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Title: Why are most TVs ungrounded these days
Post by: Lyle Williams on May 12, 2017, 04:31:23 AM

Why are most TVs ungrounded these days?

Figure 8 power leads seem to be very common, so sets find ground via signal cables.

Title: Re: Why are most TVs ungrounded these days
Post by: Steve M Smith on May 12, 2017, 04:37:57 AM

I can't recall ever seeing a TV with a ground connection (UK).


Steve.

Title: Re: Why are most TVs ungrounded these days
Post by: Tim Weaver on May 12, 2017, 11:29:37 AM

Since they are made of plastic, the path to ground is highly unlikely to go through a human on its way out.

Cable boxes don't sue for wrongful death. So who cares if the safety ground goes out through signal cables. We can save $0.08 per unit.

Title: Re: Why are most TVs ungrounded these days
Post by: John Roberts {JR} on May 12, 2017, 11:51:08 AM

As long as the mains wiring is double insulated there is little need for grounded chassis. Since TV frame rate is at or near mains frequency, mains frequency noise injected into grounds could cause visible interference.

I can't recall ever seeing a grounded line cord on TV receiver, but I do remember hot chassis TV sets from back in the day.

JR

Title: Re: Why are most TVs ungrounded these days
Post by: Lyle Williams on May 14, 2017, 02:23:26 AM

Hum wise, it seems like a questionable design decision.

Title: Re: Why are most TVs ungrounded these days
Post by: John Rutirasiri on May 14, 2017, 11:28:43 AM

Quote from: Lyle Williams on May 14, 2017, 02:23:26 AM

Hum wise, it seems like a questionable design decision.

In the "old days" (as if 5 years was eons ago), plasma TV sets would employ ground on the power cord because of the flyback transformers and high voltage needed to drive the plasma screen, and back panel of the TVs being made of metal to support the weight of the screen.  (I've had more than a fair share of ground loop issue with Panasonic plasmas hooked up to sound systems.)

In the early days of LCD TVs, the backlighting was CCFL tubes, which also employed flybacks.

These days it's all LCD TV's using LED backlighting (so-called "LED TVs").  The outer case is all plastic with maybe metal inner frame for structure and wall mount.  Current draw is 1A - 2A versus 5A-7A for plasma.

John R.

Title: Re: Why are most TVs ungrounded these days
Post by: Dennis Wiggins on May 30, 2017, 06:15:26 PM

Quote from: John Roberts {JR} on May 12, 2017, 11:51:08 AM

As long as the mains wiring is double insulated there is little need for grounded chassis. Since TV frame rate is at or near mains frequency, mains frequency noise injected into grounds could cause visible interference.

I can't recall ever seeing a grounded line cord on TV receiver, but I do remember hot chassis TV sets from back in the day.

JR

Ahh... the origin of the "cheater cord".

http://amradio.mailman.qth.narkive.com/mrdokYAm/what-is-the-origin-of-the-name-cheater-cord

I, too, was a curious teenager..   :P

-Dennis