TV problem

[Tom41]

My big TV, after many years of service, has finally given up on me. When I push the power button, nothing comes on the screen, the power LED lights dimly and there is a LOUD buzz from the loudspeaker. The buzzing continues until I turn the power off again - it sounds rather like a motorcycle revving up and down.

Power on - buzzing starts, rising to a pitch
Power off - buzzing lowers in pitch and finally stops.

Sometimes if I keep turning the power off and on, it will eventually start up. But it's a chance I don't want to take when turning it on to watch programmes at 6am!

It sounds to me like something is energising and then cutting out straight away, causing the normal 'pop' from the loudspeaker to turn into a loud buzz. Perhaps the caps have bulged/burst/dried out, but I haven't opened it up to look yet.

I do have a spare TV (thankfully), but that's also got a problem - the color level keeps changing, and sometimes alters if I touch the front panel buttons! Loose connection somewhere?

[Rainbow]

Re: TV problem

It looks like some caps in the power supply dried out.

[Decade]

Re: TV problem

As Rainbow stated dried out caps could cause this but check for any cold solder joint around the HV transformer or in the psu, could be lots of things.
What brand model?

[arneson]

Re: TV problem

Had a bad thunderstorm recently?
That kind of problem is often found in the vicinity of the power cord.
Diodes are very much suspect and vreg chip.

[chipper]

Re: TV problem

Usually , bad capacitors would not allow the transformer to power up at all , and a pause would be followed by a complete shutdown (refusal to run). If the transformer is worn out , you will hear a high pitched screaming sound , that is audible in the speakers because of the transformer short circuit in the winding.

This is not always the case , because a very badly blown or open capacitor can cause the transformer to act like it is not powering up in extreme cases. I have even had an older amplifier cause the exact same circumstances when it had been heating up during operation so much that it had warped the circuit board it was mounted to. Because the board was curved , heat eventually caused the dried out solder on 1 corner to loosen and eventually become (uncontacted by the base connectors). When the unit cooled , it worked , but went off within half an hour. When I opened it , I saw the corner (loose) , so I powered on the unit after cooling and pushed the transformer back into it's leg slot with a piece of thin wood. The unit kept working , but required a large solder and resetting job to make it stay flat on the board and connected.

This was all because the 1 leg solder was grounding the audio power ic's in the traces.
Once done the transformer worked with volume , but still did make a slight whistling or whining sound , without speaker interference below full volume. In this case , it meant that the transformer was near it's end of it's lifespan and needed replacing.

So , in other words , when you hear whistling coming from a transformer , it is usually shot , and replacing it will remove the sound completely. The capacitors only store voltages provided by the transformer for use in the circuits.

[chipper]

Re: TV problem

The color changings from the front buttons are the flyback settings being sensitive to any input voltages or amperages. You need to check the flyback setting screws on the side of the tv where the red wire with the tube boot on it goes into. If the tv allows put a screwdriver in the black setting knobs and turn them to set base colors.

Make sure that you set the brightness to as high as the set will allow and still be visible before you set the colors in the flyback control to lower the color settings. This will cool the flyback down and make it less sensitive , but it is on the way out if it wasn't badly maladjusted in the first place. Contrast should be used to sharpen the picture , not brighten it after everything is set low. The high settings are supposed to be on the controls only , not by setting the flyback high and the set high. It leads to whistling or humming and heat sensitivities. (low current overload)

[chipper]

Re: TV problem

The standard procedure for setting colors , on any tv , including laser or color wheel sets , is to set the brightest color first , then the other 2 as they compare for brightness. This is according to service manual specifications , to ensure highest brightness without overload to flyback. (less heat - longer life)

The same thing is applied to brightness , it should be set high so that the flyback has less current flowing to each color production circuit before setting color density.

All tv and remote controls : tint / contrast / color / sharpness and alike are for adjustment only , and should not be used to increase the base color density , but to decrease any over brightness or color density overloads at different settings.

Controls are for turning the settings down , not up in general.