find out if your flyback is still available:

http://www.encompassparts.com/

They're my go to source for major brand repair parts. If they don't have it you're going to have a pain finding it .

[tmwalsh]

Re: Arcing, sparking CRT High Voltage Cable

I would take a dry cloth and clean the dust from the HV [red] fat wire leading to the crt and around the suction cup and surface of the crt nearby. You would then be removing the 'track' is uses for conductivity.

I would also determine where the noise is coming from using a piece of hose held near my ear and POINTING at spots on the set. Do NOT touch the set when it is powered up.
You have two other possibilities besides arcing internal to the flyback transformer: 1)arcing occurring in the cup embedded in the tube due to the metal connector not touching the cup or 2)arcing to the coating on the tube [aquadag] coming out from under the rubber 'suction cup' that is mushed flat against the tube near the cup.
Sometimes, cleaning and reseating the cup & connector can stop the arcing, or you can try using the spray on products that 're-insulate' the wire or cup. Some you spray on top of the suction cup while it is in place.
tom

[hardwareguy]

Re: Arcing, sparking CRT High Voltage Cable

Discharge the CRT and thoroughly clean the HV lead with a cloth and rubbing alcohol.

Once dry, use GE Slilicone II or equivalent 100% silicone sealant to seal the area where the arc happened. Spread the sealant 4cm or so beyond the insulation crack, both before and after the crack.

The silicone layer needs to be 1mm thick at the minimum. Coat this with electrical tape and seal the tape with silicone.

Let the silicone dry overnight before powering the set up...its insulating properties are better once dry.

[i4004]

Re: Arcing, sparking CRT High Voltage Cable

>to seal the area where the arc happened

he doesn't see that area, it's inside the flyback, so he can't do that.

[delaware74b]

Re: Arcing, sparking CRT High Voltage Cable

He should replace the flyback because if it starts to short the windings, there will be more to replace than just the flyback, such as the horizontal output transistor. The RCA's are very likely to take out the HOT when the flyback fails. Voice of experience and well-documented in this forum and other forums on internet.

[stj]

Re: Arcing, sparking CRT High Voltage Cable

the arc will carbonise the insulation creating an extra conduction-path.

just replace it with a clone from HR,Philex,Eldor,Konig or one of the other "duplicators"
most cost under €20.