TV buzzes with overly white video

[Steve Kraus]

Sony KV-27EXR25, probably 14 or 15 years old. Back in 2004 I replaced a
failed regulator with help from this NG.

In the past few months I've been getting a loud buzz at certain instances
when there's some overly white video. Picture flops around a bit too.

It's directly on analog cable and I don't doubt that Comcast may
occasionally have signal levels that are out of spec but it doesn't seem to
bother other sets in the house including one that is a similar Sony, maybe
a few years older even. So I'm wondering if something is out of whack on
the TV. Is there a solution (besides the eventual upgrade to digital HD
flat screen)?

 

[JANA]

Perform an ESR test on the caps in the power supply area, and especially in
the area where the IF and tuner sections are.

--

JANA
_____


Sony KV-27EXR25, probably 14 or 15 years old. Back in 2004 I replaced a
failed regulator with help from this NG.

In the past few months I've been getting a loud buzz at certain instances
when there's some overly white video. Picture flops around a bit too.

It's directly on analog cable and I don't doubt that Comcast may
occasionally have signal levels that are out of spec but it doesn't seem to
bother other sets in the house including one that is a similar Sony, maybe
a few years older even. So I'm wondering if something is out of whack on
the TV. Is there a solution (besides the eventual upgrade to digital HD
flat screen)?

 

[bg]

Sony KV-27EXR25, probably 14 or 15 years old. Back in 2004 I replaced a
failed regulator with help from this NG.

In the past few months I've been getting a loud buzz at certain instances
when there's some overly white video. Picture flops around a bit too.

It's directly on analog cable and I don't doubt that Comcast may
occasionally have signal levels that are out of spec but it doesn't seem to
bother other sets in the house including one that is a similar Sony, maybe
a few years older even. So I'm wondering if something is out of whack on
the TV. Is there a solution (besides the eventual upgrade to digital HD
flat screen)?

whites are saturating, this causes the buzz - adjust the AGC

 

[webpa]

Sony KV-27EXR25, probably 14 or 15 years old. Back in 2004 I replaced a
failed regulator with help from this NG.

In the past few months I've been getting a loud buzz at certain instances
when there's some overly white video. Picture flops around a bit too.

It's directly on analog cable and I don't doubt that Comcast may
occasionally have signal levels that are out of spec but it doesn't seem to
bother other sets in the house including one that is a similar Sony, maybe
a few years older even. So I'm wondering if something is out of whack on
the TV. Is there a solution (besides the eventual upgrade to digital HD
flat screen)?

Called a "sync buzz". Caused by white video being out of
specification...or by the receiver's audio section being out of tune.
Your Sony may have old-fashioned IF cans/coils, for video and sound IF
and AGC. If so, then just tune it up. Naturally, you'll need service
data or lots of experience. Or both. If your Sony is all digital, it
will take some specific devices and jigs to tweak the alignment.

 

[Mark]

Sony KV-27EXR25, probably 14 or 15 years old.  Back in 2004 I replaced a
failed regulator with help from this NG.

In the past few months I've been getting a loud buzz at certain instances
when there's some overly white video.  Picture flops around a bit too.

It's directly on analog cable and I don't doubt that Comcast may
occasionally have signal levels that are out of spec but it doesn't seem to
bother other sets in the house including one that is a similar Sony, maybe
a few years older even.  So I'm wondering if something is out of whack on
the TV.  Is there a solution (besides the eventual upgrade to digital HD
flat screen)?

Find the sound QUAD coil or discriminator coil and give it a little
tweak until the sound clears up.

If all your TVs buzz on a certain channel when there is heavy white in
the screen, then call Comcast and thell them they are overmodulating
the video.

Mark

 

[[email protected]]

too.

Find the sound QUAD coil or discriminator coil and give it a little
tweak until the sound clears up.

Don't dick with the RF alignments. Someone already pointed out the AGC
is a strong culprit. If that doesn't do the trick, I'd want the whole
IF swept to find out what is _really_ going on.

If all your TVs buzz on a certain channel when there is heavy white in
the screen, then call Comcast and thell them they are overmodulating
the video.

Mark

GG

 

[N Cook]

Sony KV-27EXR25, probably 14 or 15 years old. Back in 2004 I replaced a
failed regulator with help from this NG.

In the past few months I've been getting a loud buzz at certain instances
when there's some overly white video. Picture flops around a bit too.

It's directly on analog cable and I don't doubt that Comcast may
occasionally have signal levels that are out of spec but it doesn't seem to
bother other sets in the house including one that is a similar Sony, maybe
a few years older even. So I'm wondering if something is out of whack on
the TV. Is there a solution (besides the eventual upgrade to digital HD
flat screen)?

No one has established from the OP whether noise from the speaker or direct
from the back.
My TV has always buzzed on peak whites, a sort of metallic buzz, presumably
not from the LOPT as no other problems. I've never had a more pressing
reason to get in there and explore. Almost as though the scan coils are
moving but that would not respond to beam current variation

 

[Steve Kraus]

No one has established from the OP whether noise from the speaker

Buzz is in the audio from the speaker.

I'd like to explore the AGC issue before messing with anything else. Is
this something that has a physical adjustment? That would seem to be the
way to go with least downside if it's wrong.

BTW, how do you get into the setup/service menu? I've tried pushing the
button via the small hole in back but it doesn't seem to do anything.
Again, this is a Sony KV-27EXR25. If the service manual is available free
online anywhere please point me.

Also, if it is an AGC issue would putting a pad on the RF (cable) input
solve it in simple fashion? Right now I have the cable looped through a
VCR (pass through) hoping it might help and maybe it has but not enough.

 

[[email protected]]

Buzz is in the audio from the speaker.

I'd like to explore the AGC issue before messing with anything else.  Is
this something that has a physical adjustment?  That would seem to be the
way to go with least downside if it's wrong.

BTW, how do you get into the setup/service menu?  I've tried pushing the
button via the small hole in back but it doesn't seem to do anything.  
Again, this is a Sony KV-27EXR25.  If the service manual is available free
online anywhere please point me.

Also, if it is an AGC issue would putting a pad on the RF (cable) input
solve it in simple fashion?  Right now I have the cable looped through a
VCR (pass through) hoping it might help and maybe it has but not enough.

A pad shouldn't help as the 'automatic gain control' will just push up
the gain to make up for the pad. If it's in an extremely high RF
condition, the pad might help but it's rare to get that much signal.

GG

 

[Michael A. Terrell]

A pad shouldn't help as the 'automatic gain control' will just push up
the gain to make up for the pad. If it's in an extremely high RF
condition, the pad might help but it's rare to get that much signal.

GG

Have you ever tried a pad? The AGC system in a TV is a very basic
system that is designed to keep the level within a range, and driving it
to the upper limit can cause sync buzz. I have seen complex AGC systems
with 14 op amps, and the DC offset was limited to 1.5 mV over the entire
range. It could maintain the output level to less than a .1 dB change
over the entire useful RF input range. You WILL NOT see a AGC system
like this in a consumer level receiver.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[[email protected]]

   Have you ever tried a pad?  The AGC system in a TV is a very basic
system that is designed to keep the level within a range, and driving it
to the upper limit can cause sync buzz.  I have seen complex AGC systems
with 14 op amps, and the DC offset was limited to 1.5 mV over the entire
range.  It could maintain the output level to less than a .1 dB change
over the entire useful RF input range.  You WILL NOT see a AGC system
like this in a consumer level receiver.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Yeah I've tried pads and they do make a difference if the signal is so
strong as to overload the front end but as I said earlier, that
condition is not very common. More common for the AGC to be pushing
the visual carrier to cutoff causing the buzz.

GG

 

[Steve Kraus]

Yeah I've tried pads and they do make a difference if the signal is so

strong as to overload the front end but as I said earlier, that
condition is not very common. More common for the AGC to be pushing
the visual carrier to cutoff causing the buzz.

How would I adjust it or is that even possible? I'm hoping for a little
trimpot in there but I don't have a schematic.