Sanyo 27" CRT TV speakers have intermittent static noise during operation

[CRTguy]

I have a 27" Sanyo CRT TV from the year 2000 and during operation, the TV speakers produce static noise that is intermittent. It does this whether I have a video source connected or not. The static noise mostly goes away during darker scenes in a video but if the picture gets bright or there is a lot of white text on the screen the static noise comes back and is much louder. I used to own the same exact Sanyo model a few years ago and that TV also had the static noise problem.

Does anyone have any idea what could be causing this and if it can be fixed? I know I could just disconnect the TV speakers internally but the TV has nice sound and I would like to fix it if I could.

[Alex KL-1]

Is like a constant annoying noise if you freeze the image with the offending video content?
Some amps in some TV's are indeed ssensitive to that. I have a Telefunken that I decided to make some shield in the amp (using some solderable metal soft mesh), since is close to the video output. Worked like a charm.

[CRTguy]

That is correct. When the offending video content is displayed, the static noise gets louder and is constant. More specifically, anytime a bright scene or lots of white text is displayed on a dark background. That is an interesting idea about the shield. Where would I solder the shield to?

[Alex KL-1]

You can solder it to the ground of the audio output (I imagine that being a IC). WIth short wire to it. Avoid it touching anything. Alternatively, fixing it to the IC heatsink also may work.
But, if insufficient to isolate the audio sector in this plane (above PCB), some shield below the PCB where the audio circuits are located will help, also.
In sum, any shield between the video out cables and circuits and the audio circuits.

Unless the audio are coming from a "jungle" IC having bad surrounding ground layout; then, is more difficult to solve.

[old_tv_nut]

Alex, this is the first time I've heard of interference from video into audio at baseband. Very interesting.

The more common thing in older sets was sound buzz due to IF/sound misalignment - tends to occur when bright sharp details are present, like white letters.

[damen]

Loose or completely disconnected dag grounds on the CRT will sometimes cause this symptom.

[Alex KL-1]

Originally Posted by damen

Loose or completely disconnected dag grounds on the CRT will sometimes cause this symptom.

+1, worth checking

[Alex KL-1]

Originally Posted by old_tv_nut

Alex, this is the first time I've heard of interference from video into audio at baseband. Very interesting.

The more common thing in older sets was sound buzz due to IF/sound misalignment - tends to occur when bright sharp details are present, like white letters.

Really, very uncommon, in fact, but I testified some with that symptom in my life.
Since especially some audio IC's are prone to demodulating HF signals at input or feedback junctions (normally at inputs, due to lenght of needed traces). Strategically local input decoupling can help, also (eg. some ceramic cap to local audio ground at offending inputs). Not all sets follows good audio practices...

[CRTguy]

Originally Posted by old_tv_nut

Alex, this is the first time I've heard of interference from video into audio at baseband. Very interesting.

The more common thing in older sets was sound buzz due to IF/sound misalignment - tends to occur when bright sharp details are present, like white letters.

Would a sound misalignment contribute to the buzzing being intermittent and being present whether there is a video source connected or not?

I don't have any equipment to do an IF/sound alignment. Is this something where I could adjust the sound/IF transformer and do it by ear to see if the buzzing goes away when I make an adjustment?

[old_tv_nut]

Originally Posted by CRTguy

Would a sound misalignment contribute to the buzzing being intermittent and being present whether there is a video source connected or not?

I don't have any equipment to do an IF/sound alignment. Is this something where I could adjust the sound/IF transformer and do it by ear to see if the buzzing goes away when I make an adjustment?

1) If this is not an old tube set, my comment doesn't apply.
2) Do not touch any alignment adjustments without the right equipment. You will only make it worse. The only things that are safe to try are an AGC control or a sound buzz control if the set has one (typically on old tube Zeniths, I think).

When you say video source are you referring to a RF antenna source or RCA composite input? A buzz affected by IF alignment would come and go according to different image content on an antenna signal. If it is doing it on composite input or doing it randomly independent of the video content, then it's something besides alignment, quite possibly grounding or shielding between circuits.