Can a cable TV signal break a TV tuner?

[Tony Sivori]

I've had two TVs break in a very similar fashion, and both were plugged
into the exact same cable.

The first was a Toshiba, all the lower channels (2 through about 8) took
multiple tries to get them to come in clear. It was like the signal was
drifting. The rest of the channels were fine.

So I replaced the Toshiba with an RCA that had given good service for over
10 years. Within a few months, it has a nearly identical problem. All the
lower channels are now pure snow, but the rest still work perfectly. It
won't get lower channels on broadcast, either.

So I've replaced the RCA with a used Sharp, and I'm almost expecting it to
go bad.

Obviously, three TVs in a row breaking in the same way would all but prove
that something was up. But in the meantime, any guesses? Was it probably
coincidence that two TVs in the same location failed in a very similar
manner? Or might the cable be somehow partly breaking the tuner?

 

[- - ex - -]

I've had two TVs break in a very similar fashion, and both were plugged
into the exact same cable.


Obviously, three TVs in a row breaking in the same way would all but prove
that something was up. But in the meantime, any guesses? Was it probably
coincidence that two TVs in the same location failed in a very similar
manner? Or might the cable be somehow partly breaking the tuner?

Well, from an RF perspective its impossible. Period. However, from the
standpoint of ground loops resulting from spliced-in unauthorized
connections and/or improper bonding or grounding its very plausible.
The cable people typically won't be much help in this scenario.
As a cable guy for multi years I'd suggest visually tracing the line
right back to the tap and see if anybody has 'messed' with it. If
nothing awry is found I personally would write it off as happenstance.
Any number of scenarios can develop regarding household voltage surges,
weak grounds on the customer's premises and most of such scenarios
reveal themselves by simple visual inspection.
The wiring merits inspection but in my experience I'd vote for
'coincidence' unless there is an obvious wiring fault to the contrary.

-Bill M

 

[Tony Sivori]

Well, from an RF perspective its impossible. Period. However, from the
standpoint of ground loops resulting from spliced-in unauthorized
connections and/or improper bonding or grounding its very plausible. The

Thanks for the info. I'm somewhat familiar (I'm studying for a Network+
certification) with ground loops causing problems with regard to computer
LANs using coax; grounding both ends of the coax is the cause of the loop.
How would this circumstance arise in a cable TV setting? There are no
provisions that I'm aware of to ground the TV end of the cable.

cable people typically won't be much help in this scenario. As a cable
guy for multi years I'd suggest visually tracing the line right back to
the tap and see if anybody has 'messed' with it. If nothing awry is
found I personally would write it off as happenstance. Any number of
scenarios can develop regarding household voltage surges, weak grounds
on the customer's premises and most of such scenarios reveal themselves
by simple visual inspection. The wiring merits inspection but in my
experience I'd vote for 'coincidence' unless there is an obvious wiring
fault to the contrary.

That is interesting. The TVs in question are in my mother's house, she had
three outlets, but after signal strength problems (on upper channels) the
cable company disconnected one of the three outlets (it was no longer
used). The timing would be about right; that is, the first TV broke a few
months after the third outlet was disconnected. Might something the
serviceman did be the cause? If so, what should I be looking for?

 

[- - ex - -]

Thanks for the info. I'm somewhat familiar (I'm studying for a Network+
certification) with ground loops causing problems with regard to computer
LANs using coax; grounding both ends of the coax is the cause of the loop.
How would this circumstance arise in a cable TV setting? There are no
provisions that I'm aware of to ground the TV end of the cable.

It would be grounded at the entry point to the building. If the ground
is incorrect there could be a bigtime difference of potential between
the cable shield and the set.

That is interesting. The TVs in question are in my mother's house, she had
three outlets, but after signal strength problems (on upper channels) the
cable company disconnected one of the three outlets (it was no longer
used). The timing would be about right; that is, the first TV broke a few
months after the third outlet was disconnected. Might something the
serviceman did be the cause? If so, what should I be looking for?

If you're talking months between failures I'd lean towards 'happenstance'.

-Bill M

 

[wolfhedd]

i was just thinkiing about the ground potential as well. also anybody have
a reference voltage that he should suspect so he can test the signal on the
output of his incoming line between the center conductor and the shielded
ground while it is disconnected?
wolf

 

[- - ex - -]

i was just thinkiing about the ground potential as well. also anybody have
a reference voltage that he should suspect so he can test the signal on the
output of his incoming line between the center conductor and the shielded
ground while it is disconnected?
wolf

There shouldn't be any measurable voltage. What is present would be RF
voltage on the order of a few millivolts.
The ground problem would be noticeable as AC voltage between the cable
connector and the connector on the TV. You'd want to measure with a
real low Z meter like a VOM.

-Bill

 

[wolfhedd]

a few millivolts is measurable, and i guess he doesnt have an osci so
wouldnt be too easy. oh well.
wolf

 

[- - ex - -]

a few millivolts is measurable, and i guess he doesnt have an osci so
wouldnt be too easy. oh well.
wolf

I didn't mean to suggest that it was impossible to measure. Sheesh.

-BM

 

[David]

Since you did not give model numbers.
Many older Toshibas were well known for the low vhf band of the tuner to go
out or intermittent when the tv set got old, as well as a known issue in the
aft circuit.
Your RCA is also likely a common known issue with that chassis. 10 years
old could have been one of the infamous ctc177 series chassis that Thomson
was sued over due to the near 100% failure rate.

The cable hook up due to the protection built into modern tuners to prevent
the usual static discharges from causing problems is highly unlikely the
cause of the issues. But standard old age and manufacturing defect related
problems in both the tv sets.

David

 

[Tony Sivori]

Since you did not give model numbers. Many older Toshibas were well
known for the low vhf band of the tuner to go out or intermittent when
the tv set got old, as well as a known issue in the aft circuit. Your
RCA is also likely a common known issue with that chassis. 10 years old
could have been one of the infamous ctc177 series chassis that Thomson
was sued over due to the near 100% failure rate.

The Toshiba is a model CF1927 B. The RCA is a model X20162GS (chassis
CTC146H/L).

The cable hook up due to the protection built into modern tuners to
prevent the usual static discharges from causing problems is highly
unlikely the cause of the issues. But standard old age and
manufacturing defect related problems in both the tv sets.

I agree that it is probably coincidental. But it was rather odd to have
two TVs in the same location to break with very similar symptoms within a
few months of each other. It seems reasonable to question if there was a
single cause, as opposed to coincidence.

 

[Tony Sivori]

a few millivolts is measurable, and i guess he doesnt have an osci so
wouldnt be too easy. oh well.

All I have is a pair of multimeters, one digital and one analog.

 

[Tony Sivori]

It would be grounded at the entry point to the building. If the ground
is incorrect there could be a bigtime difference of potential between
the cable shield and the set.

I will check that.

If you're talking months between failures I'd lean towards
'happenstance'.

I thought it was likely coincidental too. But I was curious as to if a
noncoincidental cause was even possible.

 

[David]

The cf1927 is well known for capacitor failures, including in the AFT
circuit as well as tuner low band vhf failures.

The ctc146L chassis is well known for failure of the video detect coil, aft
coil, as well as tuner failures due to age.

Both failures so far are within the normal failure modes for the tv sets in
question. Not a failure mode that could be caused by something on the cable
line.

David

 

[Glenn Gundlach]

Well, from an RF perspective its impossible. Period. However, from the
standpoint of ground loops resulting from spliced-in unauthorized
connections and/or improper bonding or grounding its very plausible.
The cable people typically won't be much help in this scenario.
As a cable guy for multi years I'd suggest visually tracing the line
right back to the tap and see if anybody has 'messed' with it. If
nothing awry is found I personally would write it off as happenstance.
Any number of scenarios can develop regarding household voltage surges,
weak grounds on the customer's premises and most of such scenarios
reveal themselves by simple visual inspection.
The wiring merits inspection but in my experience I'd vote for
'coincidence' unless there is an obvious wiring fault to the contrary.

-Bill M

Actually, it isn't impossible from an RF perspective. I have an older
Sony with separate RF amps for hi and lo band VHF. The hi band mosfet
failed giving channels 2-6 (not 8!) and 14-69 normal but dead (very
close to it) on channels 7-13 (off air, no cable). I don't know the
innards of Toshiba or RCA, but its a possibility.
GG

 

[- - ex - -]

Actually, it isn't impossible from an RF perspective. I have an older
Sony with separate RF amps for hi and lo band VHF. The hi band mosfet
failed giving channels 2-6 (not 8!) and 14-69 normal but dead (very
close to it) on channels 7-13 (off air, no cable). I don't know the
innards of Toshiba or RCA, but its a possibility.
GG

GG,
How much RF voltage do you have off of your antenna? It would take a
serious amount of RF signal alone to damage your tuner. I had a friend
who worked in broadcasting that claims the front end of the FM radio in
his car was knocked out while working at the transmitter site so I guess
"impossible" might be too strong of a description.
With cable, as the original poster indicated, 10mv of broadband RF would
be the most one could expect to see and that would be abnormal. Even if
the signal were "goosed up" by an internal amp one wouldn't see a volt
of RF before the amp and the tuner went into overload and the pictures
would be seriously degraded.
I don't think a volt of RF would zap a tuner. Maybe, but having that
much available would be difficult to obtain, certainly not via
cable...the signals simply are not that strong.
More likely in your case it was a lighting surge or something like that
and not due to too much RF.

-Bill

 

[Andre]

The cf1927 is well known for capacitor failures, including in the AFT
circuit as well as tuner low band vhf failures.

The ctc146L chassis is well known for failure of the video detect coil, aft
coil, as well as tuner failures due to age.

Both failures so far are within the normal failure modes for the tv sets in
question. Not a failure mode that could be caused by something on the cable
line.

Its usually bad soldering inside the tuner, typically on the centre
pin. I've seen a TV that picked up one channel out of four, when I
resoldered the pin it worked fine.

I've also seen a VCR's converter/modulator with an invisible dry joint
on the pin, cause a similar problem.

 

[Glenn Gundlach]

GG,
How much RF voltage do you have off of your antenna? It would take a
serious amount of RF signal alone to damage your tuner. I had a friend
who worked in broadcasting that claims the front end of the FM radio in
his car was knocked out while working at the transmitter site so I guess
"impossible" might be too strong of a description.
With cable, as the original poster indicated, 10mv of broadband RF would
be the most one could expect to see and that would be abnormal. Even if
the signal were "goosed up" by an internal amp one wouldn't see a volt
of RF before the amp and the tuner went into overload and the pictures
would be seriously degraded.
I don't think a volt of RF would zap a tuner. Maybe, but having that
much available would be difficult to obtain, certainly not via
cable...the signals simply are not that strong.
More likely in your case it was a lighting surge or something like that
and not due to too much RF.

-Bill

I never said or implied the cause of the failure, simply that it
happened. I use a large Winegard antenna in the attic with a Winegard
amp to drive the line. LA metro area direct line of sight to Mt Wilson
about 35 miles. Since the house is still standing 8 years later, it
wasn't lightning. The item was a Sony VTX-1000, the tuner part of the
'Profeel' line. It was about 10 years old when it failed. I bought the
exact mosfet from Sony and replaced it. Worked fine.

Resume: FCC first phone license before it became a fishing license
with a broadcast endorsement. Worked at a CBS affiliate for 8 years
and did sweep alignments on the Harris BT18-L2 transmitter. I figure
this qualifies me to repair the individual components in the tuner.

GG

 

[- - ex - -]

I never said or implied the cause of the failure, simply that it
happened. I use a large Winegard antenna in the attic with a Winegard
amp to drive the line. LA metro area direct line of sight to Mt Wilson
about 35 miles. Since the house is still standing 8 years later, it
wasn't lightning. The item was a Sony VTX-1000, the tuner part of the
'Profeel' line. It was about 10 years old when it failed. I bought the
exact mosfet from Sony and replaced it. Worked fine.

Resume: FCC first phone license before it became a fishing license
with a broadcast endorsement. Worked at a CBS affiliate for 8 years
and did sweep alignments on the Harris BT18-L2 transmitter. I figure
this qualifies me to repair the individual components in the tuner.

GG

No, you replied with the implication that RF matters could have blown
out the guy's tuner and that I was incorrect in saying otherwise. I
respect all your "fishing licenses" and repair skills but in context
with the whole thread I can bet your attic antenna 35 miles away from
Mt. Wilson had zip to do with your particular failure or else there
would be 10 million similar reports from the LA metro area. The fact
that your house hasn't burnt down in eight years isn't a very cogent
argument for why it must be an RF issue as opposed to lightning or line
surges.
The 'difference of potential' ground scenario is very real and very
common and will kill a MOSFET in a heartbeat. But, again in context,
two ten year old TVs, and your 10 year old VCR, dying within a matter
of months on the same premises would hardly suggest that too much RF
from the cable was the problem.

-BM