TV antenna... explodes!

[Menticol]

Hi again guys!

I'm having serious problems with a very, very old SONY KV82ME7. I know it's a ... again, very old! TV, but it belongs to a low-income family, so I must fix it to sleep well.

The antenna female jack wasn't the one I was used to

example:
**broken link removed**

Instead, a strange jack

**broken link removed**

I removed the strange jack and soldered a common female jack. But, when I plug the coaxial coming from the antenna... explodes!!

I'm sure the female jack is energized, but I don't know why! The explosion only occurs when the coaxial makes full contact with the TV... if only the central pin is connected, the TV works great (I saw the Obama's speech on it)

I didn't changed anything else, and the wiring is OK (the antenna is not touching the PSU or anything else)

What's going on?

 

[Menticol]

Just in case that any person in the world has the same problem:

I've found the deal. In older TV's, the chassis is energized! It was a new, really amazing discovery form me, after too much explosions and zaps.

I've added a Balun between my new jack and the TV's sintonizer PCB... and problem gone! Somebody told me a ceramic capacitor would to the trick too.

The "modified" balun was made with a 75-to-300 ohm common balun, take a look

 

[Torben]

Hi Menticol!

Thanks for posting what you found out. Too many people post questions and never post when they figure out the answer.

If there is another way to deal with the problem, hopefully somebody more knowledgeable than I will post it.


Regards,

Torben

P.S. - I am not trying to criticize; just trying to help and I hope you would do the same for me if I were speaking Spanish . But: "to electrocute" means "to kill by electric shock". So if no-one died, there was no electrocution. So hopefully there were no electrocutions but just painful zaps (and exploded antennas).

 

[Menticol]

So if no-one died, there was no electrocution. So hopefully there were no electrocutions but just painful zaps (and exploded antennas).

Thank you so much by your correction Torben! I learn a lot of new vocabulary (for daily-use and technical) here. Another good motivation is, even for a non-native speaker, reading "Pls Sir. I need do of homework circuit measure water tnx" is very uncomfortable

PS: A good advice I always follow

If you have a problem...
If google translate can't help...
And if you can find it...
Maybe you can use...
MS PAINT!

I'm gonna use it as signature!

 

[Nigel Goodwin]

If you know so little about TV's you really shouldn't be trying to repair them for people - this is how TV's always used to be, live chassis's were the norm for decades.

The aerial socket would normally be isolated by special isolating capacitors, usually (in more modern sets) built-in as part of the socket itself.

BTW, it's not a 'strange jack' - it looks like a Belling Lee Coaxial Socket - the standard aerial connection for most of the planet.

 

[Menticol]

If you know so little about TV's you really shouldn't be trying to repair them for people - this is how TV's always used to be, live chassis's were the norm for decades.

Yes That's why I only work for friends and for free. Normally, after discharging the CRT, I look for obvious signs of failure (blown capacitors, brown board). If that fails, googling the failure, usually I get where is located (i.e. check and replace V sync caps, your diode is blown, etc.). More complex failures are beyond my spectrum.

The aerial socket would normally be isolated by special isolating capacitors, usually (in more modern sets) built-in as part of the socket itself.

You are right, I'm pretty sure the little box I discarded contained them. I'll never do again such a thing

BTW, it's not a 'strange jack' - it looks like a Belling Lee Coaxial Socket - the standard aerial connection for most of the planet.

You are right again! Thanks for the name. I had never seen a Belling Lee on a old or new TV before. I remember them in CB radios, but on old TV sets, a pair of screws for the UHF antenna was the rule for me.

Offtopic: I've dismantled every household equipment, except microwave ovens and plasmas (for safety and price, respectively). A photocopier is, for now, the most complex and beautiful mechanism a home can get! thousands of gears and screws...

 

[Rolf]

Hi again guys!

I'm having serious problems with a very, very old SONY KV82ME7. I know it's a ... again, very old! TV, but it belongs to a low-income family, so I must fix it to sleep well.

The antenna female jack wasn't the one I was used to

example:
**broken link removed**

Instead, a strange jack

**broken link removed**

I removed the strange jack and soldered a common female jack. But, when I plug the coaxial coming from the antenna... explodes!!

I'm sure the female jack is energized, but I don't know why! The explosion only occurs when the coaxial makes full contact with the TV... if only the central pin is connected, the TV works great (I saw the Obama's speech on it)

I didn't changed anything else, and the wiring is OK (the antenna is not touching the PSU or anything else)

What's going on?

Sounds like the chassis is hot, has 120v AC on it. Did they make TV's without transformers, like some radios. Then if the power plug got reversed of if the wall socket was reversed it would cause the problem you describe.
Get your voltmeter out and make a check.

 

[Nigel Goodwin]

Sounds like the chassis is hot, has 120v AC on it. Did they make TV's without transformers, like some radios. Then if the power plug got reversed of if the wall socket was reversed it would cause the problem you describe.

ALL TV's used to be like that, originally they used half wave rectifiers (usually metal ones), so the chassis was full live mains if the plug was reversed. Later, because the electricity companies complained about the mains been pulled to a DC offset, they started using bridge rectifiers - which left the chassis live at half mains potential regardless of the plug direction.

The only socket on the sets was the aerial socket, and these were isolated by special capacitors on both connections.

Later, with the advent of switchmode supplies and AV inputs, the main part of the chassis was isolated, and the aerial socket became directly connected to the chassis. There were also a very tiny number of sets that used conventional mains transformers for isolation, but these were very uncommon.

My boss broke his arm because someone had bodged an old TV by shorting out the faulty aerial coupling capacitors - he was doing an aerial, which was on a pole stuck in the ground - he pulled the pole out of the ground and got full 240V straight across him, throwing him across the garden, breaking his arm.

 

[ericgibbs]

ALL TV's used to be like that, originally they used half wave rectifiers (usually metal ones), so the chassis was full live mains if the plug was reversed. Later, because the electricity companies complained about the mains been pulled to a DC offset, they started using bridge rectifiers - which left the chassis live at half mains potential regardless of the plug direction.

The only socket on the sets was the aerial socket, and these were isolated by special capacitors on both connections.

hi,
A fatal mistake sometimes times made was to stand in the loft adjusting the indoor aerial with one hand, while using the other hand on the lofts water tank to steady themselves.
IF the aerial connector isolation caps had been shorted for any reason and the TV mains plug connections reversed,
ie: a live chassis, it usually killed the DIY'r.

My advice would be, when working on a very old TV is to ensure that the mains to plug is correctly wired and the metal chassis of the TV is on the NEUTRAL wire.

 

[Nigel Goodwin]

My advice would be, when working on a very old TV is to ensure that the mains to plug is correctly wired and the metal chassis of the TV is on the NEUTRAL wire.

Are there any half wave rectifier TV's still in use in the UK?, most would have been 405 lines

 

[ericgibbs]

Are there any half wave rectifier TV's still in use in the UK?, most would have been 405 lines

hi,
I do remember some 625 line sets with half phase!.

Worked for Rediffusion 1957-60 and Belcher Radio [mainly Currys equipment] from 1961-64 as a Service engineer, thats how I know your home area.

Creswell had 30Hz and DC mains.... happy days!

 

[Nigel Goodwin]

hi,
I do remember some 625 line sets with half phase!.

Even some early colour sets were - but the majority of halfwave sets were 405 or dual-standard.

I'm just trying to remember if the Thorn 3000 had a bridge?, I really can't remember, I'll have to see if I can find the manual.

Worked for Rediffusion 1957-60 and Belcher Radio [mainly Currys equipment] from 1961-64 as a Service engineer, thats how I know your home area.

Creswell had 30Hz and DC mains.... happy days!

I was fortunate to be later, so no 'funny' mains - although I believe some parts of Stavely are still fed from Stavely Works with peculiar mains (can't remember what though?).

 

[ericgibbs]

E

I was fortunate to be later, so no 'funny' mains - although I believe some parts of Stavely are still fed from Stavely Works with peculiar mains (can't remember what though?).

hi,
Staveley, was [is?] 30Hz, we had to fit very large extra caps on the HT power rails, severe problems otherwise with frame lock/roll.

In Creswell had to use a gas soldering iron as the supply from the 'pit' was dc.

 

[Menticol]

Mains here used to be (circa 1950) 150VAC. Now is 115-120VAC, 60Hz. Interesting explosions of 115VAC equipment connected in very old houses.

I've heard that early household wires were made of silver, instead of copper is that feasible?

hi,
Worked for Rediffusion 1957-60 and Belcher Radio [mainly Currys equipment] from 1961-64 as a Service engineer, thats how I know your home area.

Creswell had 30Hz and DC mains.... happy days!

As a service engineer, I guess you may remember ugly places to work

I bet all of you had to work sometime on a creepy old house! The dust and specially spiders, bees and that kind of bugs, most of them unknown for the science ... creeepy!

Past year I had to re-wire the switches, lamps and outlets inside an old house. When you stopped to take a short nap after lunch, started to hear kids playing around on the stairs (what kids? I was alone!)

And another ugly location, I have a special fear to pool machine rooms, and everything related with submerged pumps and big water tanks.

 

[Hero999]

I've had a shock from relatively modern TV coaxial sockets.

It's pretty common for CRTs and is nothing to worry about. The CRT generatates static electricity when in use making all of the connections inside at a high potential relative to earth. Most modern TVs are double insulated to the capactances between the earthed mains and TV become charged up to a high voltage. Fortunately the capacitances are very small so you won't receive any more than a low power static shock.

 

[er_rajeshkumar2002]

The only socket on the sets was the aerial socket, and these were isolated by special capacitors on both connections.

Later, with the advent of switchmode supplies and AV inputs, the main part of the chassis was isolated, and the aerial socket became directly connected to the chassis. There were also a very tiny number of sets that used conventional mains transformers for isolation, but these were very uncommon.

 

[ericgibbs]

As a service engineer, I guess you may remember ugly places to work

hi,
On my 'dont' like list, as a service engineer, are dogs, christmas trees on top of the TV, kids crawling all over my tool kit while Im trying to work, carrying 26inch console TV's up/down stairs in tower blocks when the lifts dont work...etc.

My worst experience is when I accidentally trod in some dog sh*t and walked it all over a customers white wollen carpet.. to make it worse the customer was an Italian woman and didnt speak any English... I learned a few Italian expletives that day.!

 

[Nigel Goodwin]

I've had a shock from relatively modern TV coaxial sockets.

It's pretty common for CRTs and is nothing to worry about. The CRT generatates static electricity when in use making all of the connections inside at a high potential relative to earth. Most modern TVs are double insulated to the capactances between the earthed mains and TV become charged up to a high voltage. Fortunately the capacitances are very small so you won't receive any more than a low power static shock.

Partially true - but not correct.

Essential safety components in a TV (or VCR etc.) connect between chassis and the mains (usually from the negative connection of the bridge rectifier). The components are a high value resistor and a capacitor in parallel - there purpose is to discharge any voltage buildup back to ground via the mains.

The resistor and capacitor do (obviously) pass a small current from the mains to the chassis, leaving it floating at half mains potential (120V in the UK) via a high resistance. It's this tiny leakage current at 120V that you can feel.

 

[Nigel Goodwin]

My worst experience is when I accidentally trod in some dog sh*t and walked it all over a customers white wollen carpet.. to make it worse the customer was an Italian woman and didnt speak any English... I learned a few Italian expletives that day.!

My worst was when I was sent to change over a rental TV, the customer hadn't been paying his rental, and he claimed it's because the TV was no good.

The customer had three large dogs, none of which were allowed outside, and the carpet was soaked in dog p*ss and there were large piles of dog sh*t all over the floor - plus two small children were crawling on the floor through it eating biscuits.

To make matters worse, I had to change the plug on the TV - an act I managed without breathing in once

I drove back to the shop with my head out of the van window, and just threw the old set in the yard when I got back.

Needless to say they still didn't pay for the new set (which I had always said they wouldn't), and my boss told me to go and collect the set - upon which I told him where he could stuff his set!

Don't know if anyone else ever collected it, but I didn't.

 

[Alyssa28]

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